Mercurial > dropbear

annotate libtomcrypt/src/encauth/ocb/ocb_decrypt.c @ 1555:2f0c3f3361d3

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Added tag DROPBEAR_2018.76 for changeset 1c66ca4f3791
author Matt Johnston <matt@ucc.asn.au>
date Tue, 27 Feb 2018 22:48:42 +0800
parents 6dba84798cd5
children
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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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10 /**
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11 @file ocb_decrypt.c
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6dba84798cd5 Update to libtomcrypt 1.18.1, merged with Dropbear changes
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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_OCB_MODE
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18 /**
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19 Decrypt a block with OCB.
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20 @param ocb The OCB state
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21 @param ct The ciphertext (length of the block size of the block cipher)
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22 @param pt [out] The plaintext (length of ct)
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23 @return CRYPT_OK if successful
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24 */
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25 int ocb_decrypt(ocb_state *ocb, const unsigned char *ct, unsigned char *pt)
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26 {
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27 unsigned char Z[MAXBLOCKSIZE], tmp[MAXBLOCKSIZE];
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28 int err, x;
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29
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30 LTC_ARGCHK(ocb != NULL);
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31 LTC_ARGCHK(pt != NULL);
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32 LTC_ARGCHK(ct != NULL);
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34 /* check if valid cipher */
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35 if ((err = cipher_is_valid(ocb->cipher)) != CRYPT_OK) {
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36 return err;
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37 }
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38 LTC_ARGCHK(cipher_descriptor[ocb->cipher].ecb_decrypt != NULL);
1471
6dba84798cd5 Update to libtomcrypt 1.18.1, merged with Dropbear changes
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39
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40 /* check length */
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41 if (ocb->block_len != cipher_descriptor[ocb->cipher].block_length) {
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42 return CRYPT_INVALID_ARG;
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43 }
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45 /* Get Z[i] value */
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46 ocb_shift_xor(ocb, Z);
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47
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48 /* xor ct in, encrypt, xor Z out */
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49 for (x = 0; x < ocb->block_len; x++) {
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50 tmp[x] = ct[x] ^ Z[x];
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51 }
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52 if ((err = cipher_descriptor[ocb->cipher].ecb_decrypt(tmp, pt, &ocb->key)) != CRYPT_OK) {
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53 return err;
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54 }
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55 for (x = 0; x < ocb->block_len; x++) {
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56 pt[x] ^= Z[x];
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57 }
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58
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59 /* compute checksum */
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60 for (x = 0; x < ocb->block_len; x++) {
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61 ocb->checksum[x] ^= pt[x];
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62 }
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65 #ifdef LTC_CLEAN_STACK
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66 zeromem(Z, sizeof(Z));
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67 zeromem(tmp, sizeof(tmp));
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68 #endif
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69 return CRYPT_OK;
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70 }
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72 #endif
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74
1471
6dba84798cd5 Update to libtomcrypt 1.18.1, merged with Dropbear changes
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75 /* ref: $Format:%D$ */
6dba84798cd5 Update to libtomcrypt 1.18.1, merged with Dropbear changes
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76 /* git commit: $Format:%H$ */
6dba84798cd5 Update to libtomcrypt 1.18.1, merged with Dropbear changes
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77 /* commit time: $Format:%ai$ */