Internet DRAFT - draft-davidben-tls13-pkcs1
draft-davidben-tls13-pkcs1
Network Working Group D. Benjamin
Internet-Draft Google LLC
Intended status: Experimental A. Popov
Expires: 19 April 2024 Microsoft Corp.
17 October 2023
Legacy RSASSA-PKCS1-v1_5 codepoints for TLS 1.3
draft-davidben-tls13-pkcs1-01
Abstract
This document allocates code points for the use of RSASSA-PKCS1-v1_5
with client certificates in TLS 1.3. This removes an obstacle for
some deployments to migrate to TLS 1.3.
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://davidben.github.io/tls13-pkcs1/draft-davidben-
tls13-pkcs1.html. Status information for this document may be found
at https://datatracker.ietf.org/doc/draft-davidben-tls13-pkcs1/.
Source for this draft and an issue tracker can be found at
https://github.com/davidben/tls13-pkcs1.
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
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This Internet-Draft will expire on 19 April 2024.
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Copyright Notice
Copyright (c) 2023 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 (https://trustee.ietf.org/
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Please review these documents carefully, as they describe your rights
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 3
3. PKCS#1 v1.5 SignatureScheme Types . . . . . . . . . . . . . . 3
4. Security Considerations . . . . . . . . . . . . . . . . . . . 4
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
6.1. Normative References . . . . . . . . . . . . . . . . . . 5
6.2. Informative References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
TLS 1.3 [RFC8446] removed support for RSASSA-PKCS1-v1_5 [RFC8017] in
CertificateVerify messages in favor of RSASSA-PSS. While RSASSA-PSS
is a long-established signature algorithm, some legacy hardware
cryptographic devices lack support for it. While uncommon in TLS
servers, these devices are sometimes used by TLS clients for client
certificates.
For example, Trusted Platform Modules (TPMs) are ubiquitous hardware
cryptographic devices that are often used to protect TLS client
certificate private keys. However, a large number of TPMs are unable
to produce RSASSA-PSS signatures compatible with TLS 1.3. TPM
specifications prior to 2.0 did not define RSASSA-PSS support (see
Section 5.8.1 of [TPM12]). TPM 2.0 includes RSASSA-PSS, but only
those TPM 2.0 devices compatible with FIPS 186-4 can be relied upon
to use the salt length matching the digest length, as required for
compatibility with TLS 1.3 (see Appendix B.7 of [TPM2]).
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TLS connections that rely on such devices cannot migrate to TLS 1.3.
Staying on TLS 1.2 leaks the client certificate to network attackers
and additionally prevents such deployments from protecting traffic
against retroactive decryption by an attacker with a quantum
computer.
Moreover, TLS negotiates the protocol version before client
certificates, so clients and servers cannot smoothly transition
unaffected connections to TLS 1.3. As a result, this issue is not
limited to individual connections that use affected devices. It
prevents entire deployments from migrating to TLS 1.3. See Section 4
for further discussion.
This document allocates code points to use these legacy keys with
client certificates in TLS 1.3.
2. 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.
3. PKCS#1 v1.5 SignatureScheme Types
The following SignatureScheme values are defined for use with TLS
1.3.
enum {
rsa_pkcs1_sha256_legacy(0x0420),
rsa_pkcs1_sha384_legacy(0x0520),
rsa_pkcs1_sha512_legacy(0x0620),
} SignatureScheme;
The above code points indicate a signature algorithm using RSASSA-
PKCS1-v1_5 [RFC8017] with the corresponding hash algorithm as defined
in [SHS]. They are only defined for signatures in the client
CertificateVerify message and are not defined for use in other
contexts. In particular, servers intending to advertise support for
RSASSA-PKCS1-v1_5 signatures in the certificates themselves should
use the rsa_pkcs1_* constants defined in [RFC8446].
Clients MUST NOT advertise these values in the signature_algorithms
extension of the ClientHello. They MUST NOT accept these values in
the server CertificateVerify message.
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Servers that wish to support clients authenticating with legacy
RSASSA-PKCS1-v1_5-only keys MAY send these values in the
signature_algorithms extension of the CertificateRequest message and
accept them in the client CertificateVerify message. Servers MUST
NOT accept these code points if not offered in the CertificateRequest
message.
Clients with such legacy keys MAY negotiate the use of these
signature algorithms if offered by the server. Clients SHOULD NOT
negotiate them with keys that support RSASSA-PSS.
TLS implementations SHOULD disable these code points by default.
4. Security Considerations
Prior to this document, legacy RSA keys would prevent client
certificate deployments from adopting TLS 1.3. The new code points
allow such deployments to upgrade without replacing the keys. TLS
1.3 fixes a privacy flaw [PRIVACY] with client certificates, so
upgrading is a particular benefit to these deployments. TLS 1.3 is
also a prequisite for post-quantum key exchanges
[I-D.ietf-tls-hybrid-design], necessary for deployments to protect
traffic against retroactive decryption by an attacker with a quantum
computer.
Additionally, TLS negotiates protocol versions before client
certificates. Clients send ClientHellos without knowing whether the
server will request to authenticate with legacy keys. Conversely,
servers respond with a TLS version and CertificateRequest without
knowing if the client will then respond with a legacy key. If the
client and server, respectively, offer and negotiate TLS 1.3, the
connection will fail due to the legacy key, when it previously
succeeded at TLS 1.2.
To recover from this failure, one side must globally disable TLS 1.3
or the client must implement an external fallback. Disabling TLS 1.3
impacts connections that would otherwise be unaffected by this issue,
while external fallbacks break TLS's security analysis and may
introduce vulnerabilities [POODLE]. The new code points reduce the
pressure on implementations to select one of these problematic
mitigations and unblocks TLS 1.3 deployment.
At the same time, the new code points also reduce the pressure on
implementations to migrate to RSASSA-PSS. The above considerations
do not apply to server keys, so these new code points are forbidden
for use with server certificates. RSASSA-PSS continues to be
required for TLS 1.3 servers using RSA keys. This minimizes the
impact to only those cases necessary to unblock TLS 1.3 deployment.
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Finally, when implemented incorrectly, RSASSA-PKCS1-v1_5 admits
signature forgeries [MFSA201473]. Implementations producing or
verifying signatures with these algorithms MUST implement RSASSA-
PKCS1-v1_5 as specified in section 8.2 of [RFC8017]. In particular,
clients MUST include the mandatory NULL parameter in the DigestInfo
structure and produce a valid DER [X690] encoding. Servers MUST
reject signatures which do not meet these requirements.
5. IANA Considerations
IANA is requested to create the following entries in the TLS
SignatureScheme registry, defined in [RFC8446]. The "Recommended"
column should be set to "N", and the "Reference" column should be set
to this document.
+========+=========================+
| Value | Description |
+========+=========================+
| 0x0420 | rsa_pkcs1_sha256_legacy |
+--------+-------------------------+
| 0x0520 | rsa_pkcs1_sha384_legacy |
+--------+-------------------------+
| 0x0620 | rsa_pkcs1_sha512_legacy |
+--------+-------------------------+
Table 1
6. References
6.1. 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>.
[RFC8017] Moriarty, K., Ed., Kaliski, B., Jonsson, J., and A. Rusch,
"PKCS #1: RSA Cryptography Specifications Version 2.2",
RFC 8017, DOI 10.17487/RFC8017, November 2016,
<https://www.rfc-editor.org/rfc/rfc8017>.
[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>.
[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/rfc/rfc8446>.
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[SHS] Dang, Q., "Secure Hash Standard", National Institute of
Standards and Technology, DOI 10.6028/nist.fips.180-4,
July 2015, <https://doi.org/10.6028/nist.fips.180-4>.
[TPM12] Trusted Computing Group, "TPM Main Specification Level 2
Version 1.2, Revision 116, Part 2 - Structures of the
TPM", 1 March 2011, <https://trustedcomputinggroup.org/wp-
content/uploads/TPM-Main-Part-2-TPM-
Structures_v1.2_rev116_01032011.pdf>.
[TPM2] Trusted Computing Group, "Trusted Platform Module Library
Specification, Family 2.0, Level 00, Revision 01.59, Part
1: Architecture", 8 November 2019,
<https://trustedcomputinggroup.org/wp-content/uploads/
TCG_TPM2_r1p59_Part1_Architecture_pub.pdf>.
[X690] 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 8825-1:2002, 2002.
6.2. Informative References
[I-D.ietf-tls-hybrid-design]
Stebila, D., Fluhrer, S., and S. Gueron, "Hybrid key
exchange in TLS 1.3", Work in Progress, Internet-Draft,
draft-ietf-tls-hybrid-design-09, 7 September 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-tls-
hybrid-design-09>.
[MFSA201473]
Delignat-Lavaud, A., "RSA Signature Forgery in NSS", 23
September 2014, <https://www.mozilla.org/en-
US/security/advisories/mfsa2014-73/>.
[POODLE] Moeller, B., "This POODLE bites: exploiting the SSL 3.0
fallback", 14 October 2014,
<https://security.googleblog.com/2014/10/this-poodle-
bites-exploiting-ssl-30.html>.
[PRIVACY] Wachs, M., Scheitle, Q., and G. Carle, "Push away your
privacy: Precise user tracking based on TLS client
certificate authentication", IEEE, 2017 Network Traffic
Measurement and Analysis Conference (TMA),
DOI 10.23919/tma.2017.8002897, June 2017,
<https://doi.org/10.23919/tma.2017.8002897>.
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Authors' Addresses
David Benjamin
Google LLC
Email: davidben@google.com
Andrei Popov
Microsoft Corp.
Email: andreipo@microsoft.com
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