Remove dependency from SSL on PK internals

So far, with MBEDTLS_SSL_KEEP_PEER_CERTIFICATE disabled, the SSL module relied
on a undocumented feature of the PK module: that you can distinguish between
contexts that have been setup and context that haven't. This feature is going
to go away in the case of PK_SINGLE_TYPE, as we'll soon (as in: the next
commit does that) no longer be storing the (now two-valued) pk_info member.

Note even with this change, we could still distinguish if the context has been
set up by look if pk_ctx is NULL or not, but this is also going away in the
near future (a few more commits down the road), so not a good option either.

include/mbedtls/ssl_internal.h

@@ -382,9 +382,9 @@ struct mbedtls_ssl_sig_hash_set_t
  */
 struct mbedtls_ssl_handshake_params
 {
-    /*
+#if !defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)
-     * Handshake specific crypto variables
+    uint8_t got_peer_pubkey;            /*!< Did we store the peer's public key from its certificate? */
-     */
+#endif /* !MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
 #if defined(MBEDTLS_SSL_PROTO_DTLS)
     unsigned char verify_cookie_len;    /*!<  Cli: cookie length
                                               Srv: flag for sending a cookie */

library/ssl_cli.c

@@ -2379,11 +2379,7 @@ static int ssl_rsa_encrypt_partial_pms( mbedtls_ssl_context *ssl,
     }
 
 #if !defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)
-    /* Because the peer CRT pubkey is embedded into the handshake
+    if( ssl->handshake->got_peer_pubkey )
-     * params currently, and there's no 'is_init' functions for PK
-     * contexts, we need to break the abstraction and peek into
-     * the PK context to see if it has been initialized. */
-    if( ssl->handshake->peer_pubkey.pk_info != MBEDTLS_PK_INVALID_HANDLE )
         peer_pk = &ssl->handshake->peer_pubkey;
 #else /* !MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
     if( ssl->session_negotiate->peer_cert != NULL )

library/ssl_srv.c

@@ -4454,15 +4454,10 @@ static int ssl_parse_certificate_verify( mbedtls_ssl_context *ssl )
     /* Skip if we haven't received a certificate from the client.
      * If MBEDTLS_SSL_KEEP_PEER_CERTIFICATE is set, this can be
      * inferred from the setting of mbedtls_ssl_session::peer_cert.
-     * If MBEDTLS_SSL_KEEP_PEER_CERTIFICATE is not set, it can
+     * If MBEDTLS_SSL_KEEP_PEER_CERTIFICATE is not set, it is tracked in a
-     * be inferred from whether we've held back the peer CRT's
+     * specific variable. */
-     * public key in mbedtls_ssl_handshake_params::peer_pubkey. */
 #if !defined(MBEDTLS_SSL_KEEP_PEER_CERTIFICATE)
-    /* Because the peer CRT pubkey is embedded into the handshake
+    if( ssl->handshake->got_peer_pubkey )
-     * params currently, and there's no 'is_init' functions for PK
-     * contexts, we need to break the abstraction and peek into
-     * the PK context to see if it has been initialized. */
-    if( ssl->handshake->peer_pubkey.pk_info != MBEDTLS_PK_INVALID_HANDLE )
         peer_pk = &ssl->handshake->peer_pubkey;
 #else /* !MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */
     if( ssl->session_negotiate->peer_cert != NULL )

library/ssl_tls.c

@@ -7357,6 +7357,7 @@ static int ssl_remember_peer_pubkey( mbedtls_ssl_context *ssl,
         return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
     }
 
+    ssl->handshake->got_peer_pubkey = 1;
     return( 0 );
 }
 #endif /* !MBEDTLS_SSL_KEEP_PEER_CERTIFICATE */