Mercurial > dropbear
annotate libtomcrypt/src/encauth/ocb/ocb_decrypt.c @ 469:8c2d2edadf2a
Update to debian 0.50-4 diff
author | Matt Johnston <matt@ucc.asn.au> |
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date | Thu, 27 Mar 2008 10:19:28 +0000 |
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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.com |
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10 */ |
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11 |
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12 /** |
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13 @file ocb_decrypt.c |
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14 OCB implementation, decrypt data, by Tom St Denis |
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15 */ |
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16 #include "tomcrypt.h" |
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17 |
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18 #ifdef OCB_MODE |
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19 |
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20 /** |
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21 Decrypt a block with OCB. |
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22 @param ocb The OCB state |
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23 @param ct The ciphertext (length of the block size of the block cipher) |
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24 @param pt [out] The plaintext (length of ct) |
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25 @return CRYPT_OK if successful |
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26 */ |
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27 int ocb_decrypt(ocb_state *ocb, const unsigned char *ct, unsigned char *pt) |
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28 { |
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29 unsigned char Z[MAXBLOCKSIZE], tmp[MAXBLOCKSIZE]; |
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30 int err, x; |
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31 |
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32 LTC_ARGCHK(ocb != NULL); |
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33 LTC_ARGCHK(pt != NULL); |
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34 LTC_ARGCHK(ct != NULL); |
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35 |
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36 /* check if valid cipher */ |
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37 if ((err = cipher_is_valid(ocb->cipher)) != CRYPT_OK) { |
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38 return err; |
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39 } |
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40 LTC_ARGCHK(cipher_descriptor[ocb->cipher].ecb_decrypt != NULL); |
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41 |
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42 /* check length */ |
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43 if (ocb->block_len != cipher_descriptor[ocb->cipher].block_length) { |
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44 return CRYPT_INVALID_ARG; |
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45 } |
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46 |
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47 /* Get Z[i] value */ |
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48 ocb_shift_xor(ocb, Z); |
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49 |
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50 /* xor ct in, encrypt, xor Z out */ |
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51 for (x = 0; x < ocb->block_len; x++) { |
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52 tmp[x] = ct[x] ^ Z[x]; |
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53 } |
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54 if ((err = cipher_descriptor[ocb->cipher].ecb_decrypt(tmp, pt, &ocb->key)) != CRYPT_OK) { |
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55 return err; |
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56 } |
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57 for (x = 0; x < ocb->block_len; x++) { |
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58 pt[x] ^= Z[x]; |
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59 } |
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60 |
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61 /* compute checksum */ |
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62 for (x = 0; x < ocb->block_len; x++) { |
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63 ocb->checksum[x] ^= pt[x]; |
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64 } |
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65 |
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66 |
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67 #ifdef LTC_CLEAN_STACK |
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68 zeromem(Z, sizeof(Z)); |
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69 zeromem(tmp, sizeof(tmp)); |
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70 #endif |
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71 return CRYPT_OK; |
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72 } |
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73 |
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74 #endif |
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75 |
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76 |
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77 /* $Source: /cvs/libtom/libtomcrypt/src/encauth/ocb/ocb_decrypt.c,v $ */ |
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78 /* $Revision: 1.5 $ */ |
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79 /* $Date: 2006/03/31 14:15:35 $ */ |