It would be nice to have a single-shot EVP_CIPHER_CTX API. This function
is not it.
EVP_Cipher is absurd. It's actually just exposing the internal
EVP_CIPHER 'cipher' callback, whose calling convention is extremely
complex. We've currently documented it as a "single-shot" API, but it's
not single-shot either, as it does update cipher state. It just can't
update across block boundaries.
It is particularly bizarre for "custom ciphers", which include AEADs,
which completely changes the return value convention from
bytes_written/-1 to 1/0, but also adds a bunch of magic NULL behaviors:
- out == NULL, in != NULL: supply AAD
- out != NULL, in != NULL: bulk encrypt/decrypt
- out == NULL, in == NULL: compute/check the tag
Moreover, existing code, like OpenSSH, relies on this behavior. To
ensure we don't break it when refactoring EVP_CIPHER internals, capture
the current behavior in tests. But also, no one should be using this in
new code, so deprecate it.
Upstream hasn't quite deprecated it, they now say "Due to the
constraints of the API contract of this function it shouldn't be used in
applications, please consider using EVP_CipherUpdate() and
EVP_CipherFinal_ex() instead."
Bug: 494
Change-Id: Icfe39a8fbbc860b03c9861f4164b7ee8da340216
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/55391
Reviewed-by: Adam Langley <agl@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
Reviewed-by: Bob Beck <bbe@google.com>
David Benjamin
e40d0f8ee1