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annotate src/encauth/gcm/gcm_done.c @ 191:1c15b283127b libtomcrypt-orig

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Import of libtomcrypt 1.02 with manual path rename rearrangement etc
author Matt Johnston <matt@ucc.asn.au>
date Fri, 06 May 2005 13:23:02 +0000
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children 39d5d58461d6
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191
1c15b283127b Import of libtomcrypt 1.02 with manual path rename rearrangement etc
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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.org
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10 */
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11
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12 /**
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13 @file gcm_done.c
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14 GCM implementation, Terminate the stream, 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 GCM_MODE
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19
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20 /**
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21 Terminate a GCM stream
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22 @param gcm The GCM state
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23 @param tag [out] The destination for the MAC tag
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24 @param taglen [in/out] The length of the MAC tag
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25 @return CRYPT_OK on success
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26 */
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27 int gcm_done(gcm_state *gcm,
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28 unsigned char *tag, unsigned long *taglen)
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29 {
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30 unsigned long x;
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31 int err;
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32
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33 LTC_ARGCHK(gcm != NULL);
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34 LTC_ARGCHK(tag != NULL);
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35 LTC_ARGCHK(taglen != NULL);
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36
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37 if (gcm->buflen > 16 || gcm->buflen < 0) {
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38 return CRYPT_INVALID_ARG;
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39 }
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40
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41 if ((err = cipher_is_valid(gcm->cipher)) != CRYPT_OK) {
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42 return err;
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43 }
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44
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45
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46 if (gcm->mode != GCM_MODE_TEXT) {
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47 return CRYPT_INVALID_ARG;
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48 }
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49
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50 /* handle remaining ciphertext */
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51 if (gcm->buflen) {
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52 gcm->pttotlen += gcm->buflen * CONST64(8);
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53 gcm_mult_h(gcm, gcm->X);
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54 }
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55
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56 /* length */
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57 STORE64H(gcm->totlen, gcm->buf);
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58 STORE64H(gcm->pttotlen, gcm->buf+8);
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59 for (x = 0; x < 16; x++) {
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60 gcm->X[x] ^= gcm->buf[x];
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61 }
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62 gcm_mult_h(gcm, gcm->X);
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63
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64 /* encrypt original counter */
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65 cipher_descriptor[gcm->cipher].ecb_encrypt(gcm->Y_0, gcm->buf, &gcm->K);
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66 for (x = 0; x < 16 && x < *taglen; x++) {
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67 tag[x] = gcm->buf[x] ^ gcm->X[x];
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68 }
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69 *taglen = x;
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70
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71 cipher_descriptor[gcm->cipher].done(&gcm->K);
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72
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73 return CRYPT_OK;
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74 }
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75
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76 #endif
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77