pki: Add a common place to store raw signatures

This is a preparation to store the raw signature for all algorithms in
the same place in ssh_signature.

Signed-off-by: Anderson Toshiyuki Sasaki <ansasaki@redhat.com>
Reviewed-by: Jakub Jelen <jjelen@redhat.com>
Reviewed-by: Andreas Schneider <asn@cryptomilk.org>

include/libssh/pki.h

@@ -88,6 +88,7 @@ struct ssh_signature_struct {
     struct mbedtls_ecdsa_sig ecdsa_sig;
 #endif /* HAVE_LIBGCRYPT */
     ed25519_signature *ed25519_sig;
+    ssh_string raw_sig;
 };
 
 typedef struct ssh_signature_struct *ssh_signature;

src/pki.c

@@ -629,6 +629,9 @@ void ssh_signature_free(ssh_signature sig)
             break;
     }
 
+    /* Explicitly zero the signature content before free */
+    ssh_string_burn(sig->raw_sig);
+    ssh_string_free(sig->raw_sig);
     SAFE_FREE(sig);
 }