Network Working Group T. Bruijnzeels
Internet-Draft NLnet Labs
Intended status: Standards Track C. Martinez
Expires: April 19, 2019 LACNIC
R. Austein
Dragon Research Labs
October 16, 2018
RPKI Signed Object for Trust Anchor Keys
draft-ietf-sidrops-signed-tal-02
Abstract
Trust Anchor Locators (TALs) [I-D.ietf-sidrops-https-tal] are used by
Relying Parties in the RPKI to locate and validate Trust Anchor
certificates used in RPKI validation. This document defines an RPKI
signed object for Trust Anchor Keys (TAK), that can be used by Trust
Anchors to signal their set of current keys and the location(s) of
the accompanying CA certiifcates to Relying Parties, as well as
changes to this set in the form of revoked keys and new keys, in
order to support both planned and unplanned key rolls without
impacting RPKI validation.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 19, 2019.
Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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to this document. Code Components extracted from this document must
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Table of Contents
1. Requirements notation . . . . . . . . . . . . . . . . . . . . 3
2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. TAK Object definition . . . . . . . . . . . . . . . . . . . . 4
3.1. The TAK Object Content Type . . . . . . . . . . . . . . . 5
3.2. The TAK Object eContent . . . . . . . . . . . . . . . . . 5
3.2.1. version . . . . . . . . . . . . . . . . . . . . . . . 5
3.2.2. current . . . . . . . . . . . . . . . . . . . . . . . 5
3.2.3. revoked . . . . . . . . . . . . . . . . . . . . . . . 6
3.3. TAK Object Validation . . . . . . . . . . . . . . . . . . 6
4. Maintaining multiple TA keys . . . . . . . . . . . . . . . . 7
4.1. Prepare a new TA key . . . . . . . . . . . . . . . . . . 7
4.2. Publishing for Multiple TA Keys . . . . . . . . . . . . . 7
5. TAK Object Generation and Publication . . . . . . . . . . . . 8
6. Performing TA Key Rolls . . . . . . . . . . . . . . . . . . . 9
6.1. Opting in to Key Rolls . . . . . . . . . . . . . . . . . 10
6.1.1. Trust Anchor . . . . . . . . . . . . . . . . . . . . 10
6.1.2. Relying Parties . . . . . . . . . . . . . . . . . . . 12
6.2. Pre-stage a New Key . . . . . . . . . . . . . . . . . . . 12
6.2.1. Trust Anchor . . . . . . . . . . . . . . . . . . . . 12
6.2.2. Relying Parties . . . . . . . . . . . . . . . . . . . 14
6.3. Planned Key Revocation . . . . . . . . . . . . . . . . . 14
6.3.1. Trust Anchor . . . . . . . . . . . . . . . . . . . . 14
6.3.2. Relying Parties . . . . . . . . . . . . . . . . . . . 17
6.4. Unplanned revocation . . . . . . . . . . . . . . . . . . 17
6.4.1. Trust Anchor . . . . . . . . . . . . . . . . . . . . 17
7. Deployment Considerations . . . . . . . . . . . . . . . . . . 18
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
8.1. OID . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
8.2. File Extension . . . . . . . . . . . . . . . . . . . . . 19
9. Security Considerations . . . . . . . . . . . . . . . . . . . 19
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 19
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 19
11.1. Normative References . . . . . . . . . . . . . . . . . . 19
11.2. Informative References . . . . . . . . . . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21
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1. Requirements notation
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.
2. Overview
Trust Anchor Locators (TALs) [I-D.ietf-sidrops-https-tal] are used by
Relying Parties in the RPKI to locate and validate Trust Anchor (TA)
certificates used in RPKI validation. However, until now there has
been no formal way of notifying Relying Parties (RP) of updates to a
TAL. Such updates may be needed in particular in case a Trust Anchor
needs to perform a planned, or unplanned, key roll.
This document defines a new RPKI signed object that can be used to
document the current set of keys and the loctaion(s) of the
accompanying CA certificates, as well as any changes to this set.
This allows RPs to be notified automatically of such changes, and
enables Trust Anchors to pre-stage a number of operational keys so
that planned and unplanned key rolls can be performed without risking
the invalidation of the RPKI tree under the TA. We call this object
the Trust Anchor Keys (TAK) object.
When Relying Parties (RPs) are first bootstrapped, they use any
current TAL to discover a key and location(s) of the TA
certificate(s) for a TA. The RP can then retreive and validating the
TA certificate, and subsequently validate the manifest [RFC6486] and
CRL [section 5 of @!RFC6487]. However, before processing any other
objects it will then first validate the TAK object, if present. All
enumarated new keys (and locations) are then added to a new list of
current TA keys for this TA. The RP will then recursively fetch and
validate the TA certificates, manifest, CRL and TAK objects for each
of these keys. As a part of this process the RP will also compile a
list of revoked keys enumarated by any of the validly signed TAK
objects. As the final step the RP will then filter out any revoked
TA keys from its new set. This new set now replaces the previous
set.
If the key used to start this process is still considered current,
then validation continues. But if the key was revoked, then
validation is restarted using one of the remaining keys in the set.
This process allows Trust Anchors to operate a set of N current keys,
where any key can effectively revoke any or all of the other keys to
perform either a planned, or an unplanned, key roll. This also
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allows Trust Anchors to produce long lived TAK objects as forward
pointers to RPs, and retire its old key when doing a key roll.
While the generic process is quite involved, the amount of work
needed to support an envisioned normal key roll is fairly limited.
Under normal circumstances a TA will typically have two current keys,
so that is can perform an emergency roll over in case one of the keys
is lost. This means that the RP will need to validate two TAK
objects. However, typically these files will agree that both keys
are current and validation continues.
When a key roll is executed a TA will remove one old key, and
introduce one new (back-up) key. The RP will remove the old key from
its set, and it will not be queried again, and it will add the new
key and its TA certifcate location(s).
Only in a situation where an RP is very outdated can it be expected
that the RP will have to discover several chained TAK object. But,
since it will remove the outdated TALs in this process, this presents
a one time cost only.
Note that in theory a TA can revoke all of its keys and make itself
obsolete. In practice however, a well operated TA will have measures
in place to prevent this. Furthermore they can protect themselves
against key loss to adversaries through the use of such as the use of
a Hardware Security Module (HSM) to protect keys. Protecting against
this mis-operation would incur complexity and guesswork on the RPs.
Therefore it is believed that it is best to keep the process
straightforward, and offer a solution for the more likely issues of
loss of a key, e.g. because an HSM or card set is broken, and
planned key rolls.
3. TAK Object definition
The TAK object makes use of the template for RPKI digitally signed
objects [RFC6488], which defines a Crytopgraphic Message Syntax (CMS)
[RFC5652] wrapper for the Signed TALs content as well as a generic
validation procedure for RPKI signed objects. Therefore, to complete
the specification of the TAK object (see Section 4 of [RFC6488]),
this document defines:
o The OID defined in Section 3.1 that identifies the signed object
as being a TAK. (This OID appears within the eContentType in the
encapContentInfo object as well as the content-type signed
attribute in the signerInfo object).
o The ASN.1 syntax for the TAK eContent defined in Section 3.2.
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o Additional steps to the validation steps specified in [RFC6488]
required to validate the TAK, defined in Section 3.3.
3.1. The TAK Object Content Type
This document requests an OID for TAK objects as follows:
signed-Tal OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840)
rsadsi(113549) pkcs(1) pkcs9(9) 16 id-smime (1) TBD }
This OID MUST appear both within the eContentType in the
encapContentInfo object as well as the content-type signed attribute
in the signerInfo object (see [RFC6488])
3.2. The TAK Object eContent
The content of a TAK object is ASN.1 encoded using the Distinguished
Encoding Rules (DER) [X.690], and is defined as follows:
TAK ::= SEQUENCE {
version INTEGER DEFAULT 0,
current ::= SEQUENCE SIZE (1..MAX) OF CurrentKey,
revoked ::= SEQUENCE OF SubjectPublicKeyInfo
}
CurrentKey ::= SEQUENCE {
certificateURIs SEQUENCE SIZE (1..MAX) OF CertificateURI,
subjectPublicKeyInfo SubjectPublicKeyInfo
}
CertificateURI ::= IA5String
SubjectPublicKeyInfo ::= SEQUENCE {
algorithm AlgorithmIdentifier,
subjectPublicKey BIT STRING
}
3.2.1. version
The version number of the TAK object MUST be 0.
3.2.2. current
This field defines the set of current keys (CurrentKey) according to
the signer of this Signed TALs object.
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3.2.2.1. CurrentKey
This field defines a current TA Key, equivalent to [I-D.ietf-sidrops-
https-tal]. This structure contains a sequence of one or more URIs
and a SubjectPublicKeyInfo.
3.2.2.1.1. certificateURIs
This field is equivalent to the URI section in section 2.1 of
[I-D.ietf-sidrops-https-tal]. It MUST contain at least one
CertificateURI element. Each CertificateURI element contains the
IA5String representation of either an rsync URI [RFC5781], or an
HTTPS URI [RFC7230].
3.2.2.1.2. subjectPublicKeyInfo
This field contains a SubjectPublicKeyInfo [section 4.1.2.7 or
@!RFC5280] in DER format [X.690].
3.2.3. revoked
This field contains the list of keys, identified by
SubjectPublicKeyInfo, that are no longer to be used according to the
signer of this document.
3.3. TAK Object Validation
To determine whether a TAK object is valid, the RP MUST perform the
following steps in addition to those specified in [RFC6488]:
o The eContentType OID matches the OID described in Section 3.1
o The TAK object appears as the product of a Trust Anchor CA
certificate.
o This Trust Anchor CA has published only one TAK object in its
repository for this key, and this object appears on the Manifest
as the only entry using the ".tak" extension (see [RFC6481]). In
case more than one TAK object is found, all such objects MUST be
considered invalid.
o The EE certificate of this TAK object describes its Internet
Number Resources (INRs) using the "inherit" attribute
o The decoded TAK content conforms to the format defined in
Section 3.2.
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If the above procedure indicates that the manifest is invalid, then
the TAK object MUST be discarded and treated as though no TAK object
were present.
4. Maintaining multiple TA keys
As described in Section 6 a TA will most likely choose to operate two
keys at any one time in order to be prepared for an emergency key
roll. When a TA operates multiple keys, each key MUST use its own CA
repository publication point as described in [RFC6481]. The CRL and
Manifest [RFC6486] for each of these keys will be unique to each key,
but the TA MUST ensure that equivalent CA certificates and RPKI
signed objects are issued under each key. Note that this is similar
to how such certificates and RPKI signed objects are re-issued as
part of a lower level CA key roll, described in section 4 of
[RFC6489].
4.1. Prepare a new TA key
The Trust Anchors MUST generate a new key pair and generate a new TA
Certificate. For the Subject Information Access (see section 4.8.8.1
of [RFC6487]) this MUST use URIs that will be used by the new key to
publish objects. These URIs MUST be uniqe for use by this new key
only. The Internet Number Resources on this new certificate MUST be
equivalent to those found on the current certificate.
The new TA certificate MUST be published under one or more new
Certificate URIs for use by this new key only.
As decribed above, the TA MUST issue and publish equivalent CA
certificates and RPKI signed objects under this new key.
It is RECOMMENDED that the TA now generates a new TAL
[I-D.ietf-sidrops-https-tal] and verifies that the new Trust Anchor
certificate can be retrieved from all locations, and that it
generates the same results when it is used for top-down validation
instead of (any of) the current TA key(s).
Note that the TA MAY choose to make this TAL available to Relying
Parties, in particular to those that do not support TAK objects, and
for inclusion in the distribution of RP software in order to minimise
the overhead in bootstrapping fresh installations.
4.2. Publishing for Multiple TA Keys
If a TA uses a single remote publication server for its keys using
the RPKI publication protocol [RFC8181], then it MUST include all
<publish/> and <withdraw/> PDUs for the products of each of its keys
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in a single query in order to ensure that they will reflect the same
content at all times.
If a TA uses multiple publication servers then it is by definition
inevitable that the content of different keys will be out of sync at
times. In such cases the TA SHOULD ensure that the duration of these
moments are limited to the shortest possible time. Furthermore the
following should be observed:
o It is strongly RECOMMENDED that TAs do not issue any RPKI Signed
Objects, such as ROAs [RFC6482], but limit their operations to
maintaining a CRL, Manifest and CA certificates only. If an
organisation maintaining a TA has an operational need for such
objects then it is strongly RECOMMENDED that they operate a
separate non-TA CA as a child of their TA for these operations.
If this approach is used the remaining issues regarding temporary
inconsistencies between multiple TA key repository publication
points is greatly reduced.
o In cases where a CA certificate is revoked completely, or replaced
by a certifcate with a reduced set of resources, these changes
will not take effect fully until all the TA keys repository
publication points have been updated. Given that TA key
operations are normally performed infrequently we don't expect
that this is a problem. I.e. if the revocation or shrinking of an
issued CA certificate is staged for days, or weeks anyway, then
experiencing a delay of several minutes for the repository
publication points to all be updated is fairly insignificant.
o In cases where a CA certificate is replaced by a certifcate with
an extend set of resources the TA MUST inform the receiving CA
only after all its repository publication points have been
updated. This ensures that the receiveing CA will not issue any
products that could be invalid if an RP uses a TA key just before
the CA certificate was due to be updated.
5. TAK Object Generation and Publication
A TA MAY choose to use TAK objects to communicate its set of current,
and revoked keys. If a TA chooses to use TAK objects, then it SHOULD
generate and publish TAK objects under each of its current keys. An
exception to this rule exists when a TA has lost permanent access to
one of its keys or the accompanying repository publication point. In
such cases however, the key in question MUST be revoked as described
below in Section 6.
A non-normative guideline for naming this object is that the filename
chosen for the Signed TAL Object in the publication repository be a
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value derived from the public key part of the entity's key pair,
using the algorithm described for CRLs in section 2.2 of [RFC6481]
for generation of filenames. The filename extension of ".tak" MUST
be used to denote the object as a TAK. Note that this is in-line
with filename extensions defined in section 7.2 of [RFC6481]
In order to generate the TAK Objects, the TA MUST perform the
following actions:
o The TA MUST generate a key pair for a "one-time-use" EE
certificate to use for the TAK
o The TA MUST generate a one-time-use EE certificate for the TAK
o This EE certificate MUST have an SIA extension access description
field with an accessMethod OID value of id-ad-signedobject, where
the associated accessLocation references the publication point of
the TAK as an object URL.
o As described in [RFC6487], an [RFC3779] extension is required in
the EE certificate used for this object. However, because the
resource set is irrelevant to this object type, this certificate
MUST describe its Internet Number Resources (INRs) using the
"inherit" attribute, rather than explicit description of a
resource set.
o This EE certificate MUST have a "notBefore" time that matches, or
predates the moment that the TAK will be published.
o This EE certificate MUST have a "notAfter" time that reflects the
intended duration for which this TAK will be published. If the EE
certificate for a Signed TAL is expired, it MUST no longer be
published, but it MAY be replaced by a newly generated TAK object
with equivalent content and an updated "notAfter" time.
o The same set of current keys (see Section 3.2.2) MUST be included
on each TAK object for each current key.
o The TAK object MUST include all revoked keys (see Section 3.2.3)
that became revoked while the key signing the TAK in question was
current.
6. Performing TA Key Rolls
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6.1. Opting in to Key Rolls
6.1.1. Trust Anchor
For simplicitly let's start with a situation where a TA has only one
key. The TA wants to start using TAK objects to perform key rolls in
future, so it introduces a TAK object under its single key 'A'. The
repository structure looks as follows (irrelevant details omitted):
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+--------------------+
| A.MFT |
+--------------------+
| A.CRL <hash> |
| A.TAK <hash> |
| C1-A.CER <hash> |
| C2-A.CER <hash> |
+--------------------+
+--------------------+
| A.CRL |
+--------------------+
| revocations.. |
+--------------------+
+--------------------+
| A.TAK |
+--------------------+
| current: A |
| revoked: none |
+--------------------+
+--------------------+
| C1-A.CER |
+--------------------+
| resources: C1 res |
| subject: C1 name |
| pub key: C1 key |
| SIA: C1 SIAs |
| AKI: A |
+--------------------+
+--------------------+
| C2-A.CER |
+--------------------+
| resources: C2 res |
| subject: C2 name |
| pub key: C2 key |
| SIA: C2 SIAs |
| AKI: A |
+--------------------+
So, the TA publishes a CRL and MFT under its key A, listing a TAK
object and in this case two certificates issued to children 'C1' and
'C2' signed using key A. The TAK object lists key 'A' as the only
current key, and has no revoked keys.
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6.1.2. Relying Parties
Relying Parties who have a TAL for key 'A' configured will discover
the TAK object. If the RP does not support this object, it will
reject this object but continue to validate the remaining RPKI tree
as usual. If the RP does support TAK objects it will conclude that
key 'A' is the one and only current key, and will proceed to validate
the remaining RPKI tree as usual.
6.2. Pre-stage a New Key
6.2.1. Trust Anchor
Now the TA prestages a new key 'B' and produces equivalent CA
certificates for children 'C1' and 'C2', i.e. the resources, subject
name, public key and SIA etc are all equivalent, but these
certificates are signed under key 'B'. (See Section 4 for a more
thorough description of this). The TAK object for key 'B' recognises
both keys 'A' and 'B' as current.
The repostory structure and TAK object for key B are then as follows:
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+--------------------+
| B.MFT |
+--------------------+
| B.CRL <hash> |
| B.TAK <hash> |
| C1-B.CER <hash> |
| C2-B.CER <hash> |
+--------------------+
+--------------------+
| B.CRL |
+--------------------+
| revocations.. |
+--------------------+
+--------------------+
| B.TAK |
+--------------------+
| current: A, B |
| revoked: none |
+--------------------+
+--------------------+
| C1-B.CER |
+--------------------+
| resources: C1 res |
| subject: C1 name |
| pub key: C1 key |
| SIA: C1 SIAs |
| AKI: B |
+--------------------+
+--------------------+
| C2-B.CER |
+--------------------+
| resources: C2 res |
| subject: C2 name |
| pub key: C2 key |
| SIA: C2 SIAs |
| AKI: B |
+--------------------+
When the TA is certain that the content for key 'B' is correct, it
can also update the TAK object for key 'A' to include 'B':
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+--------------------+
| A.TAK |
+--------------------+
| current: A, B |
| revoked: none |
+--------------------+
One way to do this is by generating a TAL
[I-D.ietf-sidrops-https-tal] for key B and verifying that validation
using this yields the same results as validation using the TAL for
key A would. However, note, that it is preferred that this is done
as part of an automated process that is sufficiently well tested, and
that the contents of the repositories for keys 'A' and 'B' are
updated as a single delta if the publication protocol [RFC8181] is
used (see also: Section 5).
6.2.2. Relying Parties
Relying Parties who have a TAL for key 'A' configured will discover
the TAK object. If the RP does not support this object, it will
reject this object but continue to validate the remaining RPKI tree
as usual. If the RP does support TAK objects it will conclude that
there are now two keys 'A' and 'B', and no revoked keys that it
should be aware of. Since key 'A' is still current, the RP will
continue to validate the RPKI tree structure using the repository for
key 'A', ignoring the non-TAK objects in the repository for key 'B'.
The result will be the same for Relying Parties who have a TAL for
key 'B' configured, because both keys are equivalent at this time.
6.3. Planned Key Revocation
6.3.1. Trust Anchor
The TA has now decided that key 'A' must be revoked. It still has
access to this key and the repository, so it can perform a planned
key roll. In addition to revoking key 'A', the TA will also generate
new key 'C' to ensure that it has at least two current keys at all
times for redundancy.
Keys 'B' and 'C' will become current keys on the TAK objects for all
keys: 'A', 'B' and 'C'. Key 'A' will become part of the revoked keys
on the TAK objects for keys 'A' and 'B'. Note that it is not needed
to list key 'A' as revoked on the TAK file for key 'C', because RPs
will only learn about key 'C' at the same time as learning about the
revocation of key 'A' (see also below).
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The TA will publish a long-lived TAK file and MFT and CRL only for
key 'A' and publish these objects as waypointers for RPs that have a
TAL pointing at key 'A' before destroying key 'A'.
The resulting structure for key 'A' will be as follows:
+--------------------+
| A.MFT |
+--------------------+
| A.CRL <hash> |
| A.TAK <hash> |
+--------------------+
+--------------------+
| A.CRL |
+--------------------+
| revocations.. |
+--------------------+
+--------------------+
| A.TAK |
+--------------------+
| current: B, C |
| revoked: A |
+--------------------+
The resulting structures for keys 'B' and 'C' will be as follows:
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+--------------------+ +--------------------+
| B.MFT | | C.MFT |
+--------------------+ +--------------------+
| B.CRL <hash> | | B.CRL <hash> |
| B.TAK <hash> | | B.TAK <hash> |
| C1-B.CER <hash> | | C1-C.CER <hash> |
| C2-B.CER <hash> | | C2-C.CER <hash> |
+--------------------+ +--------------------+
+--------------------+ +--------------------+
| B.CRL | | C.CRL |
+--------------------+ +--------------------+
| revocations.. | | revocations.. |
+--------------------+ +--------------------+
+--------------------+ +--------------------+
| B.TAK | | C.TAK |
+--------------------+ +--------------------+
| current: B, C | | current: B, C |
| revoked: A | | revoked: <none> |
+--------------------+ +--------------------+
+--------------------+ +--------------------+
| C1-B.CER | | C1-C.CER |
+--------------------+ +--------------------+
| resources: C1 res | | resources: C1 res |
| subject: C1 name | | subject: C1 name |
| pub key: C1 key | | pub key: C1 key |
| SIA: C1 SIAs | | SIA: C1 SIAs |
| AKI: B | | AKI: C |
+--------------------+ +--------------------+
+--------------------+ +--------------------+
| C2-B.CER | | C2-B.CER |
+--------------------+ +--------------------+
| resources: C2 res | | resources: C2 res |
| subject: C2 name | | subject: C2 name |
| pub key: C2 key | | pub key: C2 key |
| SIA: C2 SIAs | | SIA: C2 SIAs |
| AKI: B | | AKI: B |
+--------------------+ +--------------------+
In addition to this the TA SHOULD reach out to RP vendors so that
they can update the TAL included in the RP software distribution to
use key 'B'.
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6.3.2. Relying Parties
Relying Parties who have a TAL for key 'A' configured will discover
the TAK object. If the RP does not support this object, it will
reject this object but continue to validate the remaining RPKI tree
as usual. In this case that means that validation will stop, because
there are no more objects under key 'A'. Therefore it is important
that RPs that do not support TAK files are updated to use the TAL for
key 'B' through some other process.
If the RP uses a TAL for key 'A' and it supports TAK objects, it will
discover that the TAL for key 'A' has keys 'B' and 'C' as current,
and revokes itself. It will then proceed to process keys 'B' and 'C'
and find TALs which list the same current keys. So, it will now
replace its notion of the current key set for this TA based on its
TAL (key 'A') with what it learned. To keep things simple the RP
will now conclude that it should re-start validation using a
remaining current key, in this case key either 'B' or 'C' may be
used.
If the RP already had a TAL for key 'B' and it supports TAK objects,
or it simply started with key 'B' because it added it to its set of
current keys when this key was pre-staged (see Section 6.2), it will
learn that key 'A' is revoked and therefore will not attempt to
verify the TAK file for key 'A'. It will also learn about key 'C'
and inspect this key's TAL, and discover that only keys 'B' and 'C'
are considered current. Since it started the validation process with
a key that is still current, it can proceed to validate the RPKI tree
using the repository under key 'B'.
6.4. Unplanned revocation
6.4.1. Trust Anchor
Now keys 'B' and 'C' are current. The TA may have intended to revoke
key 'B', essentially rolling over to key 'C' and a new key 'D', but
let us suppose that the TA lost access to key 'C'. In this case the
TA will simply revoke key 'C' instead, and still introduce a new key
'D'.
The major difference with the process described above for planned
rolls, is that now the TA will not be able to update the TAK object,
MFT or CRL for key 'C'. However, because all TAL objects for current
keys are evaluated before tree validation is performed, it is safe to
leave these objects in a repository. Keys 'B' and 'D' will simply
mark key 'C' as being revoked.
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If an RP still has a TAL pointing at key 'C' it will discover that
key 'D' is added, and that key 'B' has been revoked through the TAK
object published for keys 'B' and 'D'. At least, as long as the the
MFT and TAK EE certificates have not expired, and the CRL and MFT are
not stale.
If the TA is absolutely sure that the TAL for key 'C' never shipped
with any RP distribution, then it would also be safe to delete the
repository key 'C' altogether. RPs will learn that 'C' is revoked,
and therefore will not even attempt to download the TAK object.
However, it is hard to be certain of this and there this is NOT
RECOMMENDED.
7. Deployment Considerations
Including Signed TAL objects while RP tools do not support this
standard will result in these RPs rejecting these objects. It is not
expected that this will result in the invalidation of any other
object under a Trust Anchor.
That said, the flagging mechanism introduced here can only be relied
on once a majority of RPs support it. Defining when that moment
arrives is by definition something that cannot be established at the
time of writing this document. Until such time, TAs SHOULD continue
to generate unsigned TAL files [I-D.ietf-sidrops-https-tal], and
indicate which should be considered their current TAL, and
communicate them to RPs through other means.
However, once a majority of RPs support this mechanism it would be
RECOMMENDED that Trust Anchor operators perform key rolls regularly.
The most assured way to know that such key rolls will work is by
making them a part of normal operations. Determining when this
moment arrives is by definition out of scope for this document, as it
should be based on operational experience.
8. IANA Considerations
8.1. OID
IANA is to add the following to the "RPKI Signed Objects" registry:
Decimal | Description | References
--------+--------------------------------+---------------
TBD | Trust Anchor Keys | [section 3.1]
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8.2. File Extension
IANA is to add an item for the Signed TAL file extension to the "RPKI
Repository Name Scheme" created by [RFC6481] as follows:
Extension | RPKI Object | References
-----------+-------------------------------------------
.tak | Trust Anchor Keys | [this document]
9. Security Considerations
TBD
10. Acknowledgements
The authors wish to thank Martin Hoffmann for a thourough review of
this document.
11. References
11.1. Normative References
[I-D.ietf-sidrops-https-tal]
Huston, G., Weiler, S., Michaelson, G., Kent, S., and T.
Bruijnzeels, "Resource Public Key Infrastructure (RPKI)
Trust Anchor Locator", draft-ietf-sidrops-https-tal-05
(work in progress), October 2018.
[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/info/rfc2119>.
[RFC3779] Lynn, C., Kent, S., and K. Seo, "X.509 Extensions for IP
Addresses and AS Identifiers", RFC 3779,
DOI 10.17487/RFC3779, June 2004,
<https://www.rfc-editor.org/info/rfc3779>.
[RFC5781] Weiler, S., Ward, D., and R. Housley, "The rsync URI
Scheme", RFC 5781, DOI 10.17487/RFC5781, February 2010,
<https://www.rfc-editor.org/info/rfc5781>.
[RFC6481] Huston, G., Loomans, R., and G. Michaelson, "A Profile for
Resource Certificate Repository Structure", RFC 6481,
DOI 10.17487/RFC6481, February 2012,
<https://www.rfc-editor.org/info/rfc6481>.
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[RFC6482] Lepinski, M., Kent, S., and D. Kong, "A Profile for Route
Origin Authorizations (ROAs)", RFC 6482,
DOI 10.17487/RFC6482, February 2012,
<https://www.rfc-editor.org/info/rfc6482>.
[RFC6486] Austein, R., Huston, G., Kent, S., and M. Lepinski,
"Manifests for the Resource Public Key Infrastructure
(RPKI)", RFC 6486, DOI 10.17487/RFC6486, February 2012,
<https://www.rfc-editor.org/info/rfc6486>.
[RFC6487] Huston, G., Michaelson, G., and R. Loomans, "A Profile for
X.509 PKIX Resource Certificates", RFC 6487,
DOI 10.17487/RFC6487, February 2012,
<https://www.rfc-editor.org/info/rfc6487>.
[RFC6488] Lepinski, M., Chi, A., and S. Kent, "Signed Object
Template for the Resource Public Key Infrastructure
(RPKI)", RFC 6488, DOI 10.17487/RFC6488, February 2012,
<https://www.rfc-editor.org/info/rfc6488>.
[RFC6489] Huston, G., Michaelson, G., and S. Kent, "Certification
Authority (CA) Key Rollover in the Resource Public Key
Infrastructure (RPKI)", BCP 174, RFC 6489,
DOI 10.17487/RFC6489, February 2012,
<https://www.rfc-editor.org/info/rfc6489>.
[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing",
RFC 7230, DOI 10.17487/RFC7230, June 2014,
<https://www.rfc-editor.org/info/rfc7230>.
[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/info/rfc8174>.
[RFC8181] Weiler, S., Sonalker, A., and R. Austein, "A Publication
Protocol for the Resource Public Key Infrastructure
(RPKI)", RFC 8181, DOI 10.17487/RFC8181, July 2017,
<https://www.rfc-editor.org/info/rfc8181>.
[X.690] ITU-T Recommendation X.690 (2002) | ISO/IEC 8825-1:2002,
"Information technology - ASN.1 encoding rules:
Specification of Basic Encoding Rules (BER), Canonical
Encoding Rules (CER) and Distinguished Encoding Rules
(DER)", 2002.
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11.2. Informative References
[RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
RFC 5652, DOI 10.17487/RFC5652, September 2009,
<https://www.rfc-editor.org/info/rfc5652>.
Authors' Addresses
Tim Bruijnzeels
NLnet Labs
Email: tim@nlnetlabs.nl
URI: https://www.nlnetlabs.nl/
Carlos Martinez
LACNIC
Email: carlos@lacnic.net
URI: https://www.lacnic.net/
Rob Austein
Dragon Research Labs
Email: sra@hactrn.net
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