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maddeleine
commented
Feb 16, 2026
| /* "default_fips" */ | ||
| { | ||
| const struct s2n_security_policy *versioned_policies[] = { | ||
| &security_policy_20240416, |
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So, if you're wondering what's happening here, basically, this security policy only advertises support for two signature curves, p256 and p384. And this test checks all cert permutations, which means that it will try to negotiate with a p521 curve, which now fails. Unfortunately s2n_test_cert_chains_set_supported doesn't allow you to mark specific curve types as being not supported. I'm not really sure if it's worth the effort to add that in.
jmayclin
reviewed
Feb 17, 2026
jmayclin
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Feb 17, 2026
CarolYeh910
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Feb 18, 2026
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Goal
Adds additional verification checks to ECDSA curves.
Why
s2n-tls did not verify which specific curve was used in a cert verify/key exchange message. We consider this a bug rather than a security issue given how unrealistic signature spoofing would be within the timeframe of a TLS handshake.
How
Adds checks to make sure that we are correctly verifying which curve is used for a peer's signature in the TLS1.2 and TLS.13 codepaths.
Callouts
There exists a slight mismatch here, an s2n-tls server will still use whichever certificate it has on hand, as long as the signature type is supported by the peer. We probably should fix that behavior as well on the server side.
Testing
Adds unit tests for both TLS1.2 and TLS1.3
Related
release summary: s2n-tls now errors if a peer sent an ECDSA signature with a mislabeled curve.
By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.