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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 |
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12 /* OCB Implementation by Tom St Denis */ |
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13 #include "mycrypt.h" |
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14 |
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15 #ifdef OCB_MODE |
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16 |
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17 int ocb_decrypt(ocb_state *ocb, const unsigned char *ct, unsigned char *pt) |
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18 { |
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19 unsigned char Z[MAXBLOCKSIZE], tmp[MAXBLOCKSIZE]; |
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20 int err, x; |
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21 |
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22 _ARGCHK(ocb != NULL); |
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23 _ARGCHK(pt != NULL); |
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24 _ARGCHK(ct != NULL); |
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25 |
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26 /* check if valid cipher */ |
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27 if ((err = cipher_is_valid(ocb->cipher)) != CRYPT_OK) { |
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28 return err; |
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29 } |
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30 _ARGCHK(cipher_descriptor[ocb->cipher].ecb_decrypt != NULL); |
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31 |
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32 /* check length */ |
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33 if (ocb->block_len != cipher_descriptor[ocb->cipher].block_length) { |
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34 return CRYPT_INVALID_ARG; |
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35 } |
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36 |
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37 /* Get Z[i] value */ |
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38 ocb_shift_xor(ocb, Z); |
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39 |
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40 /* xor ct in, encrypt, xor Z out */ |
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41 for (x = 0; x < ocb->block_len; x++) { |
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42 tmp[x] = ct[x] ^ Z[x]; |
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43 } |
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44 cipher_descriptor[ocb->cipher].ecb_decrypt(tmp, pt, &ocb->key); |
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45 for (x = 0; x < ocb->block_len; x++) { |
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46 pt[x] ^= Z[x]; |
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47 } |
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48 |
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49 /* compute checksum */ |
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50 for (x = 0; x < ocb->block_len; x++) { |
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51 ocb->checksum[x] ^= pt[x]; |
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52 } |
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53 |
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54 |
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55 #ifdef CLEAN_STACK |
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56 zeromem(Z, sizeof(Z)); |
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57 zeromem(tmp, sizeof(tmp)); |
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58 #endif |
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59 return CRYPT_OK; |
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60 } |
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61 |
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62 #endif |
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63 |
