Delegated Credentials for TLS
draft-ietf-tls-subcerts-10
Network Working Group R. Barnes
Internet-Draft Cisco
Intended status: Standards Track S. Iyengar
Expires: 28 July 2021 Facebook
N. Sullivan
Cloudflare
E. Rescorla
Mozilla
24 January 2021
Delegated Credentials for TLS
draft-ietf-tls-subcerts-10
Abstract
The organizational separation between the operator of a TLS endpoint
and the certification authority can create limitations. For example,
the lifetime of certificates, how they may be used, and the
algorithms they support are ultimately determined by the
certification authority. This document describes a mechanism by
which operators may delegate their own credentials for use in TLS,
without breaking compatibility with peers that do not support this
specification.
Discussion Venues
This note is to be removed before publishing as an RFC.
Source for this draft and an issue tracker can be found at
https://github.com/tlswg/tls-subcerts (https://github.com/tlswg/tls-
subcerts).
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
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
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This Internet-Draft will expire on 28 July 2021.
Copyright Notice
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions and Terminology . . . . . . . . . . . . . . . . . 3
2.1. Change Log . . . . . . . . . . . . . . . . . . . . . . . 4
3. Solution Overview . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Rationale . . . . . . . . . . . . . . . . . . . . . . . . 6
3.2. Related Work . . . . . . . . . . . . . . . . . . . . . . 7
4. Delegated Credentials . . . . . . . . . . . . . . . . . . . . 8
4.1. Client and Server Behavior . . . . . . . . . . . . . . . 10
4.1.1. Server Authentication . . . . . . . . . . . . . . . . 10
4.1.2. Client Authentication . . . . . . . . . . . . . . . . 10
4.1.3. Validating a Delegated Credential . . . . . . . . . . 11
4.2. Certificate Requirements . . . . . . . . . . . . . . . . 12
5. Operational Considerations . . . . . . . . . . . . . . . . . 12
5.1. Client Clock Skew . . . . . . . . . . . . . . . . . . . . 13
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
7. Security Considerations . . . . . . . . . . . . . . . . . . . 13
7.1. Security of Delegated Credential's Private Key . . . . . 13
7.2. Re-use of Delegated Credentials in Multiple
Contexts . . . . . . . . . . . . . . . . . . . . . . . . 14
7.3. Revocation of Delegated Credentials . . . . . . . . . . . 14
7.4. Interactions with Session Resumption . . . . . . . . . . 14
7.5. Privacy Considerations . . . . . . . . . . . . . . . . . 14
7.6. The Impact of Signature Forgery Attacks . . . . . . . . . 14
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 15
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 15
9.1. Normative References . . . . . . . . . . . . . . . . . . 15
9.2. Informative References . . . . . . . . . . . . . . . . . 16
Appendix A. ASN.1 Module . . . . . . . . . . . . . . . . . . . . 17
Appendix B. Example Certificate . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18
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1. Introduction
Typically, a TLS server uses a certificate provided by some entity
other than the operator of the server (a "Certification Authority" or
CA) [RFC8446] [RFC5280]. This organizational separation makes the
TLS server operator dependent on the CA for some aspects of its
operations, for example:
* Whenever the server operator wants to deploy a new certificate, it
has to interact with the CA.
* The server operator can only use TLS signature schemes for which
the CA will issue credentials.
These dependencies cause problems in practice. Server operators
often deploy TLS termination services in locations such as remote
data centers or Content Delivery Networks (CDNs) where it may be
difficult to detect key compromises. Short-lived certificates may be
used to limit the exposure of keys in these cases.
However, short-lived certificates need to be renewed more frequently
than long-lived certificates. If an external CA is unable to issue a
certificate in time to replace a deployed certificate, the server
would no longer be able to present a valid certificate to clients.
With short-lived certificates, there is a smaller window of time to
renew a certificates and therefore a higher risk that an outage at a
CA will negatively affect the uptime of the service.
To reduce the dependency on external CAs, this document proposes a
limited delegation mechanism that allows a TLS peer to issue its own
credentials within the scope of a certificate issued by an external
CA. These credentials only enable the recipient of the delegation to
speak for names that the CA has authorized. Furthermore, this
mechanism allows the server to use modern signature algorithms such
as Ed25519 [RFC8032] even if their CA does not support them.
We will refer to the certificate issued by the CA as a "certificate",
or "delegation certificate", and the one issued by the operator as a
"delegated credential" or "DC".
2. Conventions and Terminology
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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2.1. Change Log
RFC EDITOR PLEASE DELETE THIS SECTION.
(*) indicates changes to the wire protocol.
draft-10 * Address superficial comments * Add example certificate
draft-09
* Address case nits
* Fix section bullets in 4.1.3.
* Add operational considerations section for clock skew
* Add text around using an oracle to forge DCs in the future and
past
* Add text about certificate extension vs EKU
draft-08
* Include details about the impact of signature forgery attacks
* Copy edits
* Fix section about DC reuse
* Incorporate feedback from Jonathan Hammell and Kevin Jacobs on the
list
draft-07
* Minor text improvements
draft-06
* Modified IANA section, fixed nits
draft-05
* Removed support for PKCS 1.5 RSA signature algorithms.
* Additional security considerations.
draft-04
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* Add support for client certificates.
draft-03
* Remove protocol version from the Credential structure. (*)
draft-02
* Change public key type. (*)
* Change DelegationUsage extension to be NULL and define its object
identifier.
* Drop support for TLS 1.2.
* Add the protocol version and credential signature algorithm to the
Credential structure. (*)
* Specify undefined behavior in a few cases: when the client
receives a DC without indicated support; when the client indicates
the extension in an invalid protocol version; and when DCs are
sent as extensions to certificates other than the end-entity
certificate.
3. Solution Overview
A delegated credential (DC) is a digitally signed data structure with
two semantic fields: a validity interval and a public key (along with
its associated signature algorithm). The signature on the delegated
credential indicates a delegation from the certificate that is issued
to the peer. The private key used to sign a credential corresponds
to the public key of the peer's X.509 end-entity certificate
[RFC5280].
A TLS handshake that uses delegated credentials differs from a
standard handshake in a few important ways:
* The initiating peer provides an extension in its ClientHello or
CertificateRequest that indicates support for this mechanism.
* The peer sending the Certificate message provides both the
certificate chain terminating in its certificate as well as the
delegated credential.
* The authenticating initiator uses information from the peer's
certificate to verify the delegated credential and that the peer
is asserting an expected identity.
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* Peers accepting the delegated credential use it as the certificate
key for the TLS handshake
As detailed in Section 4, the delegated credential is
cryptographically bound to the end-entity certificate with which the
credential may be used. This document specifies the use of delegated
credentials in TLS 1.3 or later; their use in prior versions of the
protocol is not allowed.
Delegated credentials allow a peer to terminate TLS connections on
behalf of the certificate owner. If a credential is stolen, there is
no mechanism for revoking it without revoking the certificate itself.
To limit exposure in case of the compromise of a delegated
credential's private key, delegated credentials have a maximum
validity period. In the absence of an application profile standard
specifying otherwise, the maximum validity period is set to 7 days.
Peers MUST NOT issue credentials with a validity period longer than
the maximum validity period. This mechanism is described in detail
in Section 4.1.
It was noted in [XPROT] that certificates in use by servers that
support outdated protocols such as SSLv2 can be used to forge
signatures for certificates that contain the keyEncipherment KeyUsage
([RFC5280] section 4.2.1.3). In order to prevent this type of cross-
protocol attack, we define a new DelegationUsage extension to X.509
that permits use of delegated credentials. (See Section 4.2.)
3.1. Rationale
Delegated credentials present a better alternative than other
delegation mechanisms like proxy certificates [RFC3820] for several
reasons:
* There is no change needed to certificate validation at the PKI
layer.
* X.509 semantics are very rich. This can cause unintended
consequences if a service owner creates a proxy certificate where
the properties differ from the leaf certificate. For this reason,
delegated credentials have very restricted semantics that should
not conflict with X.509 semantics.
* Proxy certificates rely on the certificate path building process
to establish a binding between the proxy certificate and the
server certificate. Since the certificate path building process
is not cryptographically protected, it is possible that a proxy
certificate could be bound to another certificate with the same
public key, with different X.509 parameters. Delegated
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credentials, which rely on a cryptographic binding between the
entire certificate and the delegated credential, cannot.
* Each delegated credential is bound to a specific signature
algorithm for use use in the TLS handshake ([RFC8446] section
4.2.3). This prevents them from being used with other, perhaps
unintended signature algorithms.
3.2. Related Work
Many of the use cases for delegated credentials can also be addressed
using purely server-side mechanisms that do not require changes to
client behavior (e.g., a PKCS#11 interface or a remote signing
mechanism [KEYLESS]). These mechanisms, however, incur per-
transaction latency, since the front-end server has to interact with
a back-end server that holds a private key. The mechanism proposed
in this document allows the delegation to be done off-line, with no
per-transaction latency. The figure below compares the message flows
for these two mechanisms with TLS 1.3 [RFC8446].
Remote key signing:
Client Front-End Back-End
|----ClientHello--->| |
|<---ServerHello----| |
|<---Certificate----| |
| |<---remote sign---->|
|<---CertVerify-----| |
| ... | |
Delegated Credential:
Client Front-End Back-End
| |<--DC distribution->|
|----ClientHello--->| |
|<---ServerHello----| |
|<---Certificate----| |
|<---CertVerify-----| |
| ... | |
These two mechanisms can be complementary. A server could use
delegated credentials for clients that support them, while using
[KEYLESS] to support legacy clients. The private key for a delegated
credential can be used in place of a certificate private key, so it
is important that the Front-End and Back-End are parties with a
trusted relationship.
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Use of short-lived certificates with automated certificate issuance,
e.g., with Automated Certificate Management Environment (ACME)
[RFC8555], reduces the risk of key compromise, but has several
limitations. Specifically, it introduces an operationally-critical
dependency on an external party (the CA). It also limits the types
of algorithms supported for TLS authentication to those the CA is
willing to issue a certificate for. Nonetheless, existing automated
issuance APIs like ACME may be useful for provisioning delegated
credentials.
4. Delegated Credentials
While X.509 forbids end-entity certificates from being used as
issuers for other certificates, it is valid to use them to issue
other signed objects as long as the certificate contains the
digitalSignature KeyUsage ([RFC5280] section 4.2.1.3). We define a
new signed object format that would encode only the semantics that
are needed for this application. The Credential has the following
structure:
struct {
uint32 valid_time;
SignatureScheme expected_cert_verify_algorithm;
opaque ASN1_subjectPublicKeyInfo<1..2^24-1>;
} Credential;
valid_time: Time in seconds relative to the beginning of the
delegation certificate's notBefore value after which the delegated
credential is no longer valid. Endpoints will reject delegate
credentials with valid_times exceeding 7 days (as described in
Section 4.1).
expected_cert_verify_algorithm: The signature algorithm of the
Credential key pair, where the type SignatureScheme is as defined
in [RFC8446]. This is expected to be the same as the sender's
CertificateVerify.algorithm. Only signature algorithms allowed
for use in CertificateVerify messages are allowed. When using
RSA, the public key MUST NOT use the rsaEncryption OID. As a
result, the following algorithms are not allowed for use with
delegated credentials: rsa_pss_rsae_sha256, rsa_pss_rsae_sha384,
rsa_pss_rsae_sha512.
ASN1_subjectPublicKeyInfo: The Credential's public key, a DER-
encoded [X.690] SubjectPublicKeyInfo as defined in [RFC5280].
The DelegatedCredential has the following structure:
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struct {
Credential cred;
SignatureScheme algorithm;
opaque signature<0..2^16-1>;
} DelegatedCredential;
cred: The Credential structure as previously defined.
algorithm: The signature algorithm used to verify
DelegatedCredential.signature.
signature: The delegation, a signature that binds the credential to
the end-entity certificate's public key as specified below. The
signature scheme is specified by DelegatedCredential.algorithm.
The signature of the DelegatedCredential is computed over the
concatenation of:
1. A string that consists of octet 32 (0x20) repeated 64 times.
2. The context string "TLS, server delegated credentials" for server
authentication and "TLS, client delegated credentials" for client
authentication.
3. A single 0 byte, which serves as the separator.
4. The DER-encoded X.509 end-entity certificate used to sign the
DelegatedCredential.
5. DelegatedCredential.cred.
6. DelegatedCredential.algorithm.
The signature is computed by using the private key of the peer's end-
entity certificate, with the algorithm indicated by
DelegatedCredential.algorithm.
The signature effectively binds the credential to the parameters of
the handshake in which it is used. In particular, it ensures that
credentials are only used with the certificate and signature
algorithm chosen by the delegator.
The code changes required in order to create and verify delegated
credentials, and the implementation complexity this entails, are
localized to the TLS stack. This has the advantage of avoiding
changes to security-critical and often delicate PKI code.
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4.1. Client and Server Behavior
This document defines the following TLS extension code point.
enum {
...
delegated_credential(34),
(65535)
} ExtensionType;
4.1.1. Server Authentication
A client which supports this specification SHALL send a
"delegated_credential" extension in its ClientHello. The body of the
extension consists of a SignatureSchemeList (defined in [RFC8446]):
struct {
SignatureScheme supported_signature_algorithm<2..2^16-2>;
} SignatureSchemeList;
If the client receives a delegated credential without indicating
support, then the client MUST abort with an "unexpected_message"
alert.
If the extension is present, the server MAY send a delegated
credential; if the extension is not present, the server MUST NOT send
a delegated credential. The server MUST ignore the extension unless
TLS 1.3 or a later version is negotiated.
The server MUST send the delegated credential as an extension in the
CertificateEntry of its end-entity certificate; the client SHOULD
ignore delegated credentials sent as extensions to any other
certificate.
The expected_cert_verify_algorithm field MUST be of a type advertised
by the client in the SignatureSchemeList and is considered invalid
otherwise. Clients that receive invalid delegated credentials MUST
terminate the connection with an "illegal_parameter" alert.
4.1.2. Client Authentication
A server that supports this specification SHALL send a
"delegated_credential" extension in the CertificateRequest message
when requesting client authentication. The body of the extension
consists of a SignatureSchemeList. If the server receives a
delegated credential without indicating support in its
CertificateRequest, then the server MUST abort with an
"unexpected_message" alert.
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If the extension is present, the client MAY send a delegated
credential; if the extension is not present, the client MUST NOT send
a delegated credential. The client MUST ignore the extension unless
TLS 1.3 or a later version is negotiated.
The client MUST send the delegated credential as an extension in the
CertificateEntry of its end-entity certificate; the server SHOULD
ignore delegated credentials sent as extensions to any other
certificate.
The algorithm field MUST be of a type advertised by the server in the
"signature_algorithms" extension of the CertificateRequest message
and the expected_cert_verify_algorithm field MUST be of a type
advertised by the server in the SignatureSchemeList and considered
invalid otherwise. Servers that receive invalid delegated
credentials MUST terminate the connection with an "illegal_parameter"
alert.
4.1.3. Validating a Delegated Credential
On receiving a delegated credential and a certificate chain, the peer
validates the certificate chain and matches the end-entity
certificate to the peer's expected identity. It also takes the
following steps:
1. Validate that DelegatedCredential.cred.valid_time is no more than
7 days.
2. Verify that the current time is within the validity interval of
the credential. This is done by asserting that the current time
is no more than the delegation certificate's notBefore value plus
DelegatedCredential.cred.valid_time.
3. Verify that the delegated credential's remaining validity time is
no more than the maximum validity period. This is done by
asserting that the current time is no more than the delegation
certificate's notBefore value plus
DelegatedCredential.cred.valid_time plus the maximum validity
period.
4. Verify that expected_cert_verify_algorithm matches the scheme
indicated in the peer's CertificateVerify message and that the
algorithm is allowed for use with delegated credentials.
5. Verify that the end-entity certificate satisfies the conditions
in Section 4.2.
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6. Use the public key in the peer's end-entity certificate to verify
the signature of the credential using the algorithm indicated by
DelegatedCredential.algorithm.
If one or more of these checks fail, then the delegated credential is
deemed invalid. Clients and servers that receive invalid delegated
credentials MUST terminate the connection with an "illegal_parameter"
alert.
If successful, the participant receiving the Certificate message uses
the public key in DelegatedCredential.cred to verify the signature in
the peer's CertificateVerify message.
4.2. Certificate Requirements
We define a new X.509 extension, DelegationUsage, to be used in the
certificate when the certificate permits the usage of delegated
credentials. What follows is the ASN.1 [X.680] for the
DelegationUsage certificate extension.
ext-delegationUsage EXTENSION ::= {
SYNTAX DelegationUsage IDENTIFIED BY id-pe-delegationUsage
}
DelegationUsage ::= NULL
id-pe-delegationUsage OBJECT IDENTIFIER ::=
{ iso(1) identified-organization(3) dod(6) internet(1)
private(4) enterprise(1) id-cloudflare(44363) 44 }
The extension MUST be marked non-critical. (See Section 4.2 of
[RFC5280].) The client MUST NOT accept a delegated credential unless
the server's end-entity certificate satisfies the following criteria:
* It has the DelegationUsage extension.
* It has the digitalSignature KeyUsage (see the KeyUsage extension
defined in [RFC5280]).
A new extension was chosen instead of adding a new Extended Key Usage
(EKU) to be compatible with deployed TLS and PKI software stacks
without requiring CAs to issue new intermediate certificates.
5. Operational Considerations
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5.1. Client Clock Skew
One of the risks of deploying a short-lived credential system based
on absolute time is client clock skew. If a client's clock is
sufficiently ahead or behind of the server's clock, then clients will
reject delegated credentials that are valid from the server's
perspective. Clock skew also affects the validity of the original
certificates. The lifetime of the delegated credential should be set
taking clock skew into account. Clock skew may affect a delegated
credential at the beginning and end of its validity periods, which
should also be taken into account.
6. IANA Considerations
This document registers the "delegated_credentials" extension in the
"TLS ExtensionType Values" registry. The "delegated_credentials"
extension has been assigned a code point of 34. The IANA registry
lists this extension as "Recommended" (i.e., "Y") and indicates that
it may appear in the ClientHello (CH), CertificateRequest (CR), or
Certificate (CT) messages in TLS 1.3 [RFC8446].
This document also defines an ASN.1 module for the DelegationUsage
certificate extension in Appendix A. IANA has registered value 95
for "id-mod-delegated-credential-extn" in the "SMI Security for PKIX
Module Identifier" (1.3.5.1.5.5.7.0) registry. An OID for the
DelegationUsage certificate extension is not needed as it is already
assigned to the extension from Cloudflare's IANA Private Enterprise
Number (PEN) arc.
7. Security Considerations
7.1. Security of Delegated Credential's Private Key
Delegated credentials limit the exposure of the private key used in a
TLS connection by limiting its validity period. An attacker who
compromises the private key of a delegated credential can act as a
man-in-the-middle until the delegated credential expires. However,
they cannot create new delegated credentials. Thus, delegated
credentials should not be used to send a delegation to an untrusted
party, but is meant to be used between parties that have some trust
relationship with each other. The secrecy of the delegated
credential's private key is thus important and access control
mechanisms SHOULD be used to protect it, including file system
controls, physical security, or hardware security modules.
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7.2. Re-use of Delegated Credentials in Multiple Contexts
It is not possible to use the same delegated credential for both
client and server authentication because issuing parties compute the
corresponding signature using a context string unique to the intended
role (client or server).
7.3. Revocation of Delegated Credentials
Delegated credentials do not provide any additional form of early
revocation. Since it is short lived, the expiry of the delegated
credential revokes the credential. Revocation of the long term
private key that signs the delegated credential (from the end-entity
certificate) also implicitly revokes the delegated credential.
7.4. Interactions with Session Resumption
If a client decides to cache the certificate chain and re-validate it
when resuming a connection, the client SHOULD also cache the
associated delegated credential and re-validate it.
7.5. Privacy Considerations
Delegated credentials can be valid for 7 days and it is much easier
for a service to create delegated credentials than a certificate
signed by a CA. A service could determine the client time and clock
skew by creating several delegated credentials with different expiry
timestamps and observing whether the client would accept it. Client
time could be unique and thus privacy sensitive clients, such as
browsers in incognito mode, who do not trust the service might not
want to advertise support for delegated credentials or limit the
number of probes that a server can perform.
7.6. The Impact of Signature Forgery Attacks
When TLS 1.2 servers support RSA key exchange, they may be vulnerable
to attacks that allow forging an RSA signature over an arbitrary
message [BLEI]. TLS 1.2 [RFC5246] (Section 7.4.7.1.) describes a
mitigation strategy requiring careful implementation of timing
resistant countermeasures for preventing these attacks. Experience
shows that in practice, server implementations may fail to fully stop
these attacks due to the complexity of this mitigation [ROBOT]. For
TLS 1.2 servers that support RSA key exchange using a DC-enabled end-
entity certificate, a hypothetical signature forgery attack would
allow forging a signature over a delegated credential. The forged
delegated credential could then be used by the attacker as the
equivalent of a man-in-the-middle certificate, valid for a maximum of
7 days.
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Server operators should therefore minimize the risk of using DC-
enabled end-entity certificates where a signature forgery oracle may
be present. If possible, server operators may choose to use DC-
enabled certificates only for signing credentials, and not for
serving non-DC TLS traffic. Furthermore, server operators may use
elliptic curve certificates for DC-enabled traffic, while using RSA
certificates without the DelegationUsage certificate extension for
non-DC traffic; this completely prevents such attacks.
Note that if a signature can be forged over an arbitrary credential,
the attacker can choose any value for the valid_time field. Repeated
signature forgeries therefore allow the attacker to create multiple
delegated credentials that can cover the entire validity period of
the certificate. Temporary exposure of the key or a signing oracle
may allow the attacker to impersonate a server for the lifetime of
the certificate.
8. Acknowledgements
Thanks to David Benjamin, Christopher Patton, Kyle Nekritz, Anirudh
Ramachandran, Benjamin Kaduk, Kazuho Oku, Daniel Kahn Gillmor, Watson
Ladd, Robert Merget, Juraj Somorovsky, Nimrod Aviram for their
discussions, ideas, and bugs they have found.
9. References
9.1. 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/info/rfc2119>.
[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/info/rfc5280>.
[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>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.
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[X.680] ITU-T, "Information technology - Abstract Syntax Notation
One (ASN.1): Specification of basic notation", ISO/
IEC 8824-1:2015, November 2015.
[X.690] ITU-T, "Information technology - ASN.1 encoding Rules:
Specification of Basic Encoding Rules (BER), Canonical
Encoding Rules (CER) and Distinguished Encoding Rules
(DER)", ISO/IEC 8825-1:2015, November 2015.
9.2. Informative References
[BLEI] Bleichenbacher, D., "Chosen Ciphertext Attacks against
Protocols Based on RSA Encryption Standard PKCS #1",
Advances in Cryptology -- CRYPTO'98, LNCS vol. 1462,
pages: 1-12 , 1998.
[KEYLESS] Sullivan, N. and D. Stebila, "An Analysis of TLS Handshake
Proxying", IEEE Trustcom/BigDataSE/ISPA 2015 , 2015.
[RFC3820] Tuecke, S., Welch, V., Engert, D., Pearlman, L., and M.
Thompson, "Internet X.509 Public Key Infrastructure (PKI)
Proxy Certificate Profile", RFC 3820,
DOI 10.17487/RFC3820, June 2004,
<https://www.rfc-editor.org/info/rfc3820>.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008,
<https://www.rfc-editor.org/info/rfc5246>.
[RFC5912] Hoffman, P. and J. Schaad, "New ASN.1 Modules for the
Public Key Infrastructure Using X.509 (PKIX)", RFC 5912,
DOI 10.17487/RFC5912, June 2010,
<https://www.rfc-editor.org/info/rfc5912>.
[RFC8032] Josefsson, S. and I. Liusvaara, "Edwards-Curve Digital
Signature Algorithm (EdDSA)", RFC 8032,
DOI 10.17487/RFC8032, January 2017,
<https://www.rfc-editor.org/info/rfc8032>.
[RFC8555] Barnes, R., Hoffman-Andrews, J., McCarney, D., and J.
Kasten, "Automatic Certificate Management Environment
(ACME)", RFC 8555, DOI 10.17487/RFC8555, March 2019,
<https://www.rfc-editor.org/info/rfc8555>.
[ROBOT] Boeck, H., Somorovsky, J., and C. Young, "Return Of
Bleichenbacher's Oracle Threat (ROBOT)", 27th USENIX
Security Symposium , 2018.
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[XPROT] Jager, T., Schwenk, J., and J. Somorovsky, "On the
Security of TLS 1.3 and QUIC Against Weaknesses in PKCS#1
v1.5 Encryption", Proceedings of the 22nd ACM SIGSAC
Conference on Computer and Communications Security , 2015.
Appendix A. ASN.1 Module
The following ASN.1 module provides the complete definition of the
DelegationUsage certificate extension. The ASN.1 module makes
imports from [RFC5912].
DelegatedCredentialExtn
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-delegated-credential-extn(TBD) }
DEFINITIONS IMPLICIT TAGS ::=
BEGIN
-- EXPORT ALL
IMPORTS
EXTENSION
FROM PKIX-CommonTypes-2009 -- From RFC 5912
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-pkixCommon-02(57) } ;
-- OID
id-cloudflare OBJECT IDENTIFIER ::=
{ iso(1) identified-organization(3) dod(6) internet(1) private(4)
enterprise(1) 44363 }
-- EXTENSION
ext-delegationUsage EXTENSION ::=
{ SYNTAX DelegationUsage
IDENTIFIED BY id-pe-delegationUsage }
id-pe-delegationUsage OBJECT IDENTIFIER ::= { id-cloudflare 44 }
DelegationUsage ::= NULL
END
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Appendix B. Example Certificate
The following certificate has the Delegated Credentials OID.
-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----
Authors' Addresses
Richard Barnes
Cisco
Email: rlb@ipv.sx
Subodh Iyengar
Facebook
Email: subodh@fb.com
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Nick Sullivan
Cloudflare
Email: nick@cloudflare.com
Eric Rescorla
Mozilla
Email: ekr@rtfm.com
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