Add SSL_CIPHER_is_static_RSA.

Change-Id: Id0013a2441da206b051a05a39aa13e4eca937e03
Reviewed-on: https://boringssl-review.googlesource.com/13109
Reviewed-by: Adam Langley <agl@google.com>

include/openssl/ssl.h

@@ -1195,6 +1195,10 @@ OPENSSL_EXPORT int SSL_CIPHER_is_DHE(const SSL_CIPHER *cipher);
 /* SSL_CIPHER_is_ECDHE returns one if |cipher| uses ECDHE. */
 OPENSSL_EXPORT int SSL_CIPHER_is_ECDHE(const SSL_CIPHER *cipher);
 
+/* SSL_CIPHER_is_static_RSA returns one if |cipher| uses the static RSA key
+ * exchange. */
+OPENSSL_EXPORT int SSL_CIPHER_is_static_RSA(const SSL_CIPHER *cipher);
+
 /* SSL_CIPHER_get_min_version returns the minimum protocol version required
  * for |cipher|. */
 OPENSSL_EXPORT uint16_t SSL_CIPHER_get_min_version(const SSL_CIPHER *cipher);

ssl/ssl_cipher.c

@@ -1525,6 +1525,10 @@ int SSL_CIPHER_is_ECDHE(const SSL_CIPHER *cipher) {
   return (cipher->algorithm_mkey & SSL_kECDHE) != 0;
 }
 
+int SSL_CIPHER_is_static_RSA(const SSL_CIPHER *cipher) {
+  return (cipher->algorithm_mkey & SSL_kRSA) != 0;
+}
+
 uint16_t SSL_CIPHER_get_min_version(const SSL_CIPHER *cipher) {
   if (cipher->algorithm_mkey == SSL_kGENERIC ||
       cipher->algorithm_auth == SSL_aGENERIC) {