Add support for CMAC (RFC 4493).

The interface for this is very similar to upstream, but the code is
quite different.

Support for “resuming” (i.e. calling |CMAC_Final| and then computing the
CMAC for an extension of the message) has been dropped. Also, calling
|CMAC_Init| with magic argument to reset it has been replaced with
|CMAC_Reset|.

Lastly, a one-shot function has been added because it can save an
allocation and that's what most callers actually appear to want to do.

Change-Id: I9345220218bdb16ebe6ca356928d7c6f055d83f6
Reviewed-on: https://boringssl-review.googlesource.com/4630
Reviewed-by: David Benjamin <davidben@chromium.org>
Reviewed-by: Adam Langley <agl@google.com>

1 files changed, 76 insertions, 0 deletions

diff --git a/include/openssl/cmac.h b/include/openssl/cmac.h
new file mode 100644
index 00000000..183f41bc
--- /dev/null
+++ b/include/openssl/cmac.h
@@ -0,0 +1,76 @@
+/* Copyright (c) 2015, Google Inc.
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
+ * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
+ * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
+ * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
+
+#ifndef OPENSSL_HEADER_CMAC_H
+#define OPENSSL_HEADER_CMAC_H
+
+#include <openssl/base.h>
+
+#if defined(__cplusplus)
+extern "C" {
+#endif
+
+
+/* CMAC.
+ *
+ * CMAC is a MAC based on AES-CBC and defined in
+ * https://tools.ietf.org/html/rfc4493#section-2.3. */
+
+
+/* One-shot functions. */
+
+/* AES_CMAC calculates the 16-byte, CMAC authenticator of |in_len| bytes of
+ * |in| and writes it to |out|. The |key_len| may be 16 or 32 bytes to select
+ * between AES-128 and AES-256. It returns one on success or zero on error. */
+OPENSSL_EXPORT int AES_CMAC(uint8_t out[16], const uint8_t *key, size_t key_len,
+                            const uint8_t *in, size_t in_len);
+
+
+/* Incremental interface. */
+
+/* CMAC_CTX_new allocates a fresh |CMAC_CTX| and returns it, or NULL on
+ * error. */
+OPENSSL_EXPORT CMAC_CTX *CMAC_CTX_new(void);
+
+/* CMAC_CTX_free frees a |CMAC_CTX|. */
+OPENSSL_EXPORT void CMAC_CTX_free(CMAC_CTX *ctx);
+
+/* CMAC_Init configures |ctx| to use the given |key| and |cipher|. The CMAC RFC
+ * only specifies the use of AES-128 thus |key_len| should be 16 and |cipher|
+ * should be |EVP_aes_128_cbc()|. However, this implementation also supports
+ * AES-256 by setting |key_len| to 32 and |cipher| to |EVP_aes_256_cbc()|. The
+ * |engine| argument is ignored.
+ *
+ * It returns one on success or zero on error. */
+OPENSSL_EXPORT int CMAC_Init(CMAC_CTX *ctx, const void *key, size_t key_len,
+                             const EVP_CIPHER *cipher, ENGINE *engine);
+
+
+/* CMAC_Reset resets |ctx| so that a fresh message can be authenticated. */
+OPENSSL_EXPORT int CMAC_Reset(CMAC_CTX *ctx);
+
+/* CMAC_Update processes |in_len| bytes of message from |in|. It returns one on
+ * success or zero on error. */
+OPENSSL_EXPORT int CMAC_Update(CMAC_CTX *ctx, const uint8_t *in, size_t in_len);
+
+/* CMAC_Final sets |*out_len| to 16 and, if |out| is not NULL, writes 16 bytes
+ * of authenticator to it. It returns one on success or zero on error. */
+OPENSSL_EXPORT int CMAC_Final(CMAC_CTX *ctx, uint8_t *out, size_t *out_len);
+
+
+#if defined(__cplusplus)
+}  /* extern C */
+#endif
+
+#endif  /* OPENSSL_HEADER_CBC_H */