Implement DSA_SIG_set0() and ECDSA_SIG_set0(), for setting signature values.

SSH2 implementations which use DSA_do_verify() and ECDSA_do_verify() are given
the R and S values, and the data to be signed, by the client.  Thus in order
to validate these signatures, SSH2 implementations will digest and sign
the data -- and then pass in properly provisioned DSA_SIG and ECDSA_SIG objects.

Unfortunately, the existing OpenSSL-1.1.0 APIs do not allow for directly setting
those R and S values in these objects, which makes using OpenSSL for such
SSH2 implementations much more difficult.

Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Emilia Käsper <emilia@openssl.org>
Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/1193)

1 files changed, 9 insertions, 0 deletions

diff --git a/crypto/ec/ec_asn1.c b/crypto/ec/ec_asn1.c
index 9272e1f1ba..89cc67d8aa 100644
--- a/crypto/ec/ec_asn1.c
+++ b/crypto/ec/ec_asn1.c
@@ -1180,6 +1180,15 @@ void ECDSA_SIG_get0(BIGNUM **pr, BIGNUM **ps, const ECDSA_SIG *sig)
         *ps = sig->s;
 }
 
+int ECDSA_SIG_set0(BIGNUM *r, BIGNUM *s, ECDSA_SIG *sig)
+{
+    BN_clear_free(sig->r);
+    BN_clear_free(sig->s);
+    sig->r = r;
+    sig->s = s;
+    return 1;
+}
+
 int ECDSA_size(const EC_KEY *r)
 {
     int ret, i;