Mercurial > dropbear

annotate src/pk/pkcs1/pkcs_1_v15_es_decode.c @ 199:8be64e2c86f4 libtomcrypt

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* SMALL_CODE is now LTC_SMALL_CODE
author Matt Johnston <matt@ucc.asn.au>
date Tue, 10 May 2005 17:02:59 +0000
parents 1c15b283127b
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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9 * Tom St Denis, [email protected], http://libtomcrypt.org
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10 */
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11 #include "tomcrypt.h"
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12
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13 /**
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14 @file pkcs_1_v15_es_decode.c
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15 PKCS #1 v1.5 Encryption Padding, Tom St Denis
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16 */
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17
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18 #ifdef PKCS_1
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19
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20 /**
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21 PKCS #1 v1.5 Encryption Decoding
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22 @param msg The padded data
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23 @param msglen The length of the padded data (octets)
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24 @param modulus_bitlen The bit length of the RSA modulus
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25 @param out [out] Where to store the decoded data
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26 @param outlen The length of the decoded data
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27 @param res [out] Result of the decoding, 1==valid, 0==invalid
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28 @return CRYPT_OK if successful
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29 */
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30 int pkcs_1_v15_es_decode(const unsigned char *msg, unsigned long msglen,
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31 unsigned long modulus_bitlen,
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32 unsigned char *out, unsigned long outlen,
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33 int *res)
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34 {
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35 unsigned long x, modulus_bytelen;
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36
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37 LTC_ARGCHK(msg != NULL);
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38 LTC_ARGCHK(out != NULL);
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39 LTC_ARGCHK(res != NULL);
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40
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41 /* default to failed */
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42 *res = 0;
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43
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44 modulus_bytelen = (modulus_bitlen>>3) + (modulus_bitlen & 7 ? 1 : 0);
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45
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46 /* must be at least modulus_bytelen bytes long */
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47 if (msglen != modulus_bytelen) {
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48 return CRYPT_INVALID_ARG;
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49 }
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50
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51 /* should start with 0x00 0x02 */
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52 if (msg[0] != 0x00 || msg[1] != 0x02) {
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53 return CRYPT_OK;
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54 }
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55
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56 /* skip over PS */
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57 x = 2 + (modulus_bytelen - outlen - 3);
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58
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59 /* should be 0x00 */
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60 if (msg[x++] != 0x00) {
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61 return CRYPT_OK;
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62 }
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63
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64 /* the message is left */
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65 if (x + outlen > modulus_bytelen) {
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66 return CRYPT_PK_INVALID_SIZE;
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67 }
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68 XMEMCPY(out, msg + x, outlen);
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69 *res = 1;
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70 return CRYPT_OK;
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71 }
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72
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73 #endif
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74