tree 4a51bf5c5edc3bd26a56d35cd23b5b3a078ef598
parent 71666cb87c4de0bbc34df783e571bdc936f38b0b
author David Benjamin <davidben@google.com> 1523922882 -0400
committer Adam Langley <agl@google.com> 1525288916 +0000

Remove legacy SHA-2 CBC ciphers.

All CBC ciphers in TLS are broken and insecure. TLS 1.2 introduced
AEAD-based ciphers which avoid their many problems. It also introduced
new CBC ciphers based on HMAC-SHA256 and HMAC-SHA384 that share the same
flaws as the original HMAC-SHA1 ones. These serve no purpose. Old
clients don't support them, they have the highest overhead of all TLS
ciphers, and new clients can use AEADs anyway.

Remove them from libssl. This is the smaller, more easily reverted
portion of the removal. If it survives a week or so, we can unwind a lot
more code elsewhere in libcrypto. This removal will allow us to clear
some indirect calls from crypto/cipher_extra/tls_cbc.c, aligning with
the recommendations here:

https://github.com/HACS-workshop/spectre-mitigations/blob/master/crypto_guidelines.md#2-avoid-indirect-branches-in-constant-time-code

Update-Note: The following cipher suites are removed:
- TLS_RSA_WITH_AES_128_CBC_SHA256
- TLS_RSA_WITH_AES_256_CBC_SHA256
- TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA256
- TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA384
- TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256
- TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384

Change-Id: I7ade0fc1fa2464626560d156659893899aab6f77
Reviewed-on: https://boringssl-review.googlesource.com/27944
Reviewed-by: Adam Langley <agl@google.com>