Using TLS in Applications R. Salz
Internet-Draft Akamai Technologies
Updates: 9325 (if approved) N. Aviram
Intended status: Best Current Practice 26 February 2025
Expires: 30 August 2025
New Protocols Must Require TLS 1.3
draft-ietf-uta-require-tls13-06
Abstract
TLS 1.2 is in use and can be configured such that it provides good
security properties. TLS 1.3 use is increasing, and fixes some known
deficiencies with TLS 1.2, such as removing error-prone cryptographic
primitives and encrypting more of the traffic so that it is not
readable by outsiders. For these reasons, new protocols must require
and assume the existence of TLS 1.3. As DTLS 1.3 is not widely
available or deployed, this prescription does not pertain to DTLS (in
any DTLS version); it pertains to TLS only.
This document updates RFC9325.
About This Document
This note is to be removed before publishing as an RFC.
Status information for this document may be found at
https://datatracker.ietf.org/doc/draft-ietf-uta-require-tls13/.
Discussion of this document takes place on the Using TLS in
Applications Working Group mailing list (mailto:uta@ietf.org), which
is archived at https://mailarchive.ietf.org/arch/browse/uta/.
Subscribe at https://www.ietf.org/mailman/listinfo/uta/.
Source for this draft and an issue tracker can be found at
https://github.com/richsalz/draft-use-tls13.
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-
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 3
3. Implications for post-quantum cryptography . . . . . . . . . 3
4. TLS Use by Other Protocols and Applications . . . . . . . . . 3
5. Changes to RFC 9325 . . . . . . . . . . . . . . . . . . . . . 4
6. Security Considerations . . . . . . . . . . . . . . . . . . . 4
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
8.1. Normative References . . . . . . . . . . . . . . . . . . 5
8.2. Informative References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
TLS 1.2 [TLS12] is in use and can be configured such that it provides
good security properties. However, this protocol version suffers
from several deficiencies, as described in Section 6. Note that
addressing them usually requires bespoke configuration.
TLS 1.3 [TLS13] is also in widespread use and fixes most known
deficiencies with TLS 1.2, such as encrypting more of the traffic so
that it is not readable by outsiders and removing most cryptographic
primitives considered dangerous. Importantly, TLS 1.3 enjoys robust
security proofs and provides excellent security without any
additional configuration.
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This document specifies that, since TLS 1.3 use is widespread, new
protocols must require and assume its existence. It updates
[RFC9325] as described in Section 5. As DTLS 1.3 is not widely
available or deployed, this prescription does not pertain to DTLS (in
any DTLS version); it pertains to TLS only.
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. Implications for post-quantum cryptography
Cryptographically-relevant quantum computers (CRQC), once available,
will have a huge impact on TLS traffic. To mitigate this, TLS
applications will need to migrate to post-quantum cryptography (PQC)
[PQC]. Detailed consideration of when any application requires PQC,
or when a CRQC is a threat they need to protect against, is beyond
the scope of this document.
For TLS it is important to note that the focus of these efforts is
TLS 1.3 or later, and that TLS 1.2 will not be supported (see
[TLS12FROZEN]). This is one more reason for new protocols to default
to TLS 1.3, where PQC is actively being standardized, as this gives
new applications the option to use PQC.
4. TLS Use by Other Protocols and Applications
Any new protocol that uses TLS MUST specify as its default TLS 1.3.
For example, QUIC [QUICTLS] requires TLS 1.3 and specifies that
endpoints MUST terminate the connection if an older version is used.
If deployment considerations are a concern, the protocol MAY specify
TLS 1.2 as an additional, non-default option. As a counter example,
the Usage Profile for DNS over TLS [DNSTLS] specifies TLS 1.2 as the
default, while also allowing TLS 1.3. For newer specifications that
choose to support TLS 1.2, those preferences are to be reversed.
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The initial TLS handshake allows a client to specify which versions
of the TLS protocol it supports and the server is intended to pick
the highest version that it also supports. This is known as the "TLS
version negotiation," and many TLS libraries provide a way for
applications to specify the range of versions. When the API allows
it, clients SHOULD specify just the minimum version they want. This
MUST be TLS 1.3 or TLS 1.2, depending on the circumstances described
in the above paragraphs.
5. Changes to RFC 9325
RFC 9325 provides recommendations for ensuring the security of
deployed services that use TLS and, unlike this document, DTLS as
well. At this time it was published, it described availability of
TLS 1.3 as "widely available." The transition and adoption mentioned
in that documnent has grown, and this document now makes two small
changes to the recommendations in [RFC9325], Section 3.1.1:
* That section says that TLS 1.3 SHOULD be supported; this document
says that for new protocols it MUST be supported.
* That section says that TLS 1.2 MUST be supported; this document
says that it MAY be supported as described above.
Again, these changes only apply to TLS, and not DTLS.
6. Security Considerations
TLS 1.2 was specified with several cryptographic primitives and
design choices that have, over time, weakened its security. The
purpose of this section is to briefly survey several such prominent
problems that have affected the protocol. It should be noted,
however, that TLS 1.2 can be configured securely; it is merely much
more difficult to configure it securely as opposed to using its
modern successor, TLS 1.3. See [RFC9325] for a more thorough guide
on the secure deployment of TLS 1.2.
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Firstly, the TLS 1.2 protocol, without any extension points, is
vulnerable to renegotiation attacks (see [RENEG1] and [RENEG2]) and
the Triple Handshake attack (see [TRIPLESHAKE]). Broadly, these
attacks exploit the protocol's support for renegotiation in order to
inject a prefix chosen by the attacker into the plaintext stream.
This is usually a devastating threat in practice, that allows e.g.
obtaining secret cookies in a web setting. In light of the above
problems, [RFC5746] specifies an extension that prevents this
category of attacks. To securely deploy TLS 1.2, either
renegotiation must be disabled entirely, or this extension must be
used. Additionally, clients must not allow servers to renegotiate
the certificate during a connection.
Secondly, the original key exchange methods specified for the
protocol, namely RSA key exchange and finite field Diffie-Hellman,
suffer from several weaknesses. Similarly, to securely deploy the
protocol, these key exchange methods must be disabled. See
[I-D.draft-ietf-tls-deprecate-obsolete-kex] for details.
Thirdly, symmetric ciphers which were widely-used in the protocol,
namely RC4 and CBC cipher suites, suffer from several weaknesses.
RC4 suffers from exploitable biases in its key stream; see [RFC7465].
CBC cipher suites have been a source of vulnerabilities throughout
the years. A straightforward implementation of these cipher suites
inherently suffers from the Lucky13 timing attack [LUCKY13]. The
first attempt to implement the cipher suites in constant time
introduced an even more severe vulnerability [LUCKY13FIX]. There
have been further similar vulnerabilities throughout the years
exploiting CBC cipher suites; refer to e.g. [CBCSCANNING] for an
example and a survey of similar works.
In addition, TLS 1.2 was affected by several other attacks that TLS
1.3 is immune to: BEAST [BEAST], Logjam [WEAKDH], FREAK [FREAK], and
SLOTH [SLOTH].
And finally, while application layer traffic is always encrypted,
most of the handshake messages are not. Therefore, the privacy
provided is suboptimal. This is a protocol issue that cannot be
addressed by configuration.
7. IANA Considerations
This document makes no requests to IANA.
8. References
8.1. Normative References
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[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>.
[RFC9325] Sheffer, Y., Saint-Andre, P., and T. Fossati,
"Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 9325, DOI 10.17487/RFC9325, November
2022, <https://www.rfc-editor.org/rfc/rfc9325>.
[TLS12] 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/rfc/rfc5246>.
[TLS12FROZEN]
Salz, R. and N. Aviram, "TLS 1.2 is in Feature Freeze",
Work in Progress, Internet-Draft, draft-ietf-tls-tls12-
frozen-06, 29 January 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-tls-
tls12-frozen-06>.
[TLS13] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", Work in Progress, Internet-Draft, draft-
ietf-tls-rfc8446bis-12, 17 February 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-tls-
rfc8446bis-12>.
8.2. Informative References
[BEAST] Duong, T. and J. Rizzo, "Here come the xor ninjas", n.d.,
<http://www.hpcc.ecs.soton.ac.uk/dan/talks/bullrun/
Beast.pdf>.
[CBCSCANNING]
Merget, R., Somorovsky, J., Aviram, N., Young, C.,
Fliegenschmidt, J., Schwenk, J., and Y. Shavitt, "Scalable
Scanning and Automatic Classification of TLS Padding
Oracle Vulnerabilities", n.d.,
<https://www.usenix.org/system/files/sec19-merget.pdf>.
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[DNSTLS] Dickinson, S., Gillmor, D., and T. Reddy, "Usage Profiles
for DNS over TLS and DNS over DTLS", RFC 8310,
DOI 10.17487/RFC8310, March 2018,
<https://www.rfc-editor.org/rfc/rfc8310>.
[FREAK] Beurdouche, B., Bhargavan, K., Delignat-Lavaud, A.,
Fournet, C., Kohlweiss, M., Pironti, A., Strub, P.-Y., and
J. K. Zinzindohoue, "A messy state of the union: Taming
the composite state machines of TLS", n.d.,
<https://inria.hal.science/hal-01114250/file/messy-state-
of-the-union-oakland15.pdf>.
[I-D.draft-ietf-tls-deprecate-obsolete-kex]
Bartle, C. and N. Aviram, "Deprecating Obsolete Key
Exchange Methods in TLS 1.2", Work in Progress, Internet-
Draft, draft-ietf-tls-deprecate-obsolete-kex-05, 3
September 2024, <https://datatracker.ietf.org/doc/html/
draft-ietf-tls-deprecate-obsolete-kex-05>.
[LUCKY13] Al Fardan, N. J. and K. G. Paterson, "Lucky Thirteen:
Breaking the TLS and DTLS record protocols", n.d.,
<http://www.isg.rhul.ac.uk/tls/TLStiming.pdf>.
[LUCKY13FIX]
Somorovsky, J., "Systematic fuzzing and testing of TLS
libraries", n.d., <https://nds.rub.de/media/nds/
veroeffentlichungen/2016/10/19/tls-attacker-ccs16.pdf>.
[PQC] "What Is Post-Quantum Cryptography?", August 2024,
<https://www.nist.gov/cybersecurity/what-post-quantum-
cryptography>.
[QUICTLS] Thomson, M., Ed. and S. Turner, Ed., "Using TLS to Secure
QUIC", RFC 9001, DOI 10.17487/RFC9001, May 2021,
<https://www.rfc-editor.org/rfc/rfc9001>.
[RENEG1] Rescorla, E., "Understanding the TLS Renegotiation
Attack", n.d.,
<https://web.archive.org/web/20091231034700/
http://www.educatedguesswork.org/2009/11/
understanding_the_tls_renegoti.html>.
[RENEG2] Ray, M., "Authentication Gap in TLS Renegotiation", n.d.,
<https://web.archive.org/web/20091228061844/
http://extendedsubset.com/?p=8>.
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[RFC5746] Rescorla, E., Ray, M., Dispensa, S., and N. Oskov,
"Transport Layer Security (TLS) Renegotiation Indication
Extension", RFC 5746, DOI 10.17487/RFC5746, February 2010,
<https://www.rfc-editor.org/rfc/rfc5746>.
[RFC7465] Popov, A., "Prohibiting RC4 Cipher Suites", RFC 7465,
DOI 10.17487/RFC7465, February 2015,
<https://www.rfc-editor.org/rfc/rfc7465>.
[SLOTH] Bhargavan, K. and G. Leurent, "Transcript collision
attacks: Breaking authentication in TLS, IKE, and SSH",
n.d., <https://inria.hal.science/hal-01244855/file/
SLOTH_NDSS16.pdf>.
[TRIPLESHAKE]
"Triple Handshakes Considered Harmful Breaking and Fixing
Authentication over TLS", n.d.,
<https://mitls.org/pages/attacks/3SHAKE>.
[WEAKDH] Adrian, D., Bhargavan, K., Durumeric, Z., Gaudry, P.,
Green, M., Halderman, J. A., Heninger, N., Springall, D.,
Thomé, E., Valenta, L., and B. VanderSloot, "Imperfect
forward secrecy: How Diffie-Hellman fails in practice",
n.d.,
<https://dl.acm.org/doi/pdf/10.1145/2810103.2813707>.
Authors' Addresses
Rich Salz
Akamai Technologies
Email: rsalz@akamai.com
Nimrod Aviram
Email: nimrod.aviram@gmail.com
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