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      1 /* LibTomCrypt, modular cryptographic library -- Tom St Denis
      2  *
      3  * LibTomCrypt is a library that provides various cryptographic
      4  * algorithms in a highly modular and flexible manner.
      5  *
      6  * The library is free for all purposes without any express
      7  * guarantee it works.
      8  *
      9  * Tom St Denis, tomstdenis (at) gmail.com, http://libtomcrypt.com
     10  */
     11 #include "tomcrypt.h"
     12 
     13 /**
     14   @file hmac_done.c
     15   HMAC support, terminate stream, Tom St Denis/Dobes Vandermeer
     16 */
     17 
     18 #ifdef LTC_HMAC
     19 
     20 #define HMAC_BLOCKSIZE hash_descriptor[hash].blocksize
     21 
     22 /**
     23    Terminate an HMAC session
     24    @param hmac    The HMAC state
     25    @param out     [out] The destination of the HMAC authentication tag
     26    @param outlen  [in/out]  The max size and resulting size of the HMAC authentication tag
     27    @return CRYPT_OK if successful
     28 */
     29 int hmac_done(hmac_state *hmac, unsigned char *out, unsigned long *outlen)
     30 {
     31     unsigned char *buf, *isha;
     32     unsigned long hashsize, i;
     33     int hash, err;
     34 
     35     LTC_ARGCHK(hmac  != NULL);
     36     LTC_ARGCHK(out   != NULL);
     37 
     38     /* test hash */
     39     hash = hmac->hash;
     40     if((err = hash_is_valid(hash)) != CRYPT_OK) {
     41         return err;
     42     }
     43 
     44     /* get the hash message digest size */
     45     hashsize = hash_descriptor[hash].hashsize;
     46 
     47     /* allocate buffers */
     48     buf  = XMALLOC(HMAC_BLOCKSIZE);
     49     isha = XMALLOC(hashsize);
     50     if (buf == NULL || isha == NULL) {
     51        if (buf != NULL) {
     52           XFREE(buf);
     53        }
     54        if (isha != NULL) {
     55           XFREE(isha);
     56        }
     57        return CRYPT_MEM;
     58     }
     59 
     60     /* Get the hash of the first HMAC vector plus the data */
     61     if ((err = hash_descriptor[hash].done(&hmac->md, isha)) != CRYPT_OK) {
     62        goto LBL_ERR;
     63     }
     64 
     65     /* Create the second HMAC vector vector for step (3) */
     66     for(i=0; i < HMAC_BLOCKSIZE; i++) {
     67         buf[i] = hmac->key[i] ^ 0x5C;
     68     }
     69 
     70     /* Now calculate the "outer" hash for step (5), (6), and (7) */
     71     if ((err = hash_descriptor[hash].init(&hmac->md)) != CRYPT_OK) {
     72        goto LBL_ERR;
     73     }
     74     if ((err = hash_descriptor[hash].process(&hmac->md, buf, HMAC_BLOCKSIZE)) != CRYPT_OK) {
     75        goto LBL_ERR;
     76     }
     77     if ((err = hash_descriptor[hash].process(&hmac->md, isha, hashsize)) != CRYPT_OK) {
     78        goto LBL_ERR;
     79     }
     80     if ((err = hash_descriptor[hash].done(&hmac->md, buf)) != CRYPT_OK) {
     81        goto LBL_ERR;
     82     }
     83 
     84     /* copy to output  */
     85     for (i = 0; i < hashsize && i < *outlen; i++) {
     86         out[i] = buf[i];
     87     }
     88     *outlen = i;
     89 
     90     err = CRYPT_OK;
     91 LBL_ERR:
     92     XFREE(hmac->key);
     93 #ifdef LTC_CLEAN_STACK
     94     zeromem(isha, hashsize);
     95     zeromem(buf,  hashsize);
     96     zeromem(hmac, sizeof(*hmac));
     97 #endif
     98 
     99     XFREE(isha);
    100     XFREE(buf);
    101 
    102     return err;
    103 }
    104 
    105 #endif
    106 
    107 /* $Source: /cvs/libtom/libtomcrypt/src/mac/hmac/hmac_done.c,v $ */
    108 /* $Revision: 1.5 $ */
    109 /* $Date: 2006/11/03 00:39:49 $ */
    110