crypto/tls: disable CBC cipher suites with SHA-256 by default
As is, they were fully vulnerable to the Lucky13 attack. The SHA1
variants implement limited countermeasures (see
f28cf8346c4) but the
SHA256 ones are apparently used rarely enough (see
8741504888b) that
it's not worth the extra code.
Instead, disable them by default and update the warning.
Updates #13385
Updates #15487
Change-Id: I45b8b716001e2fa0811b17e25be76e2512e5abb2
Reviewed-on: https://go-review.googlesource.com/35290
Reviewed-by: Adam Langley <alangley@gmail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Matt Layher <mdlayher@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>