File content as of revision 49:6bb8b9a66642:

// Copyright (c) Microsoft. All rights reserved.
// Licensed under the MIT license. See LICENSE file in the project root for full license information.

/**************************** hmac.c ****************************/
/******************** See RFC 4634 for details ******************/
/*
*  Description:
*      This file implements the HMAC algorithm (Keyed-Hashing for
*      Message Authentication, RFC2104), expressed in terms of the
*      various SHA algorithms.
*/

#include "azure_c_shared_utility/sha.h"

/*
*  hmac
*
*  Description:
*      This function will compute an HMAC message digest.
*
*  Parameters:
*      whichSha: [in]
*          One of SHA1, SHA224, SHA256, SHA384, SHA512
*      key: [in]
*          The secret shared key.
*      key_len: [in]
*          The length of the secret shared key.
*      message_array: [in]
*          An array of characters representing the message.
*      length: [in]
*          The length of the message in message_array
*      digest: [out]
*          Where the digest is returned.
*          NOTE: The length of the digest is determined by
*              the value of whichSha.
*
*  Returns:
*      sha Error Code.
*
*/
int hmac(SHAversion whichSha, const unsigned char *text, int text_len,
    const unsigned char *key, int key_len,
    uint8_t digest[USHAMaxHashSize])
{
    HMACContext ctx;
    return hmacReset(&ctx, whichSha, key, key_len) ||
        hmacInput(&ctx, text, text_len) ||
        hmacResult(&ctx, digest);
}

/*
*  hmacReset
*
*  Description:
*      This function will initialize the hmacContext in preparation
*      for computing a new HMAC message digest.
*
*  Parameters:
*      context: [in/out]
*          The context to reset.
*      whichSha: [in]
*          One of SHA1, SHA224, SHA256, SHA384, SHA512
*      key: [in]
*          The secret shared key.
*      key_len: [in]
*          The length of the secret shared key.
*
*  Returns:
*      sha Error Code.
*
*/
int hmacReset(HMACContext *ctx, enum SHAversion whichSha,
    const unsigned char *key, int key_len)
{
    int i, blocksize, hashsize;

    /* inner padding - key XORd with ipad */
    unsigned char k_ipad[USHA_Max_Message_Block_Size];

    /* temporary buffer when keylen > blocksize */
    unsigned char tempkey[USHAMaxHashSize];

    if (!ctx) return shaNull;

    blocksize = ctx->blockSize = USHABlockSize(whichSha);
    hashsize = ctx->hashSize = USHAHashSize(whichSha);

    ctx->whichSha = whichSha;

    /*
    * If key is longer than the hash blocksize,
    * reset it to key = HASH(key).
    */
    if (key_len > blocksize) {
        USHAContext tctx;
        int err = USHAReset(&tctx, whichSha) ||
            USHAInput(&tctx, key, key_len) ||
            USHAResult(&tctx, tempkey);
        if (err != shaSuccess) return err;

        key = tempkey;
        key_len = hashsize;
    }

    /*
    * The HMAC transform looks like:
    *
    * SHA(K XOR opad, SHA(K XOR ipad, text))
    *
    * where K is an n byte key.
    * ipad is the byte 0x36 repeated blocksize times
    * opad is the byte 0x5c repeated blocksize times
    * and text is the data being protected.
    */

    /* store key into the pads, XOR'd with ipad and opad values */
    for (i = 0; i < key_len; i++) {
        k_ipad[i] = key[i] ^ 0x36;
        ctx->k_opad[i] = key[i] ^ 0x5c;
    }
    /* remaining pad bytes are '\0' XOR'd with ipad and opad values */
    for (; i < blocksize; i++) {
        k_ipad[i] = 0x36;
        ctx->k_opad[i] = 0x5c;
    }

    /* perform inner hash */
    /* init context for 1st pass */
    return USHAReset(&ctx->shaContext, whichSha) ||
        /* and start with inner pad */
        USHAInput(&ctx->shaContext, k_ipad, blocksize);
}

/*
*  hmacInput
*
*  Description:
*      This function accepts an array of octets as the next portion
*      of the message.
*
*  Parameters:
*      context: [in/out]
*          The HMAC context to update
*      message_array: [in]
*          An array of characters representing the next portion of
*          the message.
*      length: [in]
*          The length of the message in message_array
*
*  Returns:
*      sha Error Code.
*
*/
int hmacInput(HMACContext *ctx, const unsigned char *text,
    int text_len)
{
    if (!ctx) return shaNull;
    /* then text of datagram */
    return USHAInput(&ctx->shaContext, text, text_len);
}

/*
* HMACFinalBits
*
* Description:
*   This function will add in any final bits of the message.
*
* Parameters:
*   context: [in/out]
*     The HMAC context to update
*   message_bits: [in]
*     The final bits of the message, in the upper portion of the
*     byte. (Use 0b###00000 instead of 0b00000### to input the
*     three bits ###.)
*   length: [in]
*     The number of bits in message_bits, between 1 and 7.
*
* Returns:
*   sha Error Code.
*/
int hmacFinalBits(HMACContext *ctx,
    const uint8_t bits,
    unsigned int bitcount)
{
    if (!ctx) return shaNull;
    /* then final bits of datagram */
    return USHAFinalBits(&ctx->shaContext, bits, bitcount);
}

/*
* HMACResult
*
* Description:
*   This function will return the N-byte message digest into the
*   Message_Digest array provided by the caller.
*   NOTE: The first octet of hash is stored in the 0th element,
*      the last octet of hash in the Nth element.
*
* Parameters:
*   context: [in/out]
*     The context to use to calculate the HMAC hash.
*   digest: [out]
*     Where the digest is returned.
*   NOTE 2: The length of the hash is determined by the value of
*      whichSha that was passed to hmacReset().
*
* Returns:
*   sha Error Code.
*
*/
int hmacResult(HMACContext *ctx, uint8_t *digest)
{
    if (!ctx) return shaNull;

    /* finish up 1st pass */
    /* (Use digest here as a temporary buffer.) */
    return USHAResult(&ctx->shaContext, digest) ||

        /* perform outer SHA */
        /* init context for 2nd pass */
        USHAReset(&ctx->shaContext, (SHAversion)ctx->whichSha) ||

        /* start with outer pad */
        USHAInput(&ctx->shaContext, ctx->k_opad, ctx->blockSize) ||

        /* then results of 1st hash */
        USHAInput(&ctx->shaContext, digest, ctx->hashSize) ||

        /* finish up 2nd pass */
        USHAResult(&ctx->shaContext, digest);
}