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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 
     12 /**
     13    @file eax_done.c
     14    EAX implementation, terminate session, by Tom St Denis
     15 */
     16 #include "tomcrypt.h"
     17 
     18 #ifdef EAX_MODE
     19 
     20 /**
     21    Terminate an EAX session and get the tag.
     22    @param eax       The EAX state
     23    @param tag       [out] The destination of the authentication tag
     24    @param taglen    [in/out] The max length and resulting length of the authentication tag
     25    @return CRYPT_OK if successful
     26 */
     27 int eax_done(eax_state *eax, unsigned char *tag, unsigned long *taglen)
     28 {
     29    int           err;
     30    unsigned char *headermac, *ctmac;
     31    unsigned long x, len;
     32 
     33    LTC_ARGCHK(eax    != NULL);
     34    LTC_ARGCHK(tag    != NULL);
     35    LTC_ARGCHK(taglen != NULL);
     36 
     37    /* allocate ram */
     38    headermac = XMALLOC(MAXBLOCKSIZE);
     39    ctmac     = XMALLOC(MAXBLOCKSIZE);
     40 
     41    if (headermac == NULL || ctmac == NULL) {
     42       if (headermac != NULL) {
     43          XFREE(headermac);
     44       }
     45       if (ctmac != NULL) {
     46          XFREE(ctmac);
     47       }
     48       return CRYPT_MEM;
     49    }
     50 
     51    /* finish ctomac */
     52    len = MAXBLOCKSIZE;
     53    if ((err = omac_done(&eax->ctomac, ctmac, &len)) != CRYPT_OK) {
     54       goto LBL_ERR;
     55    }
     56 
     57    /* finish headeromac */
     58 
     59    /* note we specifically don't reset len so the two lens are minimal */
     60 
     61    if ((err = omac_done(&eax->headeromac, headermac, &len)) != CRYPT_OK) {
     62       goto LBL_ERR;
     63    }
     64 
     65    /* terminate the CTR chain */
     66    if ((err = ctr_done(&eax->ctr)) != CRYPT_OK) {
     67       goto LBL_ERR;
     68    }
     69 
     70    /* compute N xor H xor C */
     71    for (x = 0; x < len && x < *taglen; x++) {
     72        tag[x] = eax->N[x] ^ headermac[x] ^ ctmac[x];
     73    }
     74    *taglen = x;
     75 
     76    err = CRYPT_OK;
     77 LBL_ERR:
     78 #ifdef LTC_CLEAN_STACK
     79    zeromem(ctmac,     MAXBLOCKSIZE);
     80    zeromem(headermac, MAXBLOCKSIZE);
     81    zeromem(eax,       sizeof(*eax));
     82 #endif
     83 
     84    XFREE(ctmac);
     85    XFREE(headermac);
     86 
     87    return err;
     88 }
     89 
     90 #endif
     91 
     92 /* $Source: /cvs/libtom/libtomcrypt/src/encauth/eax/eax_done.c,v $ */
     93 /* $Revision: 1.5 $ */
     94 /* $Date: 2006/03/31 14:15:35 $ */
     95