Note that this structure has a weak pointer to the key, which was a
problem corrected in the AES-GCM code in
0f8bfdeb33. Also, it uses |void *|
instead of |const AES_KEY *| to refer to that key.
Change-Id: I70e632e3370ab27eb800bc1c0c64d2bd36b7cafb
Reviewed-on: https://boringssl-review.googlesource.com/7123
Reviewed-by: David Benjamin <davidben@google.com>