Add an HKDF (RFC 5869) implementation

library/CMakeLists.txt

@@ -29,6 +29,7 @@ set(src_crypto
     error.c
     gcm.c
     havege.c
+    hkdf.c
     hmac_drbg.c
     md.c
     md2.c

library/Makefile

@@ -56,6 +56,7 @@ OBJS_CRYPTO=	aes.o		aesni.o		arc4.o		\
 		ecjpake.o	ecp.o				\
 		ecp_curves.o	entropy.o	entropy_poll.o	\
 		error.o		gcm.o		havege.o	\
+		hkdf.o						\
 		hmac_drbg.o	md.o		md2.o		\
 		md4.o		md5.o		md_wrap.o	\
 		memory_buffer_alloc.o		oid.o		\

library/error.c

@@ -101,6 +101,10 @@
 #include "mbedtls/gcm.h"
 #endif
 
+#if defined(MBEDTLS_HKDF_C)
+#include "mbedtls/hkdf.h"
+#endif
+
 #if defined(MBEDTLS_HMAC_DRBG_C)
 #include "mbedtls/hmac_drbg.h"
 #endif
@@ -698,6 +702,11 @@ void mbedtls_strerror( int ret, char *buf, size_t buflen )
         mbedtls_snprintf( buf, buflen, "GCM - Bad input parameters to function" );
 #endif /* MBEDTLS_GCM_C */
 
+#if defined(MBEDTLS_HKDF_C)
+    if( use_ret == -(MBEDTLS_ERR_HKDF_BAD_INPUT_DATA) )
+        mbedtls_snprintf( buf, buflen, "HKDF - Bad input parameters to function" );
+#endif /* MBEDTLS_HKDF_C */
+
 #if defined(MBEDTLS_HMAC_DRBG_C)
     if( use_ret == -(MBEDTLS_ERR_HMAC_DRBG_REQUEST_TOO_BIG) )
         mbedtls_snprintf( buf, buflen, "HMAC_DRBG - Too many random requested in single call" );

library/hkdf.c

@@ -0,0 +1,180 @@
+/*
+ *  HKDF implementation -- RFC 5869
+ *
+ *  Copyright (C) 2016-2018, ARM Limited, All Rights Reserved
+ *  SPDX-License-Identifier: Apache-2.0
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License"); you may
+ *  not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *  http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ *
+ *  This file is part of mbed TLS (https://tls.mbed.org)
+ */
+#if !defined(MBEDTLS_CONFIG_FILE)
+#include "mbedtls/config.h"
+#else
+#include MBEDTLS_CONFIG_FILE
+#endif
+
+#if defined(MBEDTLS_HKDF_C)
+
+#include <string.h>
+#include "mbedtls/hkdf.h"
+#include "mbedtls/platform_util.h"
+
+int mbedtls_hkdf( const mbedtls_md_info_t *md, const unsigned char *salt,
+                  size_t salt_len, const unsigned char *ikm, size_t ikm_len,
+                  const unsigned char *info, size_t info_len,
+                  unsigned char *okm, size_t okm_len )
+{
+    int ret;
+    unsigned char prk[MBEDTLS_MD_MAX_SIZE];
+
+    ret = mbedtls_hkdf_extract( md, salt, salt_len, ikm, ikm_len, prk );
+
+    if( ret == 0 )
+    {
+        ret = mbedtls_hkdf_expand( md, prk, mbedtls_md_get_size( md ),
+                                   info, info_len, okm, okm_len );
+    }
+
+    mbedtls_platform_zeroize( prk, sizeof( prk ) );
+
+    return( ret );
+}
+
+int mbedtls_hkdf_extract( const mbedtls_md_info_t *md,
+                          const unsigned char *salt, size_t salt_len,
+                          const unsigned char *ikm, size_t ikm_len,
+                          unsigned char *prk )
+{
+    unsigned char null_salt[MBEDTLS_MD_MAX_SIZE] = { '\0' };
+
+    if( salt == NULL )
+    {
+        size_t hash_len;
+
+        hash_len = mbedtls_md_get_size( md );
+
+        if( hash_len == 0 )
+        {
+            return MBEDTLS_ERR_HKDF_BAD_INPUT_DATA;
+        }
+
+        salt = null_salt;
+        salt_len = hash_len;
+    }
+
+    return( mbedtls_md_hmac( md, salt, salt_len, ikm, ikm_len, prk ) );
+}
+
+int mbedtls_hkdf_expand( const mbedtls_md_info_t *md, const unsigned char *prk,
+                         size_t prk_len, const unsigned char *info,
+                         size_t info_len, unsigned char *okm, size_t okm_len )
+{
+    size_t hash_len;
+    size_t where = 0;
+    size_t n;
+    size_t t_len = 0;
+    size_t i;
+    int ret = 0;
+    mbedtls_md_context_t ctx;
+    unsigned char t[MBEDTLS_MD_MAX_SIZE];
+
+    if( okm == NULL )
+    {
+        return( MBEDTLS_ERR_HKDF_BAD_INPUT_DATA );
+    }
+
+    hash_len = mbedtls_md_get_size( md );
+
+    if( prk_len < hash_len || hash_len == 0 )
+    {
+        return( MBEDTLS_ERR_HKDF_BAD_INPUT_DATA );
+    }
+
+    if( info == NULL )
+    {
+        info = (const unsigned char *) "";
+        info_len = 0;
+    }
+
+    n = okm_len / hash_len;
+
+    if( (okm_len % hash_len) != 0 )
+    {
+        n++;
+    }
+
+    if( n > 255 )
+    {
+        return( MBEDTLS_ERR_HKDF_BAD_INPUT_DATA );
+    }
+
+    mbedtls_md_init( &ctx );
+
+    if( (ret = mbedtls_md_setup( &ctx, md, 1) ) != 0 )
+    {
+        goto exit;
+    }
+
+    /* RFC 5869 Section 2.3. */
+    for( i = 1; i <= n; i++ )
+    {
+        size_t num_to_copy;
+        unsigned char c = i & 0xff;
+
+        ret = mbedtls_md_hmac_starts( &ctx, prk, prk_len );
+        if( ret != 0 )
+        {
+            goto exit;
+        }
+
+        ret = mbedtls_md_hmac_update( &ctx, t, t_len );
+        if( ret != 0 )
+        {
+            goto exit;
+        }
+
+        ret = mbedtls_md_hmac_update( &ctx, info, info_len );
+        if( ret != 0 )
+        {
+            goto exit;
+        }
+
+        /* The constant concatenated to the end of each t(n) is a single octet.
+         * */
+        ret = mbedtls_md_hmac_update( &ctx, &c, 1 );
+        if( ret != 0 )
+        {
+            goto exit;
+        }
+
+        ret = mbedtls_md_hmac_finish( &ctx, t );
+        if( ret != 0 )
+        {
+            goto exit;
+        }
+
+        num_to_copy = i != n ? hash_len : okm_len - where;
+        memcpy( okm + where, t, num_to_copy );
+        where += hash_len;
+        t_len = hash_len;
+    }
+
+exit:
+    mbedtls_md_free( &ctx );
+    mbedtls_platform_zeroize( t, sizeof( t ) );
+
+    return( ret );
+}
+
+#endif /* MBEDTLS_HKDF_C */

library/version_features.c

@@ -579,6 +579,9 @@ static const char *features[] = {
 #if defined(MBEDTLS_HAVEGE_C)
     "MBEDTLS_HAVEGE_C",
 #endif /* MBEDTLS_HAVEGE_C */
+#if defined(MBEDTLS_HKDF_C)
+    "MBEDTLS_HKDF_C",
+#endif /* MBEDTLS_HKDF_C */
 #if defined(MBEDTLS_HMAC_DRBG_C)
     "MBEDTLS_HMAC_DRBG_C",
 #endif /* MBEDTLS_HMAC_DRBG_C */