hmac_done.c

/* LibTomCrypt, modular cryptographic library -- Tom St Denis */
/* SPDX-License-Identifier: Unlicense */
#include "tomcrypt_private.h"

/**
  @file hmac_done.c
  HMAC support, terminate stream, Tom St Denis/Dobes Vandermeer
*/

#ifdef LTC_HMAC

#define LTC_HMAC_BLOCKSIZE hash_descriptor[hash].blocksize

/**
   Terminate an HMAC session
   @param hmac    The HMAC state
   @param out     [out] The destination of the HMAC authentication tag
   @param outlen  [in/out]  The max size and resulting size of the HMAC authentication tag
   @return CRYPT_OK if successful
*/
int hmac_done(hmac_state *hmac, unsigned char *out, unsigned long *outlen)
{
    unsigned char *buf, *isha;
    unsigned long hashsize, i;
    int hash, err;

    LTC_ARGCHK(hmac  != NULL);
    LTC_ARGCHK(out   != NULL);

    /* test hash */
    hash = hmac->hash;
    if((err = hash_is_valid(hash)) != CRYPT_OK) {
        return err;
    }

    /* get the hash message digest size */
    hashsize = hash_descriptor[hash].hashsize;

    /* allocate buffers */
    buf  = XMALLOC(LTC_HMAC_BLOCKSIZE);
    isha = XMALLOC(hashsize);
    if (buf == NULL || isha == NULL) {
       if (buf != NULL) {
          XFREE(buf);
       }
       if (isha != NULL) {
          XFREE(isha);
       }
       return CRYPT_MEM;
    }

    /* Get the hash of the first HMAC vector plus the data */
    if ((err = hash_descriptor[hash].done(&hmac->md, isha)) != CRYPT_OK) {
       goto LBL_ERR;
    }

    /* Create the second HMAC vector vector for step (3) */
    for(i=0; i < LTC_HMAC_BLOCKSIZE; i++) {
        buf[i] = hmac->key[i] ^ 0x5C;
    }

    /* Now calculate the "outer" hash for step (5), (6), and (7) */
    if ((err = hash_descriptor[hash].init(&hmac->md)) != CRYPT_OK) {
       goto LBL_ERR;
    }
    if ((err = hash_descriptor[hash].process(&hmac->md, buf, LTC_HMAC_BLOCKSIZE)) != CRYPT_OK) {
       goto LBL_ERR;
    }
    if ((err = hash_descriptor[hash].process(&hmac->md, isha, hashsize)) != CRYPT_OK) {
       goto LBL_ERR;
    }
    if ((err = hash_descriptor[hash].done(&hmac->md, buf)) != CRYPT_OK) {
       goto LBL_ERR;
    }

    /* copy to output  */
    for (i = 0; i < hashsize && i < *outlen; i++) {
        out[i] = buf[i];
    }
    *outlen = i;

    err = CRYPT_OK;
LBL_ERR:
#ifdef LTC_CLEAN_STACK
    zeromem(isha, hashsize);
    zeromem(buf,  hashsize);
    zeromem(hmac, sizeof(*hmac));
#endif

    XFREE(isha);
    XFREE(buf);

    return err;
}

#endif