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annotate libtomcrypt/src/encauth/ocb3/ocb3_decrypt.c @ 1766:b14e0a19bcbe

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crossover works
author Matt Johnston <matt@ucc.asn.au>
date Mon, 26 Oct 2020 23:06:41 +0800
parents 6dba84798cd5
children
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1471
6dba84798cd5 Update to libtomcrypt 1.18.1, merged with Dropbear changes
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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: $Format:%ai$ */