SCION Control-Plane PKI
draft-dekater-scion-pki-00
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| Authors | Corine de Kater , Nicola Rustignoli | ||
| Last updated | 2022-08-26 | ||
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draft-dekater-scion-pki-00
Network Working Group C. de Kater
Internet-Draft N. Rustignoli
Intended status: Informational ETH Zuerich
Expires: 27 February 2023 26 August 2022
SCION Control-Plane PKI
draft-dekater-scion-pki-00
Abstract
This document presents the trust concept and design of the SCION
_control-plane PKI_, SCION's public key infrastructure model. SCION
(Scalability, Control, and Isolation On Next-generation networks) is
a path-aware, inter-domain network architecture. The control-plane
PKI, or short CP-PKI, handles cryptographic material and lays the
foundation for the authentication procedures in SCION. It is used by
SCION's control plane to authenticate and verify path information,
and builds the basis for SCION's special trust model based on so-
called Isolation Domains.
The document first describes the trust model behind SCION's control-
plane PKI, and provides a short overview of the certificates, keys,
and roles involved. It then continues with detailed specifications
of the building blocks of SCION's control-plane PKI. The document
concludes with several considerations in regard to deploying the
control-plane PKI.
About This Document
This note is to be removed before publishing as an RFC.
The latest revision of this draft can be found at
https://scionassociation.github.io/scion-cppki_I-D/draft-dekater-
scion-pki.html. Status information for this document may be found at
https://datatracker.ietf.org/doc/draft-dekater-scion-pki/.
Source for this draft and an issue tracker can be found at
https://github.com/scionassociation/scion-cppki_I-D.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Conventions and Definitions . . . . . . . . . . . . . . . 3
1.2. Trust Model . . . . . . . . . . . . . . . . . . . . . . . 4
1.3. Trust Relations within an Isolation Domain . . . . . . . 5
1.3.1. Updates and Trust Resets . . . . . . . . . . . . . . 6
1.4. Overview of Certificates, Keys, and Roles . . . . . . . . 6
1.5. Trust Concept as a Function . . . . . . . . . . . . . . . 8
1.5.1. Input . . . . . . . . . . . . . . . . . . . . . . . . 8
1.5.2. Output . . . . . . . . . . . . . . . . . . . . . . . 9
2. Certificate Specification . . . . . . . . . . . . . . . . . . 9
2.1. SCION Control-Plane PKI Keys and Certificates -
Overview . . . . . . . . . . . . . . . . . . . . . . . . 9
2.2. Certificate Specification . . . . . . . . . . . . . . . . 13
2.2.1. General Certificate Requirements . . . . . . . . . . 13
2.2.2. Control-Plane Root Certificate . . . . . . . . . . . 24
2.2.3. Control-Plane CA Certificate . . . . . . . . . . . . 26
2.2.4. Control-Plane AS Certificate . . . . . . . . . . . . 27
2.2.5. Voting Certificates . . . . . . . . . . . . . . . . . 28
3. Specification of the Trust Root Configuration . . . . . . . . 30
3.1. TRC Specification . . . . . . . . . . . . . . . . . . . . 30
3.1.1. TRC Types and States . . . . . . . . . . . . . . . . 30
3.1.2. TRC Format . . . . . . . . . . . . . . . . . . . . . 33
3.1.3. TRC Signature Syntax . . . . . . . . . . . . . . . . 41
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3.1.4. Control-Plane Certification Path . . . . . . . . . . 44
3.1.5. TRC Updates . . . . . . . . . . . . . . . . . . . . 46
3.2. TRC Signing Ceremony . . . . . . . . . . . . . . . . . . 50
3.2.1. Non-Base TRC Updates . . . . . . . . . . . . . . . . 51
3.2.2. TRC Signing Ceremony - Base TRC . . . . . . . . . . 51
4. Deploying the CP PKI - Specifications . . . . . . . . . . . . 58
4.1. Deploying a TRC . . . . . . . . . . . . . . . . . . . . . 58
4.1.1. Base TRC . . . . . . . . . . . . . . . . . . . . . . 58
4.1.2. TRC Update . . . . . . . . . . . . . . . . . . . . . 58
4.2. Signing and Verifying Control-Plane Messages . . . . . . 59
4.2.1. Signing a Control-Plane Message . . . . . . . . . . 59
4.2.2. Verifying a Control-Plane Message . . . . . . . . . 60
4.3. Creating a New Control-Plane AS Certificate . . . . . . . 62
5. Security Considerations . . . . . . . . . . . . . . . . . . . 62
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 62
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 62
7.1. Normative References . . . . . . . . . . . . . . . . . . 62
7.2. Informative References . . . . . . . . . . . . . . . . . 62
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 64
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 64
1. Introduction
The control-plane PKI (CP-PKI) lays the foundation for the
authentication procedures in SCION. It handles all cryptographic
material used in the public key infrastructure of SCION's control
plane. This section first introduces the key concepts of the SCION
CP-PKI, including the trust model, its core elements (certificates,
keys, and roles), and their relationships. The sections after the
Introduction provide detailed specifications of the building blocks
of the CP-PKI.
*Note:* For more detailed information on the SCION next-generation
inter-domain architecture, see [CHUAT22], especially Chapter 2, as
well as the IETF Internet Drafts [I-D.scion-overview] and
[I-D.scion-components].
1.1. Conventions and Definitions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
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1.2. Trust Model
Given the diverse nature of the constituents in the current Internet,
an important challenge is how to scale authentication of network
elements (such as AS ownership, hop-by-hop routing information, name
servers for DNS, and domains for TLS) to the global environment. The
roots of trust of currently prevalent public key infrastructure (PKI)
models do not scale well to a global environment, because (1)
mutually distrustful parties cannot agree on a single trust root
(monopoly model), and because (2) the security of a plethora of roots
of trust is only as strong as its weakest link (oligopoly model) -
see also [BARRERA17].
The monopoly model suffers from two main drawbacks: First, all
parties must agree on a single root of trust. Secondly, the single
root of trust represents a single point of failure, the misuse of
which enables the forging of certificates. Also, its revocation can
result in a kill-switch for all the entities it certifies. The
oligopoly model relies on several roots of trust, all equally and
completely trusted. However, this is not automatically better:
Whereas the monopoly model has a single point of failure, the
oligopoly model has the drawback of exposing more than one point of
failure.
Thus, there is a need for a trust architecture that supports
meaningful trust roots in a global environment with inherently
distrustful parties. This new trust architecture should provide the
following properties:
* Trust agility (see further below);
* Resilience to single root of trust compromise;
* Multilateral governance; and
* Support for policy versioning and updates.
Ideally, the trust architecture allows parties that mutually trust
each other to form their own trust "union" or "domain", and to freely
decide whether to trust other trust unions (domains) outside their
own trust bubble.
To fulfill the above requirements, which in fact apply well to inter-
domain networking, SCION introduces the concept of *Isolation
Domains*. An Isolation Domain (ISD) is a building block for achieving
high availability, scalability, and support for heterogeneous trust.
It consists of a logical grouping of ASes that share a uniform trust
environment (i.e., a common jurisdiction). An ISD is administered by
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multiple ASes that form the ISD core; these are the *core ASes*. It
is governed by a policy called the *Trust Root Configuration* (TRC),
which is negotiated by the ISD core. The TRC defines the locally
scoped roots of trust used to validate bindings between names and
public keys.
Authentication in SCION is based on digital certificates that bind
identifiers to public keys and carry digital signatures that are
verified by roots of trust. SCION allows each ISD to define its own
set of trust roots, along with the policy governing their use. Such
scoping of trust roots within an ISD improves security, as compromise
of a private key associated with a trust root cannot be used to forge
a certificate outside the ISD. An ISD's trust roots and policy are
encoded in the TRC, which has a version number, a list of public keys
that serves as root of trust for various purposes, and policies
governing the number of signatures required for performing different
types of actions. The TRC serves as a way to bootstrap all
authentication within SCION. Additionally, TRC versioning is used to
efficiently revoke compromised roots of trust.
The TRC also provides _trust agility_, that is, it enables users to
select the trust roots used to initiate certificate validation. This
implies that users are free to choose an ISD they believe maintains a
non-compromised set of trust roots. ISD members can also decide
whether to trust other ISDs and thus transparently define trust
relationships between parts of the network. SCION trust model,
therefore, differs from the one provided by other PKI architectures.
1.3. Trust Relations within an Isolation Domain
As already mentioned previously, the control-plane PKI, SCION's
concept of trust, is organized on ISD-level. Each ISD can
independently specify its own Trust Root Configuration (TRC) and
build its own verification chain. Each TRC consists of a collection
of signed root certificates, which are used to sign CA certificates,
which are in turn used to sign AS certificates. The TRC also
includes ISD-policies that specify, for example, the TRC's usage,
validity, and future updates. A TRC is a fundamental component of an
ISD's control-plane PKI. The so-called *base TRC* constitutes the
ISD's trust anchor. It is signed during a signing ceremony and then
distributed throughout the ISD.
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1.3.1. Updates and Trust Resets
There are two types of TRC updates: regular and sensitive. A
*regular TRC update* is a periodic re-issuance of the TRC where the
entities and policies listed in the TRC remain unchanged, whereas a
*sensitive TRC update* is an update that modifies critical aspects of
the TRC, such as the set of core ASes. In both cases, the base TRC
remains unchanged. If the ISD's TRC has been compromised, it is
necessary for an ISD to re-establish the trust root. This is
possible with a process called *trust reset* (if allowed by the ISD's
trust policy). In this case, a new base TRC is created.
1.4. Overview of Certificates, Keys, and Roles
The base TRC constitutes the root of trust within an ISD. Figure 1
provides a first impression of the trust chain within an ISD, based
on its TRC. For detailed descriptions, please refer to Section 2 and
Section 3.
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TRC 2
+--------------------------------------+
|+------------------------------------+|
||- Version - Core ASes ||
+--------+ ||- ID - Description || +--------+
| TRC 1 | ||- Validity - No Trust Reset || | TRC 3 |
| (Base |---->||- Grace Period - Voting Quorum ||--->| |
| TRC) | ||- ... || | |
+--------+ |+------------------------------------+| +--------+
|+----------------+ +----------------+|
|| Regular Voting | |Sensitive Voting||
|| Certificate | | Certificate ||
|+----------------+ +----------------+|
|+----------------+ +----------------+|
|| Votes | | Signatures ||
|+----------------+ +----------------+|
|+------------------------------------+|
|| CP Root Certificates ||
|+----------+-------------+-----------+|
| | | |
+-----------+-------------+------------+
| |
| |
v v
+-----------+ +-----------+
| CP CA | | CP CA |
|Certificate| |Certificate|
+-+-------+-+ +-----+-----+
| | |
| | |
v v v
+-----------+ +-----------+ +-----------+
| CP AS | | CP AS | | CP AS |
|Certificate| |Certificate| |Certificate|
+-----------+ +-----------+ +-----------+
Figure 1: Chain of trust within an ISD
All certificates used in SCION's control-plane PKI are in X.509 v3
format [RFC5280]. Additionally, the TRC contains self-signed
certificates instead of plain public keys. Self-signed certificates
have the following advantages over plain public keys: (1) They make
the binding between name and public key explicit; and (2) the binding
is signed to prove possession of the corresponding private key.
All ASes in SCION have the task to sign and verify control-plane
messages. However, certain ASes have additional roles:
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* *Core ASes*: Core ASes are a distinct set of ASes in the SCION
control plane. For each ISD, the core ASes are listed in the TRC.
Each core AS in an ISD has links to other core ASes (in the same
or in different ISDs).
* *Certification authorities (CAs)*: CAs are responsible for issuing
AS certificates to other ASes and/or themselves.
* *Voting ASes*: Only certain ASes within an ISD may sign TRC
updates. The process of appending a signature to a new TRC is
called "casting a vote"; the designated ASes that hold the private
keys to sign a TRC update are "voting ASes".
All further details of the SCION control-plane PKI are specified in
the following sections.
1.5. Trust Concept as a Function
The SCION control-plane PKI can be seen as a function that transforms
potential distrust among different parties into a mutually accepted
trust contract including a trust update and reset policy as well as
certificates used for authentication procedures in SCION's control
plane.
For the function to work, it is not necessary that the ASes of the
ISD all trust each other. However, all ASes MUST trust the ISD's
core ASes, authoritative ASes, voting ASes, as well as its CA(s).
These trusted parties negotiate the ISD trust contract in a
"bootstrapping of trust" ceremony, where cryptographic material is
exchanged, and the ISD's trust anchor, the initial Trust Root
Configuration, is created and signed.
1.5.1. Input
Prior to the ceremony, the trusted parties must decide about the
validity period of the TRC as well as the number of votes required to
update a TRC. They must also bring the required keys and
certificates, the so-called root and voting keys/certificates.
During the ceremony, the trusted parties decide about the number of
the ISD, which must be an integer in the inclusive range between 1
and 65535.
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1.5.2. Output
The output of the bootstrapping of trust ceremony, or the trust
"function", are the ISD's initial Trust Root Configuration as well as
mutually trusted and accepted CA and AS certificates--the latter are
used to verify SCION's control-plane messages. Together with the
ISD's control-plane root certificates, the CA and AS certificates
build the ISD's trust and verification chain.
2. Certificate Specification
This section provides a detailed specification of all certificates
used in SCION's control-plane PKI. It starts with an overview of the
main keys and certificates.
2.1. SCION Control-Plane PKI Keys and Certificates - Overview
All certificates in SCION's control-plane PKI are in X.509 v3 format
[RFC5280]. Each certificate has a subject (the entity that owns the
certificate) and an issuer (the entity that signed the certificate,
usually a CA). In the case of self-signed certificates, the subject
and the issuer are the same entity.
There are three types of control-plane (CP) certificates: root
certificates, CA certificates, and AS certificates. Together, they
build a chain of trust that is anchored in the trust root
configuration (TRC) file of the respective Isolation Domain (ISD).
Additionally, there are regular and sensitive voting certificates,
which define the keys to cast votes in a regular and a sensitive TRC
update, respectively.
The following list summarizes the main certificates and corresponding
key pairs of SCION's control-plane PKI as well as the voting
certificates and keys:
* *Control-Plane Root Certificates* - Control-plane (CP) root
certificates are used to verify control-plane CA certificates.
Control-plane root certificates are embedded in TRCs, to
facilitate the bootstrapping of trust.
- _CP root private key_: This private key is used to sign
control-plane CA certificates.
- _CP root certificate_: This is the container for the public key
associated with the CP root private key.
- Section 2.2.2 provides more details on the CP root
certificates.
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* *Control-Plane CA Certificates* - Control-plane (CP) CA
certificates are used to verify AS certificates.
- _CP CA private key_: This private key is used by the CA to sign
AS certificates.
- _CP CA certificate_: This is the container for the public key
associated with the CP CA private key.
- Section 2.2.3 provides more details on the CP CA certificates.
* *Control-Plane AS Certificates* - Control-plane (CP) AS
certificates are used to verify control-plane messages such as
path-segment construction beacons (PCB). PCBs explore network
paths within an ISD.
- _CP AS private key_: This private key is used by an AS to sign
control-plane messages.
- _CP AS certificate_: This is the container for the public key
associated with the CP AS private key.
- Section 2.2.4 provides more details on the CP AS certificates.
*Note:* The TRC of each ISD contains a trusted set of control-plane
root certificates. This set builds the root of each ISD's
verification path. For more information on the selection of this
trusted set of root certificates, see Section 3.
* *Voting Certificates* - Regular and sensitive voting certificates
are used to verify regular and sensitive TRC updates,
respectively.
- _Regular voting private key_: This private key is used to sign
regular TRC updates. The corresponding public key is embedded
in TRCs (via the regular voting certificate).
- _Regular voting certificate_: This is the container for the
public key associated with the regular voting private key.
- _Sensitive voting private key_: This private key is used to
sign sensitive TRC updates. The corresponding public key is
embedded in TRCs (via the sensitive voting certificate).
- _Sensitive voting certificate_: This is the container for the
public key associated with the sensitive voting private key.
- Section 2.2.5 provides more details on the voting certificates.
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Table 1 and Table 2 below provide a formal overview of the different
types of key pairs and certificates in the control-plane PKI.
+======================+==============+=========================+
| Name | Notation (1) | Used to verify/sign |
+======================+==============+=========================+
| Sensitive voting key | K_sens | TRC updates (sensitive) |
+----------------------+--------------+-------------------------+
| Regular voting key | K_reg | TRC updates (regular) |
+----------------------+--------------+-------------------------+
| CP root key | K_root | CP CA certificates |
+----------------------+--------------+-------------------------+
| CP CA key | K_CA | CP AS certificates |
+----------------------+--------------+-------------------------+
| CP AS key | K_AS | PCBs, path segments |
+----------------------+--------------+-------------------------+
Table 1: Key chain
(1) K_x = PK_x + SK_x, where x = certificate type, PK_x = public key,
and SK_x = private key
+==============+==========+============+=================+==========+
| Name | Notation | Signed | Contains | Validity |
| | | with | | (2) |
+==============+==========+============+=================+==========+
| TRC (trust | TRC | SK_sens, | C_root, C_sens, | 1 year |
| root conf) | | SK_reg (1) | C_reg (1) | |
+--------------+----------+------------+-----------------+----------+
| Sensitive | C_sens | SK_sens | PK_sens | 5 years |
| voting | | | | |
| cert. | | | | |
+--------------+----------+------------+-----------------+----------+
| Regular | C_reg | SK_reg | PK_reg | 1 year |
| voting | | | | |
| cert. | | | | |
+--------------+----------+------------+-----------------+----------+
| CP root | C_root | SK_root | PK_root | 1 year |
| certificate | | | | |
+--------------+----------+------------+-----------------+----------+
| CP CA | C_CA | SK_root | PK_CA | 11 days |
| certificate | | | | (3) |
+--------------+----------+------------+-----------------+----------+
| CP AS | C_AS | SK_CA | PK_AS | 3 days |
| certificate | | | | |
+--------------+----------+------------+-----------------+----------+
Table 2: Certificates
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(1) Multiple signatures and certificates of each type may be included
in a TRC.
(2) Recommended maximum validity period.
(3) A validity of 11 days with 4 days overlap between two CA
certificates is recommended to enable best possible operational
procedures when performing a CA certificate rollover.
Figure 2 illustrates, at a high level, the relationship between a TRC
and the five types of certificates.
+--------------------+ +--------------------+ +--------------+ +---------------+
| TRC 1 +---->| TRC 2 -+------>╳ | TRC 3 +---->| TRC 4 |
| (base, initial) | | (regular update) | | (base, trust | | (sensitive |
+--+--------------------+ +--------------------+------+ | reset) | | update) |
| | +--------------+ +---------------+
| |
+--------------------------------------------+ +---+----------------------------------------+
| TRC 1 (base, initial) | | TRC 2 (regular update) |
|+------------------------------------------+| |+------------------------------------------+|
||- Version - Core ASes || ||- Version - Core ASes ||
||- ID - Description || ||- ID - Description ||
||- Validity - No Trust Reset || ||- Validity - No Trust Reset ||
||- Grace Period - Voting Quorum || ||- Grace Period - Voting Quorum ||
||- ... || ||- ... ||
|+------------------------------------------+| |+------------------------------------------+|
|+--------------------++--------------------+| |+--------------------++--------------------+|
||Votes (cert.indices)|| Regular Voting || ||Votes (cert.indices)|| Regular Voting ||
|| || Certificates || || || Certificates ||
|| (empty) || || || (1),(2)... || ||
|| ||+-----+ +-----+ || || ||+-----+ +-----+ ||
|| ||| (1) | | (2) | || || ||| (1) | | (2) | ||
|| |||C | |C | ... || || |||C | |C | ... ||
|| ||| reg | | reg | || || ||| reg | | reg | ||
|+--------------------+|+--+--+ +--+--+ || |+--------------------+|+-----+ +-----+ ||
|+--------------------+| | | || |+--------------------+| ||
|| || | +--------++-----+ || || ||
|| || +----------------++-+ | || || ||
|| Signatures |+--------------------+| | | || Signatures |+--------------------+|
|| |+--------------------+| | | || |+--------------------+|
||+------------------+|| Sensitive Voting || | | ||+------------------+|| Sensitive Voting ||
|||73 A9 4E AO 0D ...||| Certificates || | +--+>|48 AE E4 80 DB ...||| Certificates ||
||+------------------+||+-----+ +-----+ || | ||+------------------+||+-----+ +-----+ ||
||+------------------+||| (3) | | (4) | || | ||+------------------+||| (3) | | (4) | ||
|||53 B7 7C 98 56 ...||||C | |C | || +------+>|7E BC 75 98 25 ...||||C | |C | ||
||+------------------+||| sens| | sens| ... || ||+------------------+||| sens| | sens| ... ||
|| ... ||+-----+ +-----+ || || ... ||+-----+ +-----+ ||
|+--------------------++--------------------+| |+--------------------++--------------------+|
|+------------------------------------------+| |+------------------------------------------+|
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|| CP Root Certificates || || CP Root Certificates ||
|| || || ||
|| +-----+ +-----+ +-----+ +-----+ || || +-----+ +-----+ +-----+ +-----+ ||
|| | (5) | | (6) | | (7) | | (8) | || || | (5) | | (6) | | (7) | | (8) | ||
|| |C | |C | |C | |C | || || |C | |C | |C | |C | ||
|| | root| | root| | root| | root| ..... || || | root| | root| | root| | root| ..... ||
|| +-----+ +--+--+ +-----+ +--+--+ || || +-----+ +--+--+ +-----+ +--+--+ ||
|+------------+---------------+-------------+| |+------------+---------------+-------------+|
+-------------+---------------+--------------+ +-------------+---------------+--------------+
| | | |
+---------v-+ +-v---------+ +---------v-+ +-v---------+
| CP CA | | CP CA | | CP CA | | CP CA |
|Certificate| |Certificate| |Certificate| |Certificate|
+-----+-----+ +-----+-----+ +-+-------+-+ +-----+-----+
| | | | |
| | | | |
v v v v v
+-----------+ +-----------+ +-----------+ +-----------+ +-----------+
| CP AS | | CP AS | | CP AS | | CP AS | | CP AS |
|Certificate| |Certificate| |Certificate| |Certificate| |Certificate|
+-----------+ +-----------+ +-----------+ +-----------+ +-----------+
Figure 2: TRC update chain and the different types of associated
certificates. Arrows show how signatures are verified; in other
words, they indicate that a public key contained in a certificate
or TRC can be used to verify the authenticity of another item.
2.2. Certificate Specification
This section provides an in-depth specification of the SCION
certificates. The SCION certificate specification builds on top of
[RFC5280], which in turn builds on top of X.509
(https://handle.itu.int/11.1002/1000/13031). However, the SCION
specification is more restrictive.
This section defines the additional constraints compared to [RFC5280]
for each type of SCION control-plane certificate. The recommended
settings for optional constraints are based on the SCION open source
implementation scionproto (https://github.com/scionproto/scion/).
Adjusting the optional constraints to the requirements of a customer
implementation is possible and allowed.
2.2.1. General Certificate Requirements
SCION control-plane certificates are X.509 v3 certificates. Every
certificate has a subject, which is the entity that owns the
certificate, and an issuer, which is the entity that issued the
certificate, usually a CA.
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The next code block shows the generic format of SCION control-plane
certificates. It is followed by a description of the SCION specifics
for each certificate field.
*Note:* For information regarding the full format, see X.509
(https://handle.itu.int/11.1002/1000/13031), clause 7.2.
TBSCertificate ::= SEQUENCE {
version [0] EXPLICIT Version DEFAULT v1,
serialNumber CertificateSerialNumber,
signature AlgorithmIdentifier{{SupportedAlgorithms}},
issuer Name,
validity Validity,
subject Name,
subjectPublicKeyInfo SubjectPublicKeyInfo,
issuerUniqueID [1] IMPLICIT UniqueIdentifier OPTIONAL, -- disallowed in SCION
subjectUniqueID [2] IMPLICIT UniqueIdentifier OPTIONAL, -- disallowed in SCION
extensions [3] EXPLICIT Extensions OPTIONAL
}
Version ::= INTEGER { v1(0), v2(1), v3(2)} -- v1, v2 are disallowed in SCION
CertificateSerialNumber ::= INTEGER
Validity ::= SEQUENCE {
notBefore Time,
notAfter Time
}
Time ::= CHOICE {
utcTime UTCTime,
generalizedTime GeneralizedTime
}
SubjectPublicKeyInfo ::= SEQUENCE {
algorithm AlgorithmIdentifier{{SupportedAlgorithms}},
subjectPublicKey BIT STRING
}
Extensions ::= SEQUENCE SIZE (1..MAX) OF Extension
Extension ::= SEQUENCE {
extnId OBJECT IDENTIFIER,
critical BOOLEAN DEFAULT FALSE,
extnValue OCTET STRING
-- contains DER encoding of ASN.1 value
-- corresponding to type identified by extnID
}
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2.2.1.1. version Field
The version field MUST be set to v3 in SCION, as extensions are
mandatory.
2.2.1.2. serialNumber Field
The serialNumber field is used as specified in [RFC5280].
2.2.1.3. signature Field
For security reasons, SCION uses a custom list of acceptable
signature algorithms. This list of acceptable signature algorithms
is specified in the signature field.
The list currently only contains the ECDSA signature algorithm
(defined in X.962 (https://standards.globalspec.com/std/1955141/ansi-
x9-62)) - see the code block below. However, the list might be
extended in the future.
The Object Identifiers (OIDs) for ECDSA are defined as ecdsa-with-
SHA256, ecdsa-with-SHA384, and ecdsa-with-SHA512 in [RFC5758]. They
are included as follows:
sigAlg-ecdsa-SHA256 ALGORITHM ::= { OID ecdsa-with-SHA256 }
sigAlg-ecdsa-SHA384 ALGORITHM ::= { OID ecdsa-with-SHA384 }
sigAlg-ecdsa-SHA512 ALGORITHM ::= { OID ecdsa-with-SHA512 }
ecdsa-with-SHA256 OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) ansi-X9-62(10045) signatures(4) ecdsa-with-SHA2(3) 2 }
ecdsa-with-SHA384 OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) ansi-X9-62(10045) signatures(4) ecdsa-with-SHA2(3) 3 }
ecdsa-with-SHA512 OBJECT IDENTIFIER ::= { iso(1) member-body(2)
us(840) ansi-X9-62(10045) signatures(4) ecdsa-with-SHA2(3) 4 }
*Important:* The accepted cryptographic algorithms listed in this
document are the only currently accepted cryptographic algorithms.
SCION implementations MUST reject cryptographic algorithms not found
in the list.
The only accepted curves for ECDSA are:
* NIST P-256 (NISTFIPS186-4 (http://dx.doi.org/10.6028/
NIST.FIPS.186-4), section D.1.2.3) (named secp256r1 in [RFC5480])
* NIST P-384 (NISTFIPS186-4 (http://dx.doi.org/10.6028/
NIST.FIPS.186-4), section D.1.2.4) (named secp384r1 in [RFC5480])
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* NIST P-521 (NISTFIPS186-4 (http://dx.doi.org/10.6028/
NIST.FIPS.186-4), section D.1.2.5) (named secp521r1 in [RFC5480])
The OIDs for the above curves are:
secp256r1 OBJECT IDENTIFIER ::= {
iso(1) member-body(2) us(840) ansi-X9-62(10045) curves(3)
prime(1) 7 }
secp384r1 OBJECT IDENTIFIER ::= {
iso(1) identified-organization(3) certicom(132) curve(0) 34 }
secp521r1 OBJECT IDENTIFIER ::= {
iso(1) identified-organization(3) certicom(132) curve(0) 35 }
The appropriate hash size to use when producing a signature with an
ECDSA key is:
* ECDSA with SHA-256, for a P-256 signing key
* ECDSA with SHA-384, for a P-384 signing key
* ECDSA with SHA-512, for a P-521 signing key
*Important:* SCION implementations MUST include support for P-256,
P-384, and P-521.
2.2.1.3.1. AlgorithmIdentifier Sequence
X.509 (https://handle.itu.int/11.1002/1000/13031) defines the syntax
of the AlgorithmIdentifier as follows:
AlgorithmIdentifier ::= SEQUENCE {
algorithm OBJECT IDENTIFIER,
parameters ANY DEFINED BY algorithm OPTIONAL
}
*Note:* In SCION implementations, the parameters field MUST be
absent, as defined in [RFC8410].
In general, if the AlgorithmIdentifier in a specific SCION
implementation is not defined as described above, the implementation
should stop the validation process entirely and error out.
2.2.1.4. issuer Field
The issuer field contains the distinguished name (DN) of the CA that
created the certificate. The issuer field MUST be non-empty.
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X.501 (http://handle.itu.int/11.1002/1000/13030) (10/2016), clause
9.2, defines the syntax for Name as follows:
Name ::= CHOICE {
rdnSequence RDNSequence
}
RDNSequence ::= SEQUENCE OF RelativeDistinguishedName
RelativeDistinguishedName ::= SET SIZE (1..MAX) OF AttributeTypeAndValue
AttributeType ::= OBJECT IDENTIFIER
AttributeValue ::= ANY -- DEFINED BY AttributeType
In most SCION implementations, the type (AttributeType) will be a
DirectoryString type, outlined as follows:
DirectoryString ::= CHOICE {
teletexStrings TeletexString (SIZE (1..MAX)),
printableString PrintableString (SIZE (1..MAX)),
universalString UniversalString (SIZE (1..MAX)),
utf8String UTF8String (SIZE (1..MAX)),
bmpString BMPString (SIZE (1..MAX)),
}
All SCION implementations MUST support the following standard
attribute types:
* country
* organization
* organizational unit
* distinguished name qualifier
* state or province name
* common name
* serial number
* ISD-AS number
Except for the ISD-AS number attribute, all the above attributes are
defined in [RFC5280].
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As an additional constraint compared to [RFC5280], SCION
implementations MUST use the UTF8String value type for all the above
attributes, including the ISD-AS number attribute.
*Note:* Besides the above listed required attributes, SCION
implementations may additionally also support other attributes.
2.2.1.4.1. ISD-AS number Attribute
The ISD-AS number attribute identifies the SCION ISD and AS. In the
SCION open source implementation, the attribute type is id-at-ia,
defined as:
id-at-ia AttributeType ::= {id-ana id-cppki(1) id-at(2) 1}
where id-ana specifies the root SCION object identifier (OID).
*Note:* The SCION open source implementation currently uses the
Anapaya IANA Private Enterprise Number (55324) as root SCION object
identifier (OID):
id-ana ::= OBJECT IDENTIFIER {1 3 6 1 4 1 55324}
The following points apply when setting the attribute value of the
ISD-AS number attribute:
* The string representation MUST follow the canonical formatting
defined in ISD and AS numbering
(https://github.com/scionproto/scion/wiki/ISD-and-AS-numbering).
* The canonical string representation uses a dash separator between
the ISD and AS numbers.
* The ISD numbers are formatted as decimal.
* The canonical string formatting of AS numbers in the BGP AS range
(0, 2^(32-1)) is the decimal form. Larger AS numbers, i.e., from
2^32 to 2^(48-1), use a 16-bit, colon-separated, lower-case, hex
encoding with leading zeros omitted: 1:0:0 to ffff:ffff:ffff.
*Example:*
AS ff00:0:110 in ISD 1 is formatted as 1-ff00:0:110.
The ISD-AS number attribute MUST be present exactly once in all SCION
control-plane certificates. Implementations MUST NOT create nor
successfully verify certificates that do not include the ISD-AS
number, or include it more than once.
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2.2.1.5. validity Field
Section 4.1.2.5 of [RFC5280] defines the validity field. In addition
to this definition, the following constraints apply to SCION control-
plane certificates:
* All certificates MUST have a well-defined expiration date. SCION
control-plane certificates that use the _99991231235959Z_
generalized time value, instead of a well-defined expiration date,
are not valid. SCION implementations MUST NOT create such
certificates, and verifiers MUST error out when encountering such
a certificate.
* The validity period of a certificate is the period of time in
between the values of the notBefore and notAfter attributes. For
each control-plane certificate type, this validity period must
have a specific maximum value. For more information, see the
following sections describing the control-plane and voting
certificates:
Section 2.2.2, Section 2.2.3, Section 2.2.4, and Section 2.2.5.
2.2.1.6. subject Field
The subject field defines the entity that owns the certificate. It
is specified in the same way as the issuer field (see
Section 2.2.1.4). All SCION control-plane certificates MUST have the
subject field defined (with the same requirements as those for the
issuer field).
2.2.1.7. subjectPublicKeyInfo Field
The subjectPublicKeyInfo field carries the public key of the subject
(the entity that owns the certificate). It identifies which
algorithm to use with the key.
The SCION constraints in Section 2.2.1.3 also apply here: The key
must be a valid key for the selected curve, and the algorithm used
must be included in the list of acceptable signature algorithms. The
list currently only contains the ECDSA signature algorithm (defined
in X.962 (https://standards.globalspec.com/std/1955141/ansi-x9-62)).
2.2.1.8. issuerUniqueID and subjectUniqueID Fields
The fields issuerUniqueID and subjectUniqueID are disallowed and thus
MUST NOT be used in a SCION implementation.
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2.2.1.9. Extensions
X.509 (https://handle.itu.int/11.1002/1000/13031), clause 7.2,
defines the syntax of the Extensions sequence. This section
describes the extensions relevant for SCION.
2.2.1.9.1. authorityKeyIdentifier Extension
The authorityKeyIdentifier extension is defined in clause 9.2.2.1 of
X.509 (https://handle.itu.int/11.1002/1000/13031).
The authorityKeyIdentifier extension identifies the private key used
to sign the certificate. It is defined as follows:
authorityKeyIdentifier EXTENSION ::= {
SYNTAX AuthorityKeyIdentifier
IDENTIFIED BY id-ce-authorityKeyIdentifier
}
AuthorityKeyIdentifier ::= SEQUENCE {
keyIdentifier [0] KeyIdentifier OPTIONAL,
authorityCertIssuer [1] GeneralNames OPTIONAL,
authorityCertSerialNumber [2] CertificateSerialNumber OPTIONAL,
...
}
(WITH COMPONENTS {..., authorityCertIssuer PRESENT,
authorityCertSerialNumber PRESENT } |
WITH COMPONENTS {..., authorityCertIssuer ABSENT,
authorityCertSerialNumber ABSENT } )
KeyIdentifier ::= OCTET STRING
Using the keyIdentifier attribute is the preferred way to specify the
authorityKeyIdentifier extension.
*Important:* SCION implementations may also support the use of the
authorityCertIssuer and authorityCertSerialNumber attributes.
However, if these attributes are set and support for them is missing,
implementations should error out.
This extension MUST always be non-critical (which is the default, see
the code block displaying the generic format of SCION control-plane
certificates in Section 2.2.1). However, SCION implementations MUST
error out if the extension is not present AND the certificate is not
self-signed.
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2.2.1.9.2. subjectKeyIdentifier Extension
The subjectKeyIdentifier extension is defined in clause 9.2.2.2 of
X.509 (https://handle.itu.int/11.1002/1000/13031), (10/2016).
The subjectKeyIdentifier extension identifies the public key being
certified. It can be used, for example, by control-plane messages to
identify which certificate to use for verification. The extension
allows for overlapping control-plane CA keys, for example during
updates. It is defined as follows:
subjectKeyIdentifier EXTENSION ::= {
SYNTAX SubjectKeyIdentifier
IDENTIFIED BY id-ce-subjectKeyIdentifier
}
SubjectKeyIdentifier ::= KeyIdentifier
This extension MUST always be non-critical (which is the default, see
the code block displaying the generic format of SCION control-plane
certificates in Section 2.2.1). However, SCION implementations must
error out if the extension is not present.
2.2.1.9.3. keyUsage Extension
The keyUsage extension is defined in clause 9.2.2.3 of X.509
(https://handle.itu.int/11.1002/1000/13031), (10/2016).
The keyUsage extension identifies the intended usage of the public
key in the corresponding certificate. The ASN.1 definition is as
follows:
keyUsage EXTENSION ::= {
SYNTAX KeyUsage
IDENTIFIED BY id-ce-keyUsage
}
KeyUsage ::= BIT STRING {
digitalSignature (0),
contentCommitment (1),
keyEncipherment (2),
dataEncipherment (3),
keyAgreement (4),
keyCertSign (5),
cRLSign (6),
encipherOnly (7),
decipherOnly (8),
}
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The attributes of the keyUsage extension define the various possible
ways of using the public key. The attributes have the following
meaning in SCION:
* digitalSignature: The public key can be used to verify the digital
signature of a control-plane payload.
* contentCommitment: Not used.
* keyEncipherment: Not used.
* dataEncipherment: Not used.
* keyAgreement: Not used.
* keyCertSign: The public key can be used to verify the CA signature
on a control-plane certificate.
* cRLSign: Not used.
* encipherOnly: Not used.
* decipherOnly: Not used.
*Important:* If the certificate's public key is used to verify the
signature of a control-plane payload (digitalSignature attribute), it
must be possible to trace back the private key used for the
signature. This is done by referencing the ISD-AS and the subject
key identifier (via the subjectKeyIdentifier extension). For more
information about the subjectKeyIdentifier extension, see
Section 2.2.1.9.2.
Each control-plane certificate type uses the public key differently,
and consequently also specifies the attributes of the keyUsage
extension differently. For more information, see the following
sections describing the control-plane and voting certificates:
Section 2.2.2, Section 2.2.3, Section 2.2.4, and Section 2.2.5.
If present, the keyUsage extension should be marked as "critical".
That is, the critical Boolean attribute of this extension must be set
to TRUE (the default is FALSE, see the code block displaying the
generic format of SCION control-plane certificates in Section 2.2.1).
*Note:* If a certificate extension is marked "critical", the public
key in the certificate should only be used for the purpose set in the
critical extension.
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2.2.1.9.4. extKeyUsage Extension
The extKeyUsage extension is defined in clause 9.2.2.4 of X.509
(https://handle.itu.int/11.1002/1000/13031).
The extKeyUsage extension specifies additional usages of the public
key in the certificate. It is defined as follows:
extKeyUsage EXTENSION ::= {
SYNTAX SEQUENCE SIZE (1..MAX) OF KeyPurposeId
IDENTIFIED BY id-ce-extKeyUsage
}
KeyPurposeId ::= OBJECT IDENTIFIER
SCION uses the following attributes of the Extended Key Usage
extension, as defined in Section 4.2.1.12 of [RFC5280]:
* id-kp-serverAuth: If set, the public key can be used for SCION
control-plane server authentication.
* id-kp-clientAuth: If set, the public key can be used for SCION
control-plane client authentication.
* id-kp-timeStamping: If set, the public key can be used for the
verification of timestamps.
This extension MUST be present in control-plane root-, AS- and voting
certificates. It MAY be present in control-plane CA certificates.
For the exact settings per certificate type, see the below sections
describing the control-plane and voting certificates: Section 2.2.2,
Section 2.2.3, Section 2.2.4, and Section 2.2.5.
2.2.1.9.5. basicConstraints Extension
The basicConstraints extension is defined in clause 9.4.2.1 of X.509
(https://handle.itu.int/11.1002/1000/13031).
The basicConstraints extension specifies whether the certificate
subject may act as a CA. The ASN.1 definition for the
basicConstraints extension is as follows:
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basicConstraints EXTENSION ::= {
SYNTAX BasicConstraintsSyntax
IDENTIFIED BY id-ce-basicConstraints
}
BasicConstraintsSyntax ::= SEQUENCE {
cA BOOLEAN DEFAULT FALSE,
pathLenConstraint INTEGER(0..MAX) OPTIONAL,
}
* cA attribute: Specifies whether the certificate subject may act as
a CA. If yes, this attribute MUST be set to TRUE.
* pathLenConstraint attribute: This attribute is only relevant if
the cA attribute is set to TRUE. It specifies the maximum number
of CA certificates that may follow this CA certificate in the
certification chain. Value "0" means that this CA may only issue
end-entity certificates, but no CA certificates. If the attribute
is not set, there is no limit to the allowed length of the
certification path.
The settings of the basicConstraints extension differ for each
control-plane certificate type. For more information, see the below
sections describing the control-plane and voting certificates:
Section 2.2.2, Section 2.2.3, Section 2.2.4, and Section 2.2.5.
2.2.2. Control-Plane Root Certificate
The control-plane root private key is used to sign control-plane CA
certificates. Consequently, the control-plane root certificate with
the control-plane root public key is used to verify control-plane CA
certificates. So indirectly, CP root certificates determine which
ASes act as CA in an ISD.
In X.509 terms, CP root certificates are self-_signed_ CA
certificates. That is, issuer and subject of the certificate are the
same entity, and the public key in the root certificate can be used
to verify the root certificate's signature. The CP root public key
and proof of ownership of the private key are embedded in the Trust
Root Configuration (TRC) of an Isolation Domain (ISD), via the self-
signed CP root certificate. This facilitates the bootstrapping of
trust within an ISD, and marks the CP root certificates as the
starting point of an ISD's certificate verification path.
All constraints described in Section 2.2.1 also apply to CP root
certificates.
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The recommended *maximum validity period* of a CP root certificate
is: 1 year.
2.2.2.1. Extension Constraints
The extensions of a CP root certificate differ from the general
certificate requirements described previously, in the following ways.
2.2.2.1.1. keyUsage Extension
* digitalSignature attribute: This attribute MUST NOT be set
(because the CP root certificate should not be used to verify
control-plane messages).
* keyCertSign attribute: This attribute MUST be set.
2.2.2.1.2. extKeyUsage Extension
The extKeyUsage extension MUST be present in the CP root certificate.
It must be defined as follows:
* id-kp-serverAuth attribute: MUST NOT be set.
* id-kp-clientAuth attribute: MUST NOT be set.
* id-kp-timeStamping attribute: MUST be set.
Additionally, the id-kp-root attribute must be specified, as follows:
id-kp-root AttributeType ::= {id-ana id-cppki(1) id-kp(3) 3}
where id-ana specifies the root SCION object identifier (OID).
*Note:* The SCION open source implementation currently uses the
Anapaya IANA Private Enterprise Number (55324) as root SCION object
identifier (OID): id-ana ::= OBJECT IDENTIFIER {1 3 6 1 4 1 55324}
2.2.2.1.3. basicConstraints Extension
The basicConstraints extension MUST be present in the CP root
certificate.
The extension attributes must be set as follows:
* cA attribute: MUST be set to TRUE.
* pathLenConstraint attribute: Should be set to "1". Additionally,
it must be marked as "critical", according to X.509
(https://handle.itu.int/11.1002/1000/13031).
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2.2.3. Control-Plane CA Certificate
The control-plane CA private key is used to sign control-plane AS
certificates. Consequently, control-plane CA certificates holding
the control-plane CA public key are used to verify control-plane AS
certificates.
The public key needed to verify the CA certificate is in a CP root
certificate. CA certificates do not bundle the root certificate
needed to verify them. In order to verify a CA certificate, a pool
of root certificates must first be extracted from one or more active
TRCs (as described in Section 4.2.
All constraints described in Section 2.2.1 also apply to control-
plane CA certificates.
The recommended *maximum validity period* of a CP CA certificate is:
11 days.
2.2.3.1. Extension Constraints
The extensions of a CP CA certificate differ from the general
certificate requirements described previously, in the following ways.
2.2.3.1.1. keyUsage Extension
* digitalSignature attribute: This attribute MUST NOT be set
(because the control-plane CA certificate should not be used to
verify control-plane messages).
* keyCertSign attribute: This attribute MUST be set.
2.2.3.1.2. extKeyUsage Extension
The extKeyUsage extension MAY be present in the CP CA certificate.
If the extKeyUsage extension is present in the CP CA certificate, the
attributes id-kp-serverAuth and id-kp-clientAuth MUST NOT be set.
2.2.3.1.3. basicConstraints Extension
The basicConstraints extension MUST be present in the CP CA
certificate.
The extension attributes must be set as follows:
* cA attribute: MUST be set to TRUE.
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* pathLenConstraint attribute: SHOULD be set to "0". This means
that the CP CA certificate can only issue end-entity certificates.
Additionally, the attribute must be marked as "critical",
according to X.509 (https://handle.itu.int/11.1002/1000/13031).
2.2.4. Control-Plane AS Certificate
SCION ASes sign control-plane messages, such as PCBs, with their AS
private key. Consequently, control-plane AS certificates holding the
corresponding AS public key are required to verify control-plane
messages.
In X.509 terms, control-plane AS certificates are end-entity
certificates. That is, they cannot be used to verify other
certificates.
All constraints described in Section 2.2.1 also apply to control-
plane AS certificates.
The recommended *maximum validity period* of a CP AS certificate is:
3 days.
2.2.4.1. Extension Constraints
The extensions of a CP AS certificate differ from the general
certificate requirements described previously, in the following ways.
2.2.4.1.1. keyUsage Extension
* digitalSignature attribute: This attribute MUST be set.
* keyCertSign attribute: This attribute MUST NOT be set.
2.2.4.1.2. extKeyUsage Extension
The extKeyUsage extension MUST be present in the CP AS certificate.
It must be defined as follows:
* id-kp-serverAuth attribute: MUST be set, if the CP AS certificate
is used on the server-side of a control-plane TLS session
establishment.
* id-kp-clientAuth attribute: MUST be set, if the CP AS certificate
is used on the client-side of control-plane TLS session
establishment.
* id-kp-timeStamping attribute: MUST be set.
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2.2.4.1.3. basicConstraints Extension
Control-plane AS certificates should not include the basicConstraints
extension.
2.2.5. Voting Certificates
There are two types of voting certificates: the (1) regular voting
certificates and the (2) sensitive voting certificates. They contain
the public keys associated with the private keys that are allowed to
cast votes in the TRC update process. Voting certificates are
X.509-style certificates.
Regular and sensitive voting certificates are used to verify regular
and sensitive TRC updates, respectively.
The constraints described in Section 2.2.1 also apply to voting
certificates. There is one exception: A voting certificate is not
required to include the ISD-AS number attribute in its distinguished
name (for more information on this attribute, see Section 2.2.1.4.1).
2.2.5.1. Regular Voting Certificate
Regular voting certificates state which keys are allowed to cast
votes in a regular update. In X.509 terms, regular voting
certificates are self-signed end-entity certificates. This means
that the issuer and subject of a regular voting certificate are the
same entity, and the key within the certificate was used to sign the
certificate. However, a regular voting certificate cannot be used to
verify other certificates.
The recommended *maximum validity period* of a regular voting
certificate is: 1 year.
2.2.5.2. Sensitive Voting Certificate
Sensitive voting certificates specify which keys are allowed to cast
votes in a sensitive update. In X.509 terms, sensitive voting
certificates are self-signed end-entity certificates. This means
that the issuer and subject of a sensitive voting certificate are the
same entity, and the key within the certificate was used to sign the
certificate. However, a sensitive voting certificate cannot be used
to verify other certificates.
The recommended *maximum validity period* of a sensitive voting
certificate is: 5 years.
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2.2.5.2.1. Extension Constraints of Voting Certificates
The extensions of both regular and sensitive voting certificates
differ from the general certificate requirements described
previously, in the following ways.
2.2.5.2.1.1. keyUsage Extension
The keyUsage extension is not required in a voting certificate.
However, if this extension is present, both the digitalSignature and
the keyCertSign attributes MUST NOT be set.
2.2.5.2.1.2. extKeyUsage Extension
The extKeyUsage extension MUST be present in a voting certificate.
It must be defined as follows:
* id-kp-serverAuth attribute: MUST NOT be set.
* id-kp-clientAuth attribute: MUST NOT be set.
* id-kp-timeStamping attribute: MUST be set.
Additionally, the id-kp-regular / id-kp-sensitive attribute MUST be
set, as follows:
* For a regular voting certificate:
id-kp-regular AttributeType ::= {id-ana id-cppki(1) id-kp(3) 1}
* For a sensitive voting certificate:
id-kp-sensitive AttributeType ::= {id-ana id-cppki(1) id-kp(3) 1}
where id-ana specifies the root SCION object identifier (OID).
*Note:* The SCION open source implementation currently uses the
Anapaya IANA Private Enterprise Number (55324) as root SCION object
identifier (OID): id-ana ::= OBJECT IDENTIFIER {1 3 6 1 4 1 55324}
2.2.5.2.1.3. basicConstraints Extension
The basicConstraints extension SHOULD NOT be part of a voting
certificate.
However, if this extension is present in a voting certificate, it
MUST be defined as follows:
* cA attribute: MUST be set to FALSE.
* pathLenConstraint attribute: MUST NOT be present.
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3. Specification of the Trust Root Configuration
This section provides an in-depth specification of the trust root
configuration (TRC) file (see Section 3.1). The TRC contains policy
information about an ISD and acts as a distribution mechanism for the
trust anchors of that ISD. It enables securing the control-plane
interactions, and is thus an integral part of the SCION
infrastructure.
The initial TRC of an ISD is signed during a signing ceremony and
then distributed throughout the ISD. This signing ceremony follows
specific rules; Section 3.2 describes these rules.
3.1. TRC Specification
The trust root configuration (TRC) is a signed collection of X.509
(https://handle.itu.int/11.1002/1000/13031) v3 certificates.
Additionally, the TRC contains ISD-specific policies encoded in a
Cryptographic Message Syntax (CMS) [RFC5652] envelope.
The TRC's certificates collection consists of a set of control-plane
root certificates, which build the root of the certification chain
for the AS certificates in an ISD. The other certificates in the TRC
are solely used for signing the next TRC, a process called "voting".
The verification of a new TRC thus depends on the policies and voting
certificates defined in the previous TRC.
*Note:* See Section 2 for the general specifications of SCION's
control-plane certificates, as well as Section 2.2.2 and
Section 2.2.5, for the specifications of the control-plane root
certificates and voting certificates, respectively.
This section provides a detailed specification of the TRC. It
presents the TRC format definitions and describes the TRC payload
fields. The section uses the ITU-T X.680
(https://handle.itu.int/11.1002/1000/14468) syntax.
3.1.1. TRC Types and States
The following types of TRCs exist:
* Initial: The very first TRC of an ISD is the initial TRC of that
ISD. It is a special case of the base TRC, where the number of
the ISD is specified.
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* Base: A base TRC is either the initial TRC, or the first TRC after
a trust reset (see Section 1.3.1). Trust for a base TRC cannot be
inferred by verifying a TRC update; base TRCs are trusted
axiomatically, similarly to how root CA certificates are trusted
by clients in the Web PKI.
* Update: All non-base TRCs are updated TRCs. They are the product
of either a regular or a sensitive update.
A TRC can have the following states:
* Valid: The validity period of a TRC is defined in the TRC itself,
in the validity field (see Section 3.1.2.2.3). A TRC is
considered valid if the current time falls within its validity
period.
* Active: An active TRC is a valid TRC that can be used for
verifying certificate signatures. This is either the latest TRC
or the predecessor TRC, if it is still in its grace period (as
defined in the grace field of the new TRC, see Section 3.1.2.2.4).
No more than two TRCs can be active at the same time for any ISD.
Figure 3 shows the content of both a base/initial TRC and the first
regularly-updated TRC based on the base TRC. All elements of the
shown TRCs are specified in detail in the following subsections.
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+--------------------------------------------+ +--------------------------------------------+
| TRC 1 (base, initial) | | TRC 2 (regular update) |
|+------------------------------------------+| |+------------------------------------------+|
||- Version - Core ASes || ||- Version - Core ASes ||
||- ID - Description || ||- ID - Description ||
||- Validity - No Trust Reset || ||- Validity - No Trust Reset ||
||- Grace Period - Voting Quorum || ||- Grace Period - Voting Quorum ||
||- ... || ||- ... ||
|+------------------------------------------+| |+------------------------------------------+|
|+--------------------++--------------------+| |+--------------------++--------------------+|
||Votes (cert.indices)|| Regular Voting || ||Votes (cert.indices)|| Regular Voting ||
|| || Certificates || || || Certificates ||
|| (empty) || || || (1),(2)... || ||
|| ||+-----+ +-----+ || || ||+-----+ +-----+ ||
|| ||| (1) | | (2) | || || ||| (1) | | (2) | ||
|| |||C | |C | ... || || |||C | |C | ... ||
|| ||| reg | | reg | || || ||| reg | | reg | ||
|+--------------------+|+--+--+ +--+--+ || |+--------------------+|+-----+ +-----+ ||
|+--------------------+| | | || |+--------------------+| ||
|| || | +--------++-----+ || || ||
|| || +----------------++-+ | || || ||
|| Signatures |+--------------------+| | | || Signatures |+--------------------+|
|| |+--------------------+| | | || |+--------------------+|
||+------------------+|| Sensitive Voting || | | ||+------------------+|| Sensitive Voting ||
|||73 A9 4E AO 0D ...||| Certificates || | +--+>|48 AE E4 80 DB ...||| Certificates ||
||+------------------+||+-----+ +-----+ || | ||+------------------+||+-----+ +-----+ ||
||+------------------+||| (3) | | (4) | || | ||+------------------+||| (3) | | (4) | ||
|||53 B7 7C 98 56 ...||||C | |C | || +------+>|7E BC 75 98 25 ...||||C | |C | ||
||+------------------+||| sens| | sens| ... || ||+------------------+||| sens| | sens| ... ||
|| ... ||+-----+ +-----+ || || ... ||+-----+ +-----+ ||
|+--------------------++--------------------+| |+--------------------++--------------------+|
|+------------------------------------------+| |+------------------------------------------+|
|| CP Root Certificates || || CP Root Certificates ||
|| || || ||
|| +-----+ +-----+ +-----+ +-----+ || || +-----+ +-----+ +-----+ +-----+ ||
|| | (5) | | (6) | | (7) | | (8) | || || | (5) | | (6) | | (7) | | (8) | ||
|| |C | |C | |C | |C | || || |C | |C | |C | |C | ||
|| | root| | root| | root| | root| ..... || || | root| | root| | root| | root| ..... ||
|| +-----+ +-----+ +-----+ +-----+ || || +-----+ +-----+ +-----+ +-----+ ||
|+------------------------------------------+| |+------------------------------------------+|
+--------------------------------------------+ +--------------------------------------------+
Figure 3: The TRC on the left-hand side is the initial base TRC.
The TRC on the right is the product of the first regular update
of the base TRC.
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3.1.2. TRC Format
The trust root configuration (TRC) of an ISD defines the roots of
trust of the ISD, and builds the base of the ISD's control-plane PKI.
It holds the root and voting certificates of the ISD and defines the
ISD's trust policy.
3.1.2.1. TRC Schema
The following code block shows the format of a TRC specification file
(the payload schema):
TRCPayload ::= SEQUENCE {
version TRCFormatVersion,
iD TRCID,
validity Validity,
gracePeriod INTEGER,
noTrustReset BOOLEAN DEFAULT FALSE,
votes SEQUENCE OF INTEGER (SIZE (1..255)),
votingQuorum INTEGER (1..255),
coreASes SEQUENCE OF ASN,
authoritativeASes SEQUENCE OF ASN,
description UTF8String (SIZE (0..1024)),
certificates SEQUENCE OF Certificate }
TRCFormatVersion ::= INTEGER { v1(0) }
TRCID ::= SEQUENCE {
iSD ISD,
serialNumber INTEGER (1..MAX),
baseNumber INTEGER (1..MAX) }
ISD ::= INTEGER (1..65535)
Validity ::= SEQUENCE {
notBefore Time,
notAfter Time }
ASN ::= INTEGER (1..281474976710655)
The TRCPayload sequence contains the identifying information of a TRC
as well as policy information for TRC updates. Furthermore, it
defines the list of certificates that build the trust anchor of the
ISD.
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For signature calculation, the data that is to be signed is encoded
using ASN.1 distinguished encoding rules (DER) X6.90
(https://handle.itu.int/11.1002/1000/14472). For more details, see
Section 3.1.3.
3.1.2.2. TRC Fields
This section describes the syntax and semantics of all TRC payload
fields.
3.1.2.2.1. version Field
The version field describes the version of the TRC format
specification.
Currently, the version MUST always be "v1".
3.1.2.2.2. iD Field
The iD field specifies the unique identifier of the TRC.
The identifier is a unique sequence of
* ISD number (iSD attribute),
* base number (baseNumber attribute), and
* TRC serial number (serialNumber attribute).
All numbers MUST be positive integers.
* The *ISD number* MUST be an integer in the inclusive range between
1 and 65535 (i.e., the ISD numbering range).
* The *base number* indicates the starting point of the current TRC
update chain. This starting point is either the ISD's initial TRC
or the currently valid base TRC, if the valid base TRC differs
from the initial TRC. The latter MUST be the case after a trust
reset.
* The *serial number* represents the current update cycle, counting
from the initial TRC of a specific ISD.
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A TRC where the base number is equal to the serial number is a base
TRC. The initial TRC is a special case of a base TRC. An ISD's
initial TRC MUST have a serial number of 1 and a base number of 1.
With every TRC update, the serial number MUST be incremented by one.
This facilitates uniquely identifying the predecessor and successor
TRC in a TRC update chain.
If a trust reset is necessary, a new base TRC is announced, in order
to start a new and clean TRC update chain. The base number of this
new TRC update chain SHOULD be the number following the serial number
of the latest TRC that was produced by a non-compromised TRC update
for this ISD.
*Example*
The following simple example illustrates how to specify the ID of the
TRCs in an TRC update chain for _ISD 14_. The IDs are given in a
human-readable notation, where Bxx is the base number, and Sxx the
serial number.
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+===========+=================+====================================+
| Update | TRC ID | Remarks |
+===========+=================+====================================+
| Initial | ISD14-B01-S01 | |
+-----------+-----------------+------------------------------------+
| Regular | ISD14-B01-S02 | Only the serial number is |
| | | incremented. |
+-----------+-----------------+------------------------------------+
| Regular | ISD14-B01-S03 | Only the serial number is |
| | | incremented. |
+-----------+-----------------+------------------------------------+
| Sensitive | ISD14-B01-S04 | Only the serial number is |
| | | incremented. |
+-----------+-----------------+------------------------------------+
| Trust | ISD14-*B05*-S05 | A trust reset includes the |
| reset | | creation of a new base TRC. The |
| | | new base number follows the serial |
| | | number "04" of the latest TRC |
| | | resulting from a non-compromised |
| | | TRC update for this ISD. |
+-----------+-----------------+------------------------------------+
| Regular | ISD14-B05-S06 | Only the serial number is |
| | | incremented. |
+-----------+-----------------+------------------------------------+
| Regular | ISD14-B05-S07 | Only the serial number is |
| | | incremented. |
+-----------+-----------------+------------------------------------+
| And so on | | |
+-----------+-----------------+------------------------------------+
Table 3: ID of TRCs in TRC update chain
3.1.2.2.3. validity Field
The validity field defines the validity period of the TRC. This is
the period of time during which the TRC is in the "valid" state. The
notBefore and notAfter attributes of the validity field specify the
lower and upper bound of the time interval during which a TRC can be
active.
*Note:* An active TRC is a valid TRC that can be used for verifying
certificate signatures. The time period during which a TRC is active
can be shorter than the time period during which the TRC is valid.
For more information, see Section 3.1.1.
The validity field consists of a sequence of two dates, as defined in
section 7.2. of X.509 (https://handle.itu.int/11.1002/1000/13031).
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In addition to this standard definition, the following constraint
applies to the validity field of the TRC used in SCION:
* All TRCs MUST have a well-defined expiration date. SCION
implementations MUST NOT create TRCs that use the
"99991231235959Z" generalized time value, and verifiers MUST error
out when encountering such a TRC.
3.1.2.2.4. gracePeriod Field
The gracePeriod field of a TRC specifies the period of time during
which the predecessor TRC can still be considered active (the "grace
period"). The grace period starts at the beginning of the validity
period of the new TRC.
The validity period of the predecessor TRC ends when
* the grace period has passed,
* the predecessor's expiration time is reached, or
* the successor TRC of the new TRC has been announced.
*Note:* The event that happens first marks the end of the
predecessor's validity period.
The gracePeriod field defines the grace period as a number of seconds
(positive integer).
The value of the gracePeriod field in a base TRC MUST be zero. The
value of the gracePeriod field in a non-base TRC SHOULD be non-zero.
It should be long enough to provide sufficient overlap between the
TRCs in order to facilitate interruption-free operations in the ISD.
If the grace period is too short, some control-plane AS certificates
might expire before the corresponding AS can fetch an updated version
from its CA.
3.1.2.2.5. noTrustReset Boolean
The noTrustReset Boolean specifies whether a trust reset is forbidden
by the ISD. Within a TRC update chain, this value CANNOT be changed
by a regular or sensitive update. However, it is possible to change
the noTrustReset value in the event of a trust reset, where a new
base TRC is created.
The noTrustReset field is optional and defaults to FALSE.
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*Important:* Note that once the noTrustReset Boolean is set to TRUE
and a trust reset is disallowed, this cannot be reversed. Therefore,
ISDs SHOULD always set this value to FALSE, unless they have
sufficiently assessed the risks and implications of making a trust
reset impossible.
*Note:* A trust reset represents a special use case where a new base
TRC is created. It therefore differs from a TRC update (regular or
sensitive), as the signatures in the new base TRC cannot be verified
with the certificates contained in the predecessor TRC. Instead, a
trust reset base TRC must be axiomatically trusted, similarly to how
the initial TRC is trusted.
3.1.2.2.6. votes Field
The votes field contains a sequence of indices that refer to the
voting certificates in the predecessor TRC. If index i is part of
the votes field, then the voting certificate at position i in the
certificates sequence of the predecessor TRC casted a vote on the
successor TRC.
*Note:* In a base TRC, the votes sequence is empty.
Every entry in the votes sequence MUST be unique.
Further restrictions on votes are discussed in Section 3.1.5.
*Note:* The votes sequence of indices is mandatory in order to
prevent stripping voting signatures from the TRC. Absence of the
votes sequence makes it possible to transform a TRC with more voting
signatures than the Section 3.1.2.2.7 into multiple verifiable TRCs
with the same payload, but different voting signature sets. This
would violate the requirement of uniqueness of a TRC.
3.1.2.2.7. votingQuorum Field
The votingQuorum field defines the number of necessary votes on a
successor TRC to make it verifiable.
A voting quorum greater than one will prevent a single entity from
creating a malicious TRC update.
3.1.2.2.8. coreASes Field
The coreASes field contains the AS numbers of the core ASes in this
ISD.
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Each core AS number MUST be unique in the sequence of core AS
numbers. That is, each AS number must appear only once in the
coreASes field.
3.1.2.2.8.1. Revoking or Assigning Core Status
* To revoke the core status of a given AS, remove the respective AS
number from the sequence of AS numbers in the coreASes field.
* To assign the core status to a given AS, add the respective AS
number to the sequence of AS numbers in the coreASes field.
*Important:* Revoking or assigning the core status of/to an AS always
requires a (sensitive) TRC update.
3.1.2.2.9. authoritativeASes Field
The authoritativeASes field contains the AS numbers of the
authoritative ASes in this ISD.
Authoritative ASes are those ASes in an ISD that always have the
latest TRCs of the ISD. As a consequence, authoritative ASes also
start the announcement of a TRC update.
* Every authoritative AS MUST be a core AS and be listed in the
coreASes field.
* Each authoritative AS number MUST be unique in the sequence of
authoritative AS numbers. That is, each AS number must appear
only once in the authoritativeASes field.
3.1.2.2.9.1. Revoking or Assigning Authoritative Status
* To revoke the authoritative status of a given AS, remove the
respective AS number from the sequence of AS numbers in the
authoritativeASes field.
* To assign the authoritative status to a given AS, add the
respective AS number to the sequence of AS numbers in the
authoritativeASes field.
*Important:* Revoking or assigning the authoritative status of/to an
AS always requires a (sensitive) TRC update.
3.1.2.2.10. description Field
The description field contains a UTF-8 encoded string that describes
the ISD.
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* The description field SHOULD NOT be empty.
* The description of the ISD MUST be in English. Additionally, the
description field MAY contain information in other languages.
3.1.2.2.11. certificates Field
The voting ASes and the certification authorities (CAs) of an ISD are
not specified explicitly in the ISD's TRC. Instead, this information
is defined by the list of voting and root certificates in the
certificates field of the TRC payload.
The certificates field is a sequence of self-signed X.509
certificates. Each certificate in the certificate sequence must be
one of the following types:
* a sensitive voting certificate,
* a regular voting certificate, or
* a CP root certificate.
*Note:* The listing location of a certificate within the TRC
corresponds with the certificate's type.
A certificate that is no control-plane root or voting certificate
MUST NOT be included in the sequence of certificates in the
certificates field.
The constraints on these certificates are described in Section 2.2.2
and Section 2.2.5, respectively. Additionally, the following
constraints MUST hold for each certificate:
* Each certificate MUST be unique in the sequence of certificates.
That is, each certificate must appear only once in the
certificates field.
* The issuer / serialNumber pair for each certificate MUST be
unique.
* If an ISD-AS number is present in the distinguished name of the
certificate, the ISD number in the certificate MUST be equal to
the ISD number of this TRC (which is defined in the iD field (see
Section 3.1.2.2.2).
* Every certificate MUST have a validity period that fully contains
the validity period of this TRC. That is, the notBefore date of
this TRC's validity period MUST be equal to or later than the
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certificate's notBefore date, and the notAfter date of this TRC's
validity period MUST be before or equal to the certificate's
notAfter date.
* Per certificate type, every certificate distinguished name MUST be
unique.
The following must hold for the entire sequence of certificates in
the certificates field:
* votingQuorum <= count (sensitive voting certificates)
That is, the quorum defined in the TRC's votingQuorum field
(Section 3.1.2.2.7) must be smaller than or equal to the number of
_sensitive_ voting certificates specified in the TRC's
certificates field.
* votingQuorum <= count (regular voting certificates)
That is, the quorum defined in the TRC's votingQuorum field
(Section 3.1.2.2.7) must be smaller than or equal to the number of
_regular_ voting certificates specified in the TRC's certificates
field.
3.1.3. TRC Signature Syntax
A TRC contains policy information about an ISD and acts as a
distribution mechanism for the trust anchors of that ISD. Each TRC
(payload) is digitally signed. The syntax used to sign and
encapsulate the TRC payload is the Cryptographic Message Syntax
(CMS), as defined in [RFC5652]. The signed TRC payload is of the CMS
signed-data content type, as defined in Section 5 of [RFC5652], and
encapsulated in a CMS ContentInfo element, as defined in Section 3 of
[RFC5652].
The following code block displays the general syntax definitions of
the Cryptographic Message Syntax:
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ContentInfo ::= SEQUENCE {
contentType ContentType,
content [0] EXPLICIT ANY DEFINED BY contentType }
ContentType ::= OBJECT IDENTIFIER
SignedData ::= SEQUENCE {
version CMSVersion,
digestAlgorithms DigestAlgorithmIdentifiers,
encapContentInfo EncapsulatedContentInfo,
certificates [0] IMPLICIT CertificateSet OPTIONAL,
crls [1] IMPLICIT RevocationInfoChoices OPTIONAL,
signerInfos SignerInfos }
DigestAlgorithmIdentifiers ::= SET OF DigestAlgorithmIdentifier
SignerInfos ::= SET OF SignerInfo
EncapsulatedContentInfo ::= SEQUENCE {
eContentType ContentType,
eContent [0] EXPLICIT OCTET STRING OPTIONAL }
SignerInfo ::= SEQUENCE {
version CMSVersion,
sid SignerIdentifier,
digestAlgorithm DigestAlgorithmIdentifier,
signedAttrs [0] IMPLICIT SignedAttributes OPTIONAL,
signatureAlgorithm SignatureAlgorithmIdentifier,
signature SignatureValue,
unsignedAttrs [1] IMPLICIT UnsignedAttributes OPTIONAL }
SignerIdentifier ::= CHOICE {
issuerAndSerialNumber IssuerAndSerialNumber,
subjectKeyIdentifier [0] SubjectKeyIdentifier }
SignedAttributes ::= SET SIZE (1..MAX) OF Attribute
UnsignedAttributes ::= SET SIZE (1..MAX) OF Attribute
Attribute ::= SEQUENCE {
attrType OBJECT IDENTIFIER,
attrValues SET OF AttributeValue }
AttributeValue ::= ANY
SignatureValue ::= OCTET STRING
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SCION implementations have to fulfil the following additional rules,
on top of the general syntax rules from [RFC5652]:
* EncapsulatedContentInfo sequence:
- The eContentType field must be set to "id-data".
- The content of the eContent field must be the DER-encoded TRC
payload. This has the benefit that the format is backwards
compatible with PKCS #7, as described in Section 5.2.1 of
[RFC5652].
* SignedData sequence:
- The certificates field of the CMS syntax definitions MUST be
left empty. The certificate pool used to verify a TRC update
is already specified in the certificates field of the
predecessor TRC's payload (see also Section 3.1.2.2.11).
- The version field MUST be set to "1". This is because SCION
uses the "id-data" content type to encapsulate content info,
and does not specify any certificate in the SignedData sequence
(see also Section 5.1 of [RFC5652]).
* SignerIdentifier choice:
- The type of signer identifier selected here MUST be
IssuerAndSerialNumber.
* SignerInfo sequence:
- The version field MUST be set to "1". This is because SCION
uses the "IssuerAndSerialNumber" type of signer identifier (see
also Section 5.3 of [RFC5652]).
- The algorithm specified in the signatureAlgorithm field MUST be
one of the supported algorithms (see also Section 2.2.1.3).
- The digestAlgorithm is determined by the algorithm specified in
the signatureAlgorithm field.
3.1.3.1. TRC Equality
The signer infos in the signed TRC are part of an unordered set, per
[RFC5652]. This implies that the signer infos can be reordered
without affecting verification. Certain operations, however, require
TRCs to be equal according to the following equality definition:
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*Two TRCs are equal, if and only if their payloads are byte equal.*
This definition of equality is sufficient, because the TRC payload
exactly defines which signatures must be attached in the signed TRC:
* The required signatures from voting certificates are explicitly
mentioned in the votes field of the payload: If index "i" is part
of the votes field, then the voting certificate at position i in
the certificates sequence of the predecessor TRC casted a vote on
the successor TRC. See also Section 3.1.2.2.6.
* The required signatures for new certificates are implied by the
currently valid TRC payload, and, in case of a TRC update, the
predecessor payload.
3.1.4. Control-Plane Certification Path
The certification path of a control-plane AS certificate starts in a
control-plane root certificate. The control-plane root certificates
for a given ISD are distributed via the TRC.
To be able to validate the certification path, the relying party must
build a trust anchor pool, which consists of a set of control-plane
root certificates from the available TRCs. Based on this pool, the
relying party can select candidate certification paths and verify
them.
3.1.4.1. Trust Anchor Pool - TRC Selection
The selection of the right set of TRCs to build the trust anchor pool
depends on the time of verification. The trust anchor pool is
usually used to verify control-plane messages. In this case, the
time of verification is the current time. However, if the trust
anchor pool will be used for auditing, the time of verification is
the point in time for which you want to check whether a given
signature was verifiable.
The selection algorithm for building the trust anchor pool is
described in pseudo-python code below.
def select_trust_anchors(trcs: Dict[(int,int), TRC], verification_time: int) -> Set[RootCert]:
"""
Args:
trcs: The dictionary mapping (serial number, base number) to the TRC for a given ISD.
verification_time: The time of verification.
Returns:
The set of CP Root certificates that act as trust anchors.
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"""
# Find highest base number that has a TRC with a validity period
# starting before verification time.
base_nr = 1
for trc in trcs.values():
if trc.id.base_nr > base_nr and trc.validity.not_before <= verification_time:
base_nr = trc.id.base_nr
# Find TRC with highest serial number with the given base number and a
# validity period starting before verification time.
serial_nr = 1
for trc in trcs[isd].values():
if trc.id.base_nr != base_nr:
continue
if trc.id.serial_nr > serial_nr and trc.validity.not_before <= verification_time:
serial_nr = trc.id.serial_nr
candidate = trcs[(serial_nr, base_nr)]
# If the verification time is not inside the validity period,
# there is no valid set of trust anchors.
if not candidate.validity.contains(verification_time):
return set()
# If the grace period has passed, only the certificates in that TRCs
# may be used as trust anchors.
if candidate.validity.not_before + candidate.grace_period < verification_time:
return collect_trust_anchors(candidate)
predecessor = trcs.get((serial_nr-1, base_nr))
if not predecessor or predecessor.validity.not_after < verification_time:
return collect_trust_anchors(candidate)
return collect_trust_anchors(candidate) | collect_trust_anchors(predecessor)
def collect_trust_anchors(trc: TRC) -> Set[RootCert]:
"""
Args:
trc: A TRC from which the CP Root Certificates shall be extracted.
Returns:
The set of CP Root certificates that act as trust anchors.
"""
roots = set()
for cert in trc.certificates:
if not cert.basic_constraints.ca:
continue
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roots.add(cert)
return roots
3.1.5. TRC Updates
All non-base TRCs of an ISD are updates of the ISD's base TRC(s).
The TRC update chain consists of regular and sensitive TRC updates.
Based on the type of update, a different set of voters is necessary
to create a verifiable TRC update. The type of update also
determines the (payload) information that changes in the updated TRC.
This section describes the rules that apply to updating a TRC in
regard to the payload information contained in the TRC. Some rules
are valid for both update types, some only apply to a regular or a
sensitive TRC update, respectively.
3.1.5.1. Changed or New Certificates
In the context of a TRC update,
* A certificate is _changing_, if the certificate is part of the
certificates sequence in the predecessor TRC, but no longer part
of the certificates sequence in the updated TRC. Instead, the
certificates sequence of the updated TRC holds another certificate
of the _same type_ and with the _same distinguished name_.
* A certificate is _new_, if there is *no* certificate of the same
type and distinguished name at all in the certificates sequence of
the predecessor TRC.
*Note:* Every new sensitive or regular voting certificate in a TRC
attaches a signature to the TRC. This is done to ensure that the
freshly included voting entity agrees with the contents of the TRC it
is now part of.
3.1.5.2. Update Rules - Overview
The following table gives an overview of the types of TRC update as
well as the rules that must apply in regard to the updated TRC's
payload information.
The sections that follow provide more detailed descriptions of each
rule.
+===========+===================+==============+====================+
| Type of | Payload Updated | Payload | Payload Updated |
| Update | TRC - Unchanged | Updated TRC | TRC: Other |
| | Elements | - Required | Rules to Hold |
| | | Changes | |
+===========+===================+==============+====================+
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| Both | - iD field: iSD | iD field: | votes field: |
| Regular | and baseNumber | serialNumber | Nr. of votes |
| AND | | MUST be | (indices) >= |
| Sensitive | | incremented | nr. in the |
| Updates | | by 1 | votingQuorum |
| | | | field of the |
| | | | predecessor TRC |
+-----------+-------------------+--------------+--------------------+
| | - noTrustReset | | |
| | field | | |
+-----------+-------------------+--------------+--------------------+
+-----------+-------------------+--------------+--------------------+
| Regular | - Quorum in the | | votes field: |
| TRC | votingQuorum | | |
| Update | field | | |
+-----------+-------------------+--------------+--------------------+
| | - Core ASes in | | - All votes |
| | the coreASes | | must only refer |
| | field | | to _regular_ |
| | | | voting |
| | | | certificates in |
| | | | the predecessor |
| | | | TRC |
+-----------+-------------------+--------------+--------------------+
| | - ASes in the | | - Must include |
| | authoritativeASes | | votes of each |
| | field | | changed regular |
| | | | voting |
| | | | certificate |
| | | | from the |
| | | | predecessor TRC |
+-----------+-------------------+--------------+--------------------+
| | - Nr. and | | signatures |
| | distinguished | | field: |
| | names of root & | | |
| | voting | | |
| | certificates in | | |
| | the certificates | | |
| | field | | |
+-----------+-------------------+--------------+--------------------+
| | - Set of | | - Must include |
| | sensitive voting | | signatures of |
| | certificates in | | each changed |
| | the certificates | | root |
| | field | | certificate |
| | | | from the |
| | | | predecessor TRC |
+-----------+-------------------+--------------+--------------------+
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+-----------+-------------------+--------------+--------------------+
| Sensitive | If the update | | votes field: |
| TRC | does not qualify | | |
| Update | as a regular | | |
| | update, it is a | | |
| | sensitive update | | |
+-----------+-------------------+--------------+--------------------+
| | | | - All votes |
| | | | must only refer |
| | | | to _sensitive_ |
| | | | voting |
| | | | certificates in |
| | | | the predecessor |
| | | | TRC |
+-----------+-------------------+--------------+--------------------+
Table 4: Overview of the update types and corresponding rules
3.1.5.3. General Update Rules
The following rules MUST hold for each updated TRC, independent of
the update type:
* The iSD and baseNumber in the iD field MUST NOT change (see also
Section 3.1.2.2.2).
* The serialNumber in the iD field MUST be incremented by one.
* The noTrustReset field MUST NOT change (see also
Section 3.1.2.2.5).
* The votes sequence of the updated TRC MUST only contain indices
that refer to sensitive or regular voting certificates in the
predecessor TRC. This guarantees that the updated TRC only
contains valid votes authenticated by sensitive or regular voting
certificates in the predecessor TRC. For more information, see
Section 3.1.2.2.6 and Section 3.1.2.2.11.
* The number of votes in the updated TRC MUST be greater than or
equal to the number set in the votingQuorum field of the
predecessor TRC (see Section 3.1.2.2.7). The number of votes
corresponds to the number of indices in the votes field of the
updated TRC.
3.1.5.4. Regular TRC Update
A regular TRC update is a periodic re-issuance of the TRC where the
entities and policies listed in the TRC remain unchanged.
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A TRC update qualifies as a regular update, if the following rules
apply in regard to the TRC's payload information.
* The settings of the following fields in the updated TRC MUST
remain the same compared to the predecessor TRC:
- The voting quorum set in the votingQuorum field.
- The core ASes specified in the coreASes field.
- The authoritative ASes specified in the authoritativeASes
field.
- The number of sensitive and regular voting certificates as well
as CP root certificates included in the certificates field, and
their distinguished names.
- The set of sensitive voting certificates specified in the
certificates field.
* For every regular voting certificate that changes, the regular
voting certificate in the predecessor TRC is part of the voters on
the updated TRC. That is, for each changed regular voting
certificate, an index in the votes field of the updated TRC MUST
refer to the changed regular voting certificate in the predecessor
TRC.
* For every CP root certificate that changes, the CP root
certificate in the predecessor TRC MUST attach a signature to the
signed updated TRC.
* In order for a regular TRC update to be verifiable, all votes MUST
be cast by _regular_ voting certificates. That is, each index in
the votes field of the regularly updated TRC MUST refer to a
_regular_ voting certificate in the certificates field of the
predecessor TRC.
3.1.5.5. Sensitive TRC Update
If a TRC update does not qualify as a regular update, it is
considered a sensitive update.
* In order for a sensitive update to be verifiable, all votes MUST
be cast by _sensitive_ voting certificates. That is, each index
in the votes field of the sensitively updated TRC MUST refer to a
_sensitive_ voting certificate in the certificates field of the
predecessor TRC.
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3.1.5.6. TRC Update Verification
To verify a TRC update, the relying party must perform the following
checks:
* Check that the specified update rules as described above are
respected.
* Check whether the update is regular or sensitive.
- In case of a regular update,
o check that signatures for the changing certificates are
present and verifiable, and
o check that all votes are cast by a regular voting
certificate.
- In case of a sensitive update, check that all votes are cast by
a sensitive voting certificate.
* In both cases, check that all signatures are verifiable, and no
superfluous signatures are attached.
If one or more of the above checks gives a negative result, the
updated TRC should be rejected.
3.2. TRC Signing Ceremony
The very first base TRC of an ISD, called the initial TRC, is a
special case of the base TRC where the number of the ISD is chosen.
The initial TRC must be signed during a signing ceremony--all voting
representatives of the initial TRC need to take part in this signing
ceremony to sign the agreed-upon TRC. As part of the ceremony, the
public keys of all voters are exchanged. The TRC is then distributed
throughout the ISD. All entities within an ISD can initially obtain
an authentic TRC, by means of a secure off- or online mechanism.
Section 3.2.2 describes a possible procedure for the signing ceremony
of an ISD's initial TRC. It is in principle up to the initial
members of an ISD how to shape the signing ceremony. However, it is
recommended having a process in line with the below described
ceremony.
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3.2.1. Non-Base TRC Updates
A non-base TRC is the result of a TRC update, either regular or
sensitive. Only a predefined quorum of voters needs to partake in a
non-base TRC signing ceremony. This is defined in the votingQuorum
field of the predecessor TRC (see Section 3.1.2.2.7). Depending on
the kind of update, these voters represent regular or sensitive
voting certificates, respectively. Furthermore, if one or more _new_
certificates are added to the updated TRC, the corresponding voting
representatives must also join the signing ceremony. For the
distinction between changed and new certificates in a TRC update, see
Section 3.1.5.1.
During the signing ceremony of an updated TRC, it may be necessary to
cast votes with both old and new keys: Voters representing regular or
sensitive voting certificates already present in the predecessor TRC
must cast their votes on the payload file of the updated TRC; the
purpose of signing a TRC with keys contained in the previous TRC is
to certify the update. Furthermore, if previously non-included
voting certificates are added to the TRC, the corresponding voting
representatives must show that they have access to the private keys
listed in these fresh certificates. This is called "showing proof-
of-possession", and done by signing the TRC with the respective
private key.
The ISD members decide themselves about the updating procedure. Some
ISDs will make a distinction between regular and sensitive updates.
These ISDs divide the regular and sensitive signing keys in different
security classes and act accordingly. For example, they keep the
regular key in an online vault while the sensitive key would be
stored offline in cold storage. This way, the regular TRC update
would lend itself to being automated (since the keys are accessible
online) whereas the sensitive one would require manual actions to
access the offline key. Other ISDs, however, keep both regular and
sensitive keys online and perform both updates automatically.
3.2.2. TRC Signing Ceremony - Base TRC
The following sections describe a possible signing ceremony for the
first (initial) base TRC of an ISD. Although each ISD is free to
decide how to shape this signing ceremony, it is recommended
establishing a procedure similar to the one below.
3.2.2.1. Ceremony Participants
A signing ceremony includes participants from member organizations of
the respective Isolation Domain. The participants of the signing
ceremony fulfil different roles:
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* The *ceremony administrator* is in charge of moderating the
signing process. He/she guides all participants through the steps
they need to take. The ceremony administrator may also act as an
intermediary between participants when they share information with
each other.
* A *voting AS representative* is capable of creating voting
signatures on the TRC. This means the voting representative is in
possession of a device with the private keys of the respective
certificates in the TRC.
* A *witness* is any person that participates in the ceremony as a
passive entity. The witness has no active role in any of the
steps of the ceremony, but can stop the process and inquire for
more information if they feel the integrity of the process might
have been compromised.
*Note:* It is assumed that the member organizations of the ISD have
decided in advance, before the signing ceremony, on the roles of the
ceremony participants. That is, they have reached agreement about
the Certificate Authority (CA) ASes, the voting ASes, the
representatives of the voting ASes, the ceremony administrator and
the witnesses.
*Note:* For the signing ceremony, it is assumed that all parties are
trustworthy. Issues encountered during the ceremony are assumed to
be caused by honest mistakes, and not by malicious intent. Hash
comparison checks are included to counter mistakes, such that every
participant is sure that they operate on the same data. Furthermore,
the private keys of each participant never leave their machine. The
ceremony administrator does not have to be entrusted with private
keys.
3.2.2.2. Ceremony Preparations
Prior to the ceremony, participants decide on the physical location
of the ceremony, the devices that will be used during the ceremony
and the policy of the ISD. Specifically, the voting entities agree
on the following parameters:
* validity of the TRC,
* voting quorum,
* core ASes/authoritative ASes,
* description, and
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* list of CP root certificates.
When these values are agreed upon, a number of voters, equal to or
larger than the specified voting quorum, needs to execute the signing
ceremony. For the base TRC, all voting entities need to be present
with both their sensitive and regular voting keys. The ceremony
process is structured in multiple rounds of data sharing. The
ceremony administrator leads the interaction and gives instructions
to each participant.
3.2.2.2.1. Location
The location must provide electricity and enough power sockets for
each participant. Furthermore, it should provide a monitor (or
projector) that allows the ceremony administrator to screen cast.
3.2.2.2.2. Devices
Each party brings their own device that is provisioned with the
required material, as described below.
* Device to exchange data. This device can either be provided by
the ceremony administrator, or, if preferable, by any of the
voting representatives.
* Ceremony administrator's device: The ceremony administrator should
bring a machine that is capable of creating and verifying a TRC.
Furthermore, it needs to be able to compute the SHA-512 digest
(hash value) of files.
* Voting representative's device: The voting representative should
bring a machine that is capable of signing and verifying TRCs.
Thus, the machine needs to have access to all the voting private
keys. Furthermore, it needs to be able to compute the SHA-512
digest (hash value) of the files. The exact binaries that are
required are described in a separate document.
*Important:* It is very important that all devices, especially the
data exchange device, are not compromised. Therefore, the ceremony
should ideally include a procedure to verify that the devices are
secure.
3.2.2.2.3. Preparation Steps
Each party involved in a TRC signing ceremony must go through a few
steps in preparation for the ceremony. This section outlines these
steps.
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3.2.2.2.3.1. Preparatory Tasks of the Ceremony Administrator
In the preparation phase of the TRC Signing Ceremony, the ceremony
administrator has the following tasks:
1. Send out the high-level TRC Signing Ceremony description and the
document describing the TRC Signing Ceremony Phases to the
participants, all in digital form.
2. Remind all representatives of the voting ASes that they need to
agree on a common TRC policy before scheduling the TRC ceremony.
3. Bring all digitally distributed documents as a printout for all
parties that take part.
3.2.2.2.3.2. Preparatory Tasks of the Voting AS Representatives
The preparatory task of the representatives of the voting ASes
(short: the voters) is to generate the necessary certificates.
*Important:* Before generating the certificates, all voters need to
agree on a preliminary TRC policy, in particular on the *validity
period of the TRC*. This is necessary because all the certificates
that are generated in advance must *cover the full TRC validity
period*. The other policy values could be amended during the ceremony
itself.
Each representative of a voting AS must create the following keys and
certificates:
* A sensitive voting private key, and a certificate holding the
corresponding public key.
* A regular voting private key, and a certificate holding the
corresponding public key.
Each representative of an AS that will be a Certificate Authority
must create the following key and certificate:
* A control-plane root private key, and a certificate holding the
corresponding public key.
3.2.2.3. Ceremony Process
The ceremony process for the initial base TRC is structured in
multiple rounds of data sharing. The ceremony administrator leads
the interaction and instructs each participant with what to do.
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The ceremony process contains the following phases:
* Phase 1: Certificate Exchange (Section 3.2.2.3.1). In the first
phase of the ceremony, all voting parties share the certificates
that must be part of the TRC with the ceremony administrator.
* Phase 2: Generation of the TRC Payload (Section 3.2.2.3.2). In
the second phase, the ceremony administrator generates the TRC
payload based on the bundled certificates and the agreed-upon ISD
policy.
* Phase 3: TRC Signing (Section 3.2.2.3.3). In the third phase,
each voting representative attaches the required signatures to the
TRC.
* Phase 4: TRC Validation (Section 3.2.2.3.4). In the final phase
of the ceremony, all voting representatives share the signed TRC
with the ceremony administrator, who aggregates it in a single
signed TRC document.
A detailed description of each phase follows below.
3.2.2.3.1. Phase 1: Certificate Exchange
In Phase 1 of the signing ceremony, all parties share the
certificates that must be part of the TRC with the ceremony
administrator. For the representatives of the voting ASes, these are
the sensitive and the regular voting certificates. For the
representatives of the ASes that are also Certificate Authorities,
the list of certificates must include the CP root certificate.
The actual sharing happens over the data exchange device, which goes
from one voting representative to the next. Each voting
representative copies the requested certificates from their own
machine onto the data exchange device, before forwarding the device
to the next voter. The last voter returns the device to the ceremony
administrator.
*Important:* Note that only the *certificates* must be shared during
this step, *not* the private keys. Copying a private key by mistake
invalidates the security of the ceremony.
For each provided certificate, the ceremony administrator checks that
its validity period covers the previously agreed-upon TRC validity,
that the signature algorithms are correct, and that the certificate
is of the valid type (root, sensitive voting or regular voting
certificate). If the results of these checks are as expected, the
ceremony administrator computes the SHA256 sum for each certificate.
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The ceremony administrator then aggregates and bundles the provided
certificates, and calculates the hash value (SHA-512 digest) over the
entire bundle. Additionally, the ceremony administrator displays all
hash values on the monitor.
The ceremony administrator now shares the bundle with all voters.
This could happen again via the data exchange device, which goes from
one voter to the next. Each voting representative verifies that the
certificates they contributed have the same hash value as the
displayed value on the monitor. Furthermore, all voting
representatives must confirm that the hash value of the bundled
certificates on their machine is equal to the value on the monitor.
Phase 1 is concluded when every voting representative has confirmed
that the SHA256 sums are correct.
*Note:* If there is a mismatch in any of the SHA256 sums, Phase 1
needs to be repeated.
3.2.2.3.2. Phase 2: Generation of the TRC Payload
In Phase 2 of the ceremony, the ceremony administrator generates the
TRC payload based on the bundled certificates and the agreed-upon ISD
policy. The result is displayed on the monitor along with a hash
value (SHA-512 digest).
To be able to generate the payload, the ceremony administrator must
ask the voting representatives for
* The ISD number of the ISD. The number (identifier, ID) of an ISD
must be chosen and agreed upon by the participants during the
signing ceremony of the ISD's initial TRC. The ceremony
administrator needs the ISD number to specify the identifier (ID)
of the initial TRC. This iD is part of the TRC payload. For more
information, see Section 3.1.2.2.2.
* The description of the TRC. For more information, see
Section 3.1.2.2.10.
* The AS numbers of the core ASes of the ISD. For more information,
see Section 3.1.2.2.8.
* The AS numbers of the authoritative ASes of the ISD. For more
information, see Section 3.1.2.2.9.
* The voting quorum for the next TRC update. For more information,
see Section 3.1.2.2.7.
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* The validity period of the new TRC. For more information, see
Section 3.1.2.2.3.
*Note:* It is assumed that the voting ASes have agreed on the answers
to the above questions in advance, before the signing ceremony.
The ceremony administrator can now specify the TRC payload variables
in the payload template file, and show the filled-in template on the
monitor. When the voters have verified the data, the ceremony
administrator can compute the DER encoding of the TRC data as well as
the SHA256 sum of the TRC payload file. The ceremony administrator
then distributes the TRC payload (via the data exchange device) to
all voting representatives, who verify the payload's hash value. The
voters do this by computing the hash value of the TRC payload on
their machine and checking whether their value matches the one on the
monitor.
Phase 2 successfully concludes once every voting representative
confirms that the contents of the TRC payload are correct.
3.2.2.3.3. Phase 3: TRC Signing
In Phase 3, each voting representative attaches a signature created
with each one of their private voting keys to the TRC (payload file).
They do this on their own machine. The purpose of signing a TRC that
contains newly introduced public keys with the corresponding private
keys is to prove the possession of the private keys.
Phase 3 concludes after all voting representatives have cast their
votes.
3.2.2.3.4. Phase 4: TRC Validation
In Phase 4, all voting representatives share the signed TRC with the
ceremony administrator. This happens again over the data exchange
device, which goes from one voter to the next. Each voting
representative copies the TRC payload signed with the voter's private
keys from their own machine onto the data exchange device. The last
voter returns the device to the ceremony administrator, who assembles
the final TRC by aggregating the payload data with the votes
(signatures) cast by the voting representatives.
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The signed TRC is validated by inspecting its contents on the monitor
and verifying the signatures based on the exchanged certificates in
Phase 1. The ceremony administrator then shares the signed TRC with
all participants. Each of them must then inspect it once more, and
verify it based on the certificates exchanged in Phase 1. At this
point, the ceremony is completed. All participants have the signed
TRC, and can use it to distribute the trust anchors for their ISD.
4. Deploying the CP PKI - Specifications
This section provides several specifications regarding the deployment
of the control-plane PKI.
4.1. Deploying a TRC
4.1.1. Base TRC
Base TRCs are trust anchors and thus axiomatically trusted. All ASes
within an ISD must be pre-loaded with the currently valid base-
version TRC of their own ISD. For all specifications regarding the
creation and distribution of initial/base TRCs, see Section 3.2.
4.1.2. TRC Update
All non-base TRCs of an ISD are updates of the ISD's base TRC(s).
The TRC update chain consists of regular and sensitive TRC updates.
The specifications and rules that apply to updating a TRC are
described in Section 3.1.5.
4.1.2.1. TRC Update Discovery
Relying parties MUST have at least one valid TRC available. Relying
parties MUST discover TRC updates within the grace period defined in
the updated TRC. They SHOULD discover TRC updates in a matter of
minutes to hours. Regardless of the employed discovery method, the
following requirement must be satisfied:
*Requirement:*
Any entity sending information that is secured through the CP-PKI (be
it during beaconing or path lookup) MUST be able to provide all the
necessary trust material to verify said information.
As it is always possible to communicate with the sender of a packet
(either via path reversal or one-hop paths), this requirement avoids
circular dependencies between authentication and packet forwarding.
The following mechanisms for discovering TRC updates fulfil the above
requirement.
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* _Beaconing Process_
The TRC version is announced in the beaconing process. Each AS
must announce what it considers to be the latest TRC.
Furthermore, each AS must include the hash value of the TRC
contents to facilitate the discovery of discrepancies. Therefore,
relying parties that are part of the beaconing process discover
TRC updates passively. That is, the beacon service in a core AS
notices TRC updates for remote ISDs that are on the beaconing
path. The beacon service in a non-core AS only notices TRC
updates for the local ISD through the beaconing process. The
creation of a new TRC should trigger the generation of new PCBs,
as the propagation of PCBs will help other ASes rapidly discover
the new TRC.
* _Path Lookup_
In every path segment, all ASes must reference the latest TRC of
their ISD. Therefore, when resolving paths, every relying party
will notice TRC updates, even remote ones.
*Note:* The above mechanism only works when there is an active
communication between the relying party and the ISD in question.
4.2. Signing and Verifying Control-Plane Messages
SCION requires that control-plane messages are signed. The main
purpose of the SCION control-plane PKI is providing a mechanism to
distribute and authenticate public keys that are used to verify
control-plane messages and information. For example, each hop
information in a path segment is signed by the respective AS.
Consequently, all relying parties must be able to verify signatures
with the help of the CP-PKI.
The following sections specify the requirements that apply to the
signing and verification of control-plane messages.
4.2.1. Signing a Control-Plane Message
An AS signs control-plane messages with the private key that
corresponds to the (valid) AS' certificate.
The AS MUST attach the following information as signature metadata.
It is the minimum information a relying party requires to identify
which certificate to use to verify the signed message.
* ISD-AS number: The ISD-AS number of the signing entity. For
specification details, see Section 2.2.1.4.1.
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* Subject key identifier: The identifier of the public key that must
be used to verify the message. For specification details, see
Section 2.2.1.9.2.
Additionally, the signer SHOULD include the following information:
* Serial and base number of the latest TRC: Including this
information allows relying parties to discover TRC updates and
trust resets. For specification details, see Section 3.1.2.2.2.
* Timestamp: For many messages, the time at which it was signed is
useful information to ensure freshness.
4.2.2. Verifying a Control-Plane Message
When the relying party receives a control-plane message they want to
verify, the relying party first needs to identify the certificate
needed to validate the corresponding signature on the message.
AS certificates are bundled together with the corresponding signing
CA certificate into certificate chains. For efficiency, SCION
distributes these certificate chains separately from the signed
messages. A certificate chain is verified against the CP root
certificate. However, the root certificate is *not* bundled in the
chain, but with the TRC. This makes it possible to extend the
validity period of the root certificate, and to update the
corresponding TRC, without having to modify the certificate chain.
Now to verify a control-plane message, the relying party must perform
the following steps:
1. Build a collection of root certificates from the latest TRC of
the relevant ISD (that is, the ISD referenced in the signature
metadata of the message). If the grace period
(Section 3.1.2.2.4) introduced by the latest TRC is still on-
going, the root certificates in the second-to-latest TRC must
also be included. For a description on how to build the correct
collection of certificates, see Section 3.1.4.1.
2. If the signature metadata of the message contains the serial and
base number of the latest TRC, the relying party must check that
they have this latest TRC. If not, the relying party must
request the latest TRC.
3. After constructing the pool of root certificates, the relying
party must select a certificate chain used to verify the message.
The AS certificate included in this certificate chain MUST have
the following properties:
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* The ISD-AS number in the subject of the AS certificate MUST
match the ISD-AS number in the signature metadata. See also
Section 2.2.1.4.1.
* The subject key identifier of the AS certificate MUST match
the subject key identifier in the signature metadata. See
also Section 2.2.1.9.2.
* The AS certificate MUST be valid at verification time.
Normally, this will be the current time. In special cases,
e.g., auditing, the time can be set to the past to check if
the message was verifiable at the given time.
4. After selecting a certificate chain to verify the control-plane
messages, the relying party must verify the certificate chain,
by:
* Executing the regular X.509 verification procedure. For
details, see X.509
(https://handle.itu.int/11.1002/1000/13031).
* Checking that
- all subjects of the certificates in the chain carry the
same ISD number (see also Section 2.2.1.6),
- each certificate is of the correct type (see also
Section 2.1), and
- the CA certificate validity period covers the AS
certificate validity period (see also Section 2.2.1.5).
5. If the verification of the certificate chain was successful, the
relying party can now verify the control-plane messages, with the
root certificates from the certificate chain.
If any cryptographic material is missing in the process, the relying
party queries the originator of the message for the missing material.
If it cannot be resolved, the verification process fails.
*Important:* An implication of the above procedure is that path
segments should be verifiable at time of use. It is not enough to
rely on path segments being verified on insert, since TRC updates
that change the root key can invalidate a certificate chain.
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4.3. Creating a New Control-Plane AS Certificate
The steps required to create a new AS certificate are the following:
1. The AS creates a new key pair and a certificate signing request
(CSR) using that key pair.
2. The AS sends the certificate signing request to the relevant CA
within the ISD.
3. The CA uses its CA key and the CSR to create the new AS
certificate.
4. The CA sends the AS certificate back to the AS.
5. Security Considerations
The entire document is about security considerations. More details
will follow in future versions of this draft.
6. IANA Considerations
The PKI requires a root SCION object identifier (OID), as discussed
in Section 2.2.1.4.1. The SCION open source implementation currently
uses the Anapaya IANA Private Enterprise Number (55324) within the
root SCION object identifier (OID). Future iterations of this draft
will discuss whether this or another PEN should be used and comprise
more detailed IANA considerations.
7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/rfc/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.
7.2. Informative References
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[BARRERA17]
Barrera, D., Chuat, L., Perrig, A., Reischuk, R., and P.
Szalachowski, "The SCION internet architecture",
Communications of the ACM vol. 60, no. 6, pp. 56-65,
DOI 10.1145/3085591, May 2017,
<https://doi.org/10.1145/3085591>.
[CHUAT22] Chuat, L., Legner, M., Basin, D., Hausheer, D., Hitz, S.,
Mueller, P., and A. Perrig, "The Complete Guide to SCION",
ISBN 978-3-031-05287-3, 2022,
<https://doi.org/10.1007/978-3-031-05288-0>.
[I-D.scion-components]
Rustignoli, N. and C. de Kater, "SCION Components
Analysis", 2022, <https://datatracker.ietf.org/doc/draft-
rustignoli-panrg-scion-components/>.
[I-D.scion-overview]
de Kater, C., Rustignoli, N., and A. Perrig, "SCION
Overview", 2022, <https://datatracker.ietf.org/doc/draft-
dekater-panrg-scion-overview/>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/rfc/rfc5280>.
[RFC5480] Turner, S., Brown, D., Yiu, K., Housley, R., and T. Polk,
"Elliptic Curve Cryptography Subject Public Key
Information", RFC 5480, DOI 10.17487/RFC5480, March 2009,
<https://www.rfc-editor.org/rfc/rfc5480>.
[RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
RFC 5652, DOI 10.17487/RFC5652, September 2009,
<https://www.rfc-editor.org/rfc/rfc5652>.
[RFC5758] Dang, Q., Santesson, S., Moriarty, K., Brown, D., and T.
Polk, "Internet X.509 Public Key Infrastructure:
Additional Algorithms and Identifiers for DSA and ECDSA",
RFC 5758, DOI 10.17487/RFC5758, January 2010,
<https://www.rfc-editor.org/rfc/rfc5758>.
[RFC8410] Josefsson, S. and J. Schaad, "Algorithm Identifiers for
Ed25519, Ed448, X25519, and X448 for Use in the Internet
X.509 Public Key Infrastructure", RFC 8410,
DOI 10.17487/RFC8410, August 2018,
<https://www.rfc-editor.org/rfc/rfc8410>.
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Acknowledgments
Many thanks go to Juan A. Garcia-Pardo, Francois Wirz and Jordi
Subira Nieto for reviewing this document. We are also very grateful
to Adrian Perrig, for providing guidance and feedback about each
aspect of SCION. Finally, we are indebted to the Anapaya and ETH
SCION development teams, for their practical knowledge and for the
documentation about the CP PKI.
Authors' Addresses
Corine de Kater
ETH Zuerich
Email: corine.dekatermuehlhaeuser@inf.ethz.ch
Nicola Rustignoli
ETH Zuerich
Email: nicola.rustignoli@inf.ethz.ch
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