crypto.hmac: set the recommended key size to the block size #15031
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HMAC supports arbitrary key sizes, and there are no practical reasons to use more than 256 bit keys. In still make sense to match the security level, though, especially since a distinction between the block size and the key size can be confusing. Using HMAC.key_size instead of HMAC.mac_size caused our TLS implementation to compute wrong shared secrets when SHA-384 was used. So, fix it directly in `crypto.hmac` in order to prevent other misuses.
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…15031) HMAC supports arbitrary key sizes, and there are no practical reasons to use more than 256 bit keys. It still makes sense to match the security level, though, especially since a distinction between the block size and the key size can be confusing. Using HMAC.key_size instead of HMAC.mac_size caused our TLS implementation to compute wrong shared secrets when SHA-384 was used. So, fix it directly in `crypto.hmac` in order to prevent other misuses.
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HMAC supports arbitrary key sizes, and there are no practical reasons to use more than 256 bit keys.
It still make sense to match the security level, though, especially since a distinction between the block size and the key size can be confusing.
Using
HMAC.key_sizeinstead ofHMAC.mac_sizecaused our TLS implementation to compute wrong shared secrets when SHA-384 was used. So, fix it directly incrypto.hmacin order to prevent other misuses.