Mercurial > dropbear
annotate libtomcrypt/src/encauth/ocb3/ocb3_decrypt.c @ 1749:32307118bc26
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author | Matt Johnston <matt@ucc.asn.au> |
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date | Mon, 19 Oct 2020 23:38:11 +0800 |
parents | 6dba84798cd5 |
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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 |
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10 /** |
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11 @file ocb3_decrypt.c |
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12 OCB implementation, decrypt data, by Tom St Denis |
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13 */ |
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14 #include "tomcrypt.h" |
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15 |
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16 #ifdef LTC_OCB3_MODE |
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17 |
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18 /** |
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19 Decrypt blocks of ciphertext with OCB |
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20 @param ocb The OCB state |
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21 @param ct The ciphertext (length multiple of the block size of the block cipher) |
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22 @param ctlen The length of the input (octets) |
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23 @param pt [out] The plaintext (length of ct) |
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24 @return CRYPT_OK if successful |
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25 */ |
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26 int ocb3_decrypt(ocb3_state *ocb, const unsigned char *ct, unsigned long ctlen, unsigned char *pt) |
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27 { |
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28 unsigned char tmp[MAXBLOCKSIZE]; |
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29 int err, i, full_blocks; |
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30 unsigned char *pt_b, *ct_b; |
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31 |
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32 LTC_ARGCHK(ocb != NULL); |
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33 if (ctlen == 0) return CRYPT_OK; /* no data, nothing to do */ |
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34 LTC_ARGCHK(ct != NULL); |
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35 LTC_ARGCHK(pt != NULL); |
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36 |
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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 if (ocb->block_len != cipher_descriptor[ocb->cipher].block_length) { |
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41 return CRYPT_INVALID_ARG; |
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42 } |
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43 |
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44 if (ctlen % ocb->block_len) { /* ctlen has to bu multiple of block_len */ |
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45 return CRYPT_INVALID_ARG; |
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46 } |
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47 |
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48 full_blocks = ctlen/ocb->block_len; |
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49 for(i=0; i<full_blocks; i++) { |
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50 pt_b = (unsigned char *)pt+i*ocb->block_len; |
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51 ct_b = (unsigned char *)ct+i*ocb->block_len; |
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52 |
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53 /* ocb->Offset_current[] = ocb->Offset_current[] ^ Offset_{ntz(block_index)} */ |
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54 ocb3_int_xor_blocks(ocb->Offset_current, ocb->Offset_current, ocb->L_[ocb3_int_ntz(ocb->block_index)], ocb->block_len); |
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55 |
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56 /* tmp[] = ct[] XOR ocb->Offset_current[] */ |
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57 ocb3_int_xor_blocks(tmp, ct_b, ocb->Offset_current, ocb->block_len); |
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58 |
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59 /* decrypt */ |
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60 if ((err = cipher_descriptor[ocb->cipher].ecb_decrypt(tmp, tmp, &ocb->key)) != CRYPT_OK) { |
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61 goto LBL_ERR; |
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62 } |
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63 |
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64 /* pt[] = tmp[] XOR ocb->Offset_current[] */ |
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65 ocb3_int_xor_blocks(pt_b, tmp, ocb->Offset_current, ocb->block_len); |
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66 |
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67 /* ocb->checksum[] = ocb->checksum[] XOR pt[] */ |
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68 ocb3_int_xor_blocks(ocb->checksum, ocb->checksum, pt_b, ocb->block_len); |
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69 |
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70 ocb->block_index++; |
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71 } |
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72 |
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73 err = CRYPT_OK; |
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74 |
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75 LBL_ERR: |
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76 #ifdef LTC_CLEAN_STACK |
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77 zeromem(tmp, sizeof(tmp)); |
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78 #endif |
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79 return err; |
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80 } |
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81 |
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82 #endif |
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83 |
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84 /* ref: $Format:%D$ */ |
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85 /* git commit: $Format:%H$ */ |
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86 /* commit time: $Format:%ai$ */ |