I believe this is a remnant of DSA. The logic strangely fails to check for
failure and then goes out of its way to ERR_clear_error. I believe this is so
that keys that are missing parameters silently move on. This dates to
upstream's dfeab0689f69c0b4bd3480ffd37a9cacc2f17d9c, which is SSLeay 0.9.1b. At
that time, EVP_PKEY_copy_parameters only did anything for DSA. (Now it only
does anything for ECDSA.)
My read is that this comes from DSA in PKIX's "optional domain parameters"
craziness. RFC 3279 says:
If the DSA domain parameters are omitted from the SubjectPublicKeyInfo
AlgorithmIdentifier and the CA signed the subject certificate using a
signature algorithm other than DSA, then the subject's DSA domain parameters
are distributed by other means.
This was probably part of some weird thing where, if your certificate is
missing parameters, the server would know what to use based on the private key.
(Also this was making the malloc tests unhappy.)
Change-Id: I8d8122a9f50a19e2bbe067f311a8e2d30774935c
Reviewed-on: https://boringssl-review.googlesource.com/3484
Reviewed-by: Adam Langley <agl@google.com>
310db06b79