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annotate src/modes/cbc/cbc_decrypt.c @ 191:1c15b283127b libtomcrypt-orig

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Import of libtomcrypt 1.02 with manual path rename rearrangement etc
author Matt Johnston <matt@ucc.asn.au>
date Fri, 06 May 2005 13:23:02 +0000
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children 39d5d58461d6
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191
1c15b283127b Import of libtomcrypt 1.02 with manual path rename rearrangement etc
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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 "tomcrypt.h"
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12
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13 /**
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14 @file cbc_decrypt.c
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15 CBC implementation, encrypt block, Tom St Denis
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16 */
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17
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18
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19 #ifdef CBC
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20
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21 /**
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22 CBC decrypt
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23 @param ct Ciphertext
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24 @param pt [out] Plaintext
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25 @param len The number of bytes to process (must be multiple of block length)
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26 @param cbc CBC state
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27 @return CRYPT_OK if successful
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28 */
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29 int cbc_decrypt(const unsigned char *ct, unsigned char *pt, unsigned long len, symmetric_CBC *cbc)
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30 {
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31 int x, err;
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32 unsigned char tmp[16];
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33 #ifdef LTC_FAST
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34 LTC_FAST_TYPE tmpy;
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35 #else
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36 unsigned char tmpy;
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37 #endif
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38
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39 LTC_ARGCHK(pt != NULL);
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40 LTC_ARGCHK(ct != NULL);
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41 LTC_ARGCHK(cbc != NULL);
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42
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43 if ((err = cipher_is_valid(cbc->cipher)) != CRYPT_OK) {
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44 return err;
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45 }
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46
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47 /* is blocklen valid? */
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48 if (cbc->blocklen < 0 || cbc->blocklen > (int)sizeof(cbc->IV)) {
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49 return CRYPT_INVALID_ARG;
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50 }
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51
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52 if (len % cbc->blocklen) {
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53 return CRYPT_INVALID_ARG;
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54 }
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55 #ifdef LTC_FAST
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56 if (len % sizeof(LTC_FAST_TYPE)) {
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57 return CRYPT_INVALID_ARG;
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58 }
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59 #endif
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60
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61 if (cipher_descriptor[cbc->cipher].accel_cbc_decrypt != NULL) {
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62 cipher_descriptor[cbc->cipher].accel_cbc_decrypt(ct, pt, len / cbc->blocklen, cbc->IV, &cbc->key);
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63 } else {
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64 while (len) {
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65 /* decrypt */
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66 cipher_descriptor[cbc->cipher].ecb_decrypt(ct, tmp, &cbc->key);
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67
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68 /* xor IV against plaintext */
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69 #if defined(LTC_FAST)
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70 for (x = 0; x < cbc->blocklen; x += sizeof(LTC_FAST_TYPE)) {
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71 tmpy = *((LTC_FAST_TYPE*)((unsigned char *)cbc->IV + x)) ^ *((LTC_FAST_TYPE*)((unsigned char *)tmp + x));
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72 *((LTC_FAST_TYPE*)((unsigned char *)cbc->IV + x)) = *((LTC_FAST_TYPE*)((unsigned char *)ct + x));
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73 *((LTC_FAST_TYPE*)((unsigned char *)pt + x)) = tmpy;
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74 }
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75 #else
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76 for (x = 0; x < cbc->blocklen; x++) {
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77 tmpy = tmp[x] ^ cbc->IV[x];
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78 cbc->IV[x] = ct[x];
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79 pt[x] = tmpy;
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80 }
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81 #endif
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82
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83 ct += cbc->blocklen;
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84 pt += cbc->blocklen;
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85 len -= cbc->blocklen;
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86 }
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87 }
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88 return CRYPT_OK;
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89 }
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90
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91 #endif