Additional verification regarding EC signatures #412
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ocheron
commented
Jan 6, 2020
ocheron
commented
- Prevents to use EdDSA with TLS10 and TLS11. EdDSA support is signaled through "signature_algorithms" only, so needs TLS12 or later for proper negotiation between client and server.
- For TLS13, verifies that the received elliptic curve matches the hash algorithm chosen by peer (i.e. SHA-256 is for P-256, SHA-384 is for P-384, etc.)
- For TLS12 or before, verifies that the elliptic curve used to generate an ECDSA signature matches sent extension "Supported Elliptic Curves"
- For uniform behavior, make sure we call isDigitalSignaturePair before TLS12 too
EdDSA support is only signaled through "signature_algorithms" so needs TLS12 for proper negotiation between client and server.
Starting with TLS13, the hash in the "signature_algorithm" value must be compatible with the elliptic curve used to generate the signature. This commit adds the verification.
For TLS 1.2 and below, a client verifying an ECDSA signature now checks that the elliptic curve used to generate the signature is part of the supported curves it previously announced in the extension. As consequence, elliptic curves that are not P-256, P-384, P-521 are not accepted anymore.
kazu-yamamoto
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Jan 7, 2020
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