Symptom: When using larger hash functions and short messages,
these six blocks take too much time to be conditionally copied.
Observations:
- SHA-384 consumes more data per iteration, unlike SHA-256.
- The value of `kVarianceBlocks` must depend on the parameters
of the selected hash algorithm.
- Avoid magic constants.
Changes:
- A new formula for the kVarianceBlocks value.
- Stronger test vectors were created in change: 32724.
- The new formula passes these tests.
Discussion:
OpenSSL team: https://github.com/openssl/openssl/pull/7342
Quoting mattcaswell:
> The "real" data that needs to be hashed has to be padded for the
> hashing algorithm. For SHA1 the smallest amount of padding that
> can be added is the "0x80" byte plus 8 bytes containing the message
> length, i.e. 9 bytes. If the data length is within 9 bytes of the
> end of the hash block boundary then the padding will push it into
> an extra block to be hashed.
Change-Id: Id1ad2389927014316eed2b453aac6e4c2a585c5c
Reviewed-on: https://boringssl-review.googlesource.com/c/32624
Reviewed-by: Adam Langley <agl@google.com>
Reviewed-by: David Benjamin <davidben@google.com>
Commit-Queue: Adam Langley <agl@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>
144d924e0b