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annotate cbc_decrypt.c @ 0:d7da3b1e1540 libtomcrypt

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put back the 0.95 makefile which was inadvertently merged over
author Matt Johnston <matt@ucc.asn.au>
date Mon, 31 May 2004 18:21:40 +0000
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children 6362d3854bb4
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d7da3b1e1540 put back the 0.95 makefile which was inadvertently merged over
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1 /* LibTomCrypt, modular cryptographic library -- Tom St Denis
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2 *
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3 * LibTomCrypt is a library that provides various cryptographic
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4 * algorithms in a highly modular and flexible manner.
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5 *
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6 * The library is free for all purposes without any express
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7 * guarantee it works.
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8 *
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9 * Tom St Denis, [email protected], http://libtomcrypt.org
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10 */
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11 #include "mycrypt.h"
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12
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13 #ifdef CBC
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14
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15 int cbc_decrypt(const unsigned char *ct, unsigned char *pt, symmetric_CBC *cbc)
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16 {
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17 int x, err;
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18 unsigned char tmp[MAXBLOCKSIZE], tmp2[MAXBLOCKSIZE];
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19
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20 _ARGCHK(pt != NULL);
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21 _ARGCHK(ct != NULL);
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22 _ARGCHK(cbc != NULL);
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23
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24 /* decrypt the block from ct into tmp */
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25 if ((err = cipher_is_valid(cbc->cipher)) != CRYPT_OK) {
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26 return err;
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27 }
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28 cipher_descriptor[cbc->cipher].ecb_decrypt(ct, tmp, &cbc->key);
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29
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30 /* is blocklen valid? */
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31 if (cbc->blocklen < 0 || cbc->blocklen > (int)sizeof(cbc->IV)) {
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32 return CRYPT_INVALID_ARG;
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33 }
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34
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35 /* xor IV against the plaintext of the previous step */
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36 for (x = 0; x < cbc->blocklen; x++) {
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37 /* copy CT in case ct == pt */
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38 tmp2[x] = ct[x];
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39
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40 /* actually decrypt the byte */
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41 pt[x] = tmp[x] ^ cbc->IV[x];
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42 }
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43
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44 /* replace IV with this current ciphertext */
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45 for (x = 0; x < cbc->blocklen; x++) {
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46 cbc->IV[x] = tmp2[x];
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47 }
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48 #ifdef CLEAN_STACK
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49 zeromem(tmp, sizeof(tmp));
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50 zeromem(tmp2, sizeof(tmp2));
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51 #endif
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52 return CRYPT_OK;
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53 }
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54
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55 #endif
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56