/* * HKDF implementation -- RFC 5869 * * Copyright The Mbed TLS Contributors * 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. */ #include "common.h" #if defined(MBEDTLS_HKDF_C) #include <string.h> #include "mbedtls/hkdf.h" #include "mbedtls/platform_util.h" #include "mbedtls/error.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 = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED; 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; if( salt_len != 0 ) { return MBEDTLS_ERR_HKDF_BAD_INPUT_DATA; } 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++; } /* * Per RFC 5869 Section 2.3, okm_len must not exceed * 255 times the hash length */ 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; } memset( t, 0, hash_len ); /* * Compute T = T(1) | T(2) | T(3) | ... | T(N) * Where T(N) is defined in 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 */