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annotate libtomcrypt/src/encauth/ocb3/ocb3_decrypt_last.c @ 1471:6dba84798cd5

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Update to libtomcrypt 1.18.1, merged with Dropbear changes
author Matt Johnston <matt@ucc.asn.au>
date Fri, 09 Feb 2018 21:44:05 +0800
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1471
6dba84798cd5 Update to libtomcrypt 1.18.1, merged with Dropbear changes
Matt Johnston <matt@ucc.asn.au>
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1 /* LibTomCrypt, modular cryptographic library -- Tom St Denis
6dba84798cd5 Update to libtomcrypt 1.18.1, merged with Dropbear changes
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2 *
6dba84798cd5 Update to libtomcrypt 1.18.1, merged with Dropbear changes
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3 * LibTomCrypt is a library that provides various cryptographic
6dba84798cd5 Update to libtomcrypt 1.18.1, merged with Dropbear changes
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4 * algorithms in a highly modular and flexible manner.
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5 *
6dba84798cd5 Update to libtomcrypt 1.18.1, merged with Dropbear changes
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6 * The library is free for all purposes without any express
6dba84798cd5 Update to libtomcrypt 1.18.1, merged with Dropbear changes
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7 * guarantee it works.
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8 */
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9
6dba84798cd5 Update to libtomcrypt 1.18.1, merged with Dropbear changes
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10 /**
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11 @file ocb3_decrypt_last.c
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12 OCB implementation, internal helper, by Karel Miko
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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 Finish an OCB (decryption) stream
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20 @param ocb The OCB state
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21 @param ct The remaining ciphertext
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22 @param ctlen The length of the ciphertext (octets)
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23 @param pt [out] The output buffer
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24 @return CRYPT_OK if successful
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25 */
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26 int ocb3_decrypt_last(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 iOffset_star[MAXBLOCKSIZE];
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29 unsigned char iPad[MAXBLOCKSIZE];
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30 int err, x, full_blocks, full_blocks_len, last_block_len;
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31
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32 LTC_ARGCHK(ocb != NULL);
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33 if (ct == NULL) LTC_ARGCHK(ctlen == 0);
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34 if (ctlen != 0) {
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35 LTC_ARGCHK(ct != NULL);
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36 LTC_ARGCHK(pt != NULL);
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37 }
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38
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39 if ((err = cipher_is_valid(ocb->cipher)) != CRYPT_OK) {
6dba84798cd5 Update to libtomcrypt 1.18.1, merged with Dropbear changes
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40 goto LBL_ERR;
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41 }
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42
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43 full_blocks = ctlen/ocb->block_len;
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44 full_blocks_len = full_blocks * ocb->block_len;
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45 last_block_len = ctlen - full_blocks_len;
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46
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47 /* process full blocks first */
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48 if (full_blocks>0) {
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49 if ((err = ocb3_decrypt(ocb, ct, full_blocks_len, pt)) != CRYPT_OK) {
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50 goto LBL_ERR;
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51 }
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52 }
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53
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54 if (last_block_len>0) {
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55 /* Offset_* = Offset_m xor L_* */
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56 ocb3_int_xor_blocks(iOffset_star, ocb->Offset_current, ocb->L_star, ocb->block_len);
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57
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58 /* Pad = ENCIPHER(K, Offset_*) */
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59 if ((err = cipher_descriptor[ocb->cipher].ecb_encrypt(iOffset_star, iPad, &ocb->key)) != CRYPT_OK) {
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60 goto LBL_ERR;
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61 }
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62
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63 /* P_* = C_* xor Pad[1..bitlen(C_*)] */
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64 ocb3_int_xor_blocks(pt+full_blocks_len, (unsigned char *)ct+full_blocks_len, iPad, last_block_len);
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65
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66 /* Checksum_* = Checksum_m xor (P_* || 1 || zeros(127-bitlen(P_*))) */
6dba84798cd5 Update to libtomcrypt 1.18.1, merged with Dropbear changes
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67 ocb3_int_xor_blocks(ocb->checksum, ocb->checksum, pt+full_blocks_len, last_block_len);
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68 for(x=last_block_len; x<ocb->block_len; x++) {
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69 if (x == last_block_len)
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70 ocb->checksum[x] ^= 0x80;
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71 else
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72 ocb->checksum[x] ^= 0x00;
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73 }
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74
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75 /* Tag = ENCIPHER(K, Checksum_* xor Offset_* xor L_$) xor HASH(K,A) */
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76 /* at this point we calculate only: Tag_part = ENCIPHER(K, Checksum_* xor Offset_* xor L_$) */
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77 for(x=0; x<ocb->block_len; x++) {
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78 ocb->tag_part[x] = (ocb->checksum[x] ^ iOffset_star[x]) ^ ocb->L_dollar[x];
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79 }
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80 if ((err = cipher_descriptor[ocb->cipher].ecb_encrypt(ocb->tag_part, ocb->tag_part, &ocb->key)) != CRYPT_OK) {
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81 goto LBL_ERR;
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82 }
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83 }
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84 else {
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85 /* Tag = ENCIPHER(K, Checksum_m xor Offset_m xor L_$) xor HASH(K,A) */
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86 /* at this point we calculate only: Tag_part = ENCIPHER(K, Checksum_m xor Offset_m xor L_$) */
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87 for(x=0; x<ocb->block_len; x++) {
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88 ocb->tag_part[x] = (ocb->checksum[x] ^ ocb->Offset_current[x]) ^ ocb->L_dollar[x];
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89 }
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90 if ((err = cipher_descriptor[ocb->cipher].ecb_encrypt(ocb->tag_part, ocb->tag_part, &ocb->key)) != CRYPT_OK) {
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91 goto LBL_ERR;
6dba84798cd5 Update to libtomcrypt 1.18.1, merged with Dropbear changes
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92 }
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93 }
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94
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95 err = CRYPT_OK;
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96
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97 LBL_ERR:
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98 #ifdef LTC_CLEAN_STACK
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99 zeromem(iOffset_star, MAXBLOCKSIZE);
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100 zeromem(iPad, MAXBLOCKSIZE);
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101 #endif
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102
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103 return err;
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104 }
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105
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106 #endif
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107
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108 /* ref: $Format:%D$ */
6dba84798cd5 Update to libtomcrypt 1.18.1, merged with Dropbear changes
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109 /* git commit: $Format:%H$ */
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110 /* commit time: $Format:%ai$ */