Previously, servers could set SSL_OP_CIPHER_SERVER_PREFERENCE to
configure behavior where the server's own preferences for TLS curves
(supported_groups) are prioritized over the client's. Since servers can
configure equipreference groups in their own preference lists to allow
client preferences to be partially respected, there is little reason not
to always prioritize the server's preference.
This CL makes the SSL_OP_CIPHER_SERVER_PREFERENCE behavior always
enabled for TLS curves, and setting the SSL_OP_CIPHER_SERVER_PREFERENCE
option is now a no-op for TLS curves (supported_groups).
There is no change yet to TLS 1.2 ciphers, which still require
SSL_OP_CIPHER_SERVER_PREFERENCE to enable prioritization of server
preference.
Update-Note: SSL_OP_CIPHER_SERVER_PREFERENCE is now a no-op for TLS
curves (supported_groups), and its behavior is always enabled. That is,
for a server, the server's own preferences are prioritized over the
client's. Callers that want the old default behavior for TLS curves can
use `SSL_CTX_set1_group_ids_with_flags` and configure every group into a
single equipreference group, but this is not recommended.
Bug: 550356540
Change-Id: If1655413e62dea779f3c970aa6cfff4e6a6a6964
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/104728
Commit-Queue: Lily Chen <chlily@google.com>
Reviewed-by: David Benjamin <davidben@google.com>
Lily Chen
e651545da6