Add aes_gmac() as a wrapper for AES GMAC operations using GCM

This is otherwise identical to aes_gcm_ae() but does not use the
plain/crypt pointers since no data is encrypted.

Signed-hostap: Jouni Malinen <j@w1.fi>

src/crypto/aes-gcm.c

@@ -311,3 +311,11 @@ int aes_gcm_ad(const u8 *key, size_t key_len, const u8 *iv, size_t iv_len,
 
 	return 0;
 }
+
+
+int aes_gmac(const u8 *key, size_t key_len, const u8 *iv, size_t iv_len,
+	     const u8 *aad, size_t aad_len, u8 *tag)
+{
+	return aes_gcm_ae(key, key_len, iv, iv_len, NULL, 0, aad, aad_len, NULL,
+			  tag);
+}

src/crypto/aes_wrap.h

@@ -49,5 +49,8 @@ int __must_check aes_gcm_ad(const u8 *key, size_t key_len,
 			    const u8 *crypt, size_t crypt_len,
 			    const u8 *aad, size_t aad_len, const u8 *tag,
 			    u8 *plain);
+int __must_check aes_gmac(const u8 *key, size_t key_len,
+			  const u8 *iv, size_t iv_len,
+			  const u8 *aad, size_t aad_len, u8 *tag);
 
 #endif /* AES_WRAP_H */

tests/test-aes.c

@@ -407,6 +407,20 @@ static int test_gcm(void)
 			ret++;
 		}
 
+		if (p_len == 0) {
+			if (aes_gmac(k, k_len, iv, iv_len, aad, aad_len, tag) <
+			    0) {
+				printf("GMAC failed (test case %d)\n", i);
+				ret++;
+				continue;
+			}
+
+			if (os_memcmp(tag, t, sizeof(tag)) != 0) {
+				printf("GMAC tag mismatch (test case %d)\n", i);
+				ret++;
+			}
+		}
+
 		if (aes_gcm_ad(k, k_len, iv, iv_len, c, p_len, aad, aad_len,
 			       t, tmp) < 0) {
 			printf("GCM-AD failed (test case %d)\n", i);