Share common GCM-AE and GCM-AD functionality

These operations are almost identical, so use common functions to
share the same implementation.

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

src/crypto/aes-gcm.c

@@ -172,29 +172,29 @@ static void aes_gctr(void *aes, const u8 *icb, const u8 *x, size_t xlen, u8 *y)
 }
 
 
-/**
- * aes_gcm_ae - GCM-AE_K(IV, P, A)
- */
-int aes_gcm_ae(const u8 *key, size_t key_len, const u8 *iv, size_t iv_len,
-	       const u8 *plain, size_t plain_len,
-	       const u8 *aad, size_t aad_len, u8 *crypt, u8 *tag)
+static void * aes_gcm_init_hash_subkey(const u8 *key, size_t key_len, u8 *H)
 {
-	u8 H[AES_BLOCK_SIZE];
-	u8 J0[AES_BLOCK_SIZE], J0inc[AES_BLOCK_SIZE];
-	u8 S[16], len_buf[16];
 	void *aes;
 
 	aes = aes_encrypt_init(key, key_len);
 	if (aes == NULL)
-		return -1;
+		return NULL;
 
-	/* 1. Generate hash subkey H = AES_K(0^128) */
-	os_memset(H, 0, sizeof(H));
+	/* Generate hash subkey H = AES_K(0^128) */
+	os_memset(H, 0, AES_BLOCK_SIZE);
 	aes_encrypt(aes, H, H);
-	wpa_hexdump_key(MSG_EXCESSIVE, "Hash subkey H for GHASH", H, sizeof(H));
+	wpa_hexdump_key(MSG_EXCESSIVE, "Hash subkey H for GHASH",
+			H, AES_BLOCK_SIZE);
+	return aes;
+}
+
+
+static void aes_gcm_prepare_j0(const u8 *iv, size_t iv_len, const u8 *H, u8 *J0)
+{
+	u8 len_buf[16];
 
 	if (iv_len == 12) {
-		/* 2. Prepare block J_0 = IV || 0^31 || 1 [len(IV) = 96] */
+		/* Prepare block J_0 = IV || 0^31 || 1 [len(IV) = 96] */
 		os_memcpy(J0, iv, iv_len);
 		os_memset(J0 + iv_len, 0, AES_BLOCK_SIZE - iv_len);
 		J0[AES_BLOCK_SIZE - 1] = 0x01;
@@ -209,31 +209,72 @@ int aes_gcm_ae(const u8 *key, size_t key_len, const u8 *iv, size_t iv_len,
 		WPA_PUT_BE64(len_buf + 8, iv_len * 8);
 		ghash(H, len_buf, sizeof(len_buf), J0);
 	}
+}
+
+
+static void aes_gcm_gctr(void *aes, const u8 *J0, const u8 *in, size_t len,
+			 u8 *out)
+{
+	u8 J0inc[AES_BLOCK_SIZE];
+
+	if (len == 0)
+		return;
 
-	/* 3. C = GCTR_K(inc_32(J_0), P) */
 	os_memcpy(J0inc, J0, AES_BLOCK_SIZE);
 	inc32(J0inc);
-	aes_gctr(aes, J0inc, plain, plain_len, crypt);
+	aes_gctr(aes, J0inc, in, len, out);
+}
+
+
+static void aes_gcm_ghash(const u8 *H, const u8 *aad, size_t aad_len,
+			  const u8 *crypt, size_t crypt_len, u8 *S)
+{
+	u8 len_buf[16];
 
 	/*
-	 * 4. u = 128 * ceil[len(C)/128] - len(C)
-	 *    v = 128 * ceil[len(A)/128] - len(A)
-	 * 5. S = GHASH_H(A || 0^v || C || 0^u || [len(A)]64 || [len(C)]64)
+	 * u = 128 * ceil[len(C)/128] - len(C)
+	 * v = 128 * ceil[len(A)/128] - len(A)
+	 * S = GHASH_H(A || 0^v || C || 0^u || [len(A)]64 || [len(C)]64)
 	 * (i.e., zero padded to block size A || C and lengths of each in bits)
 	 */
 	ghash_start(S);
 	ghash(H, aad, aad_len, S);
-	ghash(H, crypt, plain_len, S);
+	ghash(H, crypt, crypt_len, S);
 	WPA_PUT_BE64(len_buf, aad_len * 8);
-	WPA_PUT_BE64(len_buf + 8, plain_len * 8);
+	WPA_PUT_BE64(len_buf + 8, crypt_len * 8);
 	ghash(H, len_buf, sizeof(len_buf), S);
 
 	wpa_hexdump_key(MSG_EXCESSIVE, "S = GHASH_H(...)", S, 16);
+}
+
+
+/**
+ * aes_gcm_ae - GCM-AE_K(IV, P, A)
+ */
+int aes_gcm_ae(const u8 *key, size_t key_len, const u8 *iv, size_t iv_len,
+	       const u8 *plain, size_t plain_len,
+	       const u8 *aad, size_t aad_len, u8 *crypt, u8 *tag)
+{
+	u8 H[AES_BLOCK_SIZE];
+	u8 J0[AES_BLOCK_SIZE];
+	u8 S[16];
+	void *aes;
 
-	/* 6. T = MSB_t(GCTR_K(J_0, S)) */
+	aes = aes_gcm_init_hash_subkey(key, key_len, H);
+	if (aes == NULL)
+		return -1;
+
+	aes_gcm_prepare_j0(iv, iv_len, H, J0);
+
+	/* C = GCTR_K(inc_32(J_0), P) */
+	aes_gcm_gctr(aes, J0, plain, plain_len, crypt);
+
+	aes_gcm_ghash(H, aad, aad_len, crypt, plain_len, S);
+
+	/* T = MSB_t(GCTR_K(J_0, S)) */
 	aes_gctr(aes, J0, S, sizeof(S), tag);
 
-	/* 7. Return (C, T) */
+	/* Return (C, T) */
 
 	aes_encrypt_deinit(aes);
 
@@ -249,57 +290,22 @@ int aes_gcm_ad(const u8 *key, size_t key_len, const u8 *iv, size_t iv_len,
 	       const u8 *aad, size_t aad_len, const u8 *tag, u8 *plain)
 {
 	u8 H[AES_BLOCK_SIZE];
-	u8 J0[AES_BLOCK_SIZE], J0inc[AES_BLOCK_SIZE];
-	u8 S[16], T[16], len_buf[16];
+	u8 J0[AES_BLOCK_SIZE];
+	u8 S[16], T[16];
 	void *aes;
 
-	aes = aes_encrypt_init(key, key_len);
+	aes = aes_gcm_init_hash_subkey(key, key_len, H);
 	if (aes == NULL)
 		return -1;
 
-	/* 2. Generate hash subkey H = AES_K(0^128) */
-	os_memset(H, 0, sizeof(H));
-	aes_encrypt(aes, H, H);
-	wpa_hexdump_key(MSG_EXCESSIVE, "Hash subkey H for GHASH", H, sizeof(H));
-
-	if (iv_len == 12) {
-		/* 3. Prepare block J_0 = IV || 0^31 || 1 [len(IV) = 96] */
-		os_memcpy(J0, iv, iv_len);
-		os_memset(J0 + iv_len, 0, AES_BLOCK_SIZE - iv_len);
-		J0[AES_BLOCK_SIZE - 1] = 0x01;
-	} else {
-		/*
-		 * s = 128 * ceil(len(IV)/128) - len(IV)
-		 * J_0 = GHASH_H(IV || 0^(s+64) || [len(IV)]_64)
-		 */
-		ghash_start(J0);
-		ghash(H, iv, iv_len, J0);
-		WPA_PUT_BE64(len_buf, 0);
-		WPA_PUT_BE64(len_buf + 8, iv_len * 8);
-		ghash(H, len_buf, sizeof(len_buf), J0);
-	}
-
-	/* 4. C = GCTR_K(inc_32(J_0), C) */
-	os_memcpy(J0inc, J0, AES_BLOCK_SIZE);
-	inc32(J0inc);
-	aes_gctr(aes, J0inc, crypt, crypt_len, plain);
+	aes_gcm_prepare_j0(iv, iv_len, H, J0);
 
-	/*
-	 * 5. u = 128 * ceil[len(C)/128] - len(C)
-	 *    v = 128 * ceil[len(A)/128] - len(A)
-	 * 6. S = GHASH_H(A || 0^v || C || 0^u || [len(A)]64 || [len(C)]64)
-	 * (i.e., zero padded to block size A || C and lengths of each in bits)
-	 */
-	ghash_start(S);
-	ghash(H, aad, aad_len, S);
-	ghash(H, crypt, crypt_len, S);
-	WPA_PUT_BE64(len_buf, aad_len * 8);
-	WPA_PUT_BE64(len_buf + 8, crypt_len * 8);
-	ghash(H, len_buf, sizeof(len_buf), S);
+	/* P = GCTR_K(inc_32(J_0), C) */
+	aes_gcm_gctr(aes, J0, crypt, crypt_len, plain);
 
-	wpa_hexdump_key(MSG_EXCESSIVE, "S = GHASH_H(...)", S, 16);
+	aes_gcm_ghash(H, aad, aad_len, crypt, crypt_len, S);
 
-	/* 7. T' = MSB_t(GCTR_K(J_0, S)) */
+	/* T' = MSB_t(GCTR_K(J_0, S)) */
 	aes_gctr(aes, J0, S, sizeof(S), T);
 
 	aes_encrypt_deinit(aes);