Do not allow using SSH_DIGEST_AUTO for any algorithm other than
ed25519.
Do not allow using incompatible hash algorithms when signing or
verifying signatures.
Added negative tests for all combinations of signature and hash
algorithms.
Signed-off-by: Anderson Toshiyuki Sasaki <ansasaki@redhat.com>
Reviewed-by: Jakub Jelen <jjelen@redhat.com>
Reviewed-by: Andreas Schneider <asn@cryptomilk.org>