Mercurial > dropbear

annotate src/pk/pkcs1/pkcs_1_v15_sa_decode.c @ 192:9cc34777b479 libtomcrypt

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propagate from branch 'au.asn.ucc.matt.ltc-orig' (head 9ba8f01f44320e9cb9f19881105ae84f84a43ea9) to branch 'au.asn.ucc.matt.dropbear.ltc' (head dbf51c569bc34956ad948e4cc87a0eeb2170b768)
author Matt Johnston <matt@ucc.asn.au>
date Sun, 08 May 2005 06:36:47 +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_sa_decode.c
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15 PKCS #1 v1.5 Signature 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 Perform PKCS #1 v1.5 Signature Decoding
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22 @param msghash The hash that was signed
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23 @param msghashlen The length of the hash
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24 @param sig The signature [padded data]
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25 @param siglen The length of the signature
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26 @param hash_idx The index of the hash used
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27 @param modulus_bitlen The bit length of the RSA modulus
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28 @param res [out] Result of comparison, 1==valid, 0==invalid
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29 @return CRYPT_OK if successful
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30 */
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31 int pkcs_1_v15_sa_decode(const unsigned char *msghash, unsigned long msghashlen,
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32 const unsigned char *sig, unsigned long siglen,
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33 int hash_idx, unsigned long modulus_bitlen,
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34 int *res)
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35 {
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36 unsigned long x, y, modulus_bytelen, derlen;
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37 int err;
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38
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39 LTC_ARGCHK(msghash != NULL);
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40 LTC_ARGCHK(sig != NULL);
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41 LTC_ARGCHK(res != NULL);
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42
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43 /* default to invalid */
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44 *res = 0;
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45
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46 /* valid hash ? */
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47 if ((err = hash_is_valid(hash_idx)) != CRYPT_OK) {
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48 return err;
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49 }
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50
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51 /* get derlen */
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52 derlen = hash_descriptor[hash_idx].DERlen;
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53
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54 /* get modulus len */
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55 modulus_bytelen = (modulus_bitlen>>3) + (modulus_bitlen & 7 ? 1 : 0);
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56
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57 /* valid sizes? */
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58 if ((msghashlen + 3 + derlen > modulus_bytelen) || (siglen != modulus_bytelen)) {
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59 return CRYPT_PK_INVALID_SIZE;
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60 }
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61
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62 /* packet is 0x00 0x01 PS 0x00 T, where PS == 0xFF repeated modulus_bytelen - 3 - derlen - msghashlen times, T == DER || hash */
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63 x = 0;
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64 if (sig[x++] != 0x00 || sig[x++] != 0x01) {
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65 return CRYPT_OK;
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66 }
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67
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68 /* now follows (modulus_bytelen - 3 - derlen - msghashlen) 0xFF bytes */
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69 for (y = 0; y < (modulus_bytelen - 3 - derlen - msghashlen); y++) {
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70 if (sig[x++] != 0xFF) {
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71 return CRYPT_OK;
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72 }
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73 }
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74
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75 if (sig[x++] != 0x00) {
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76 return CRYPT_OK;
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77 }
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78
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79 for (y = 0; y < derlen; y++) {
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80 if (sig[x++] != hash_descriptor[hash_idx].DER[y]) {
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81 return CRYPT_OK;
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82 }
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83 }
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84
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85 if (memcmp(msghash, sig+x, msghashlen) == 0) {
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86 *res = 1;
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87 }
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88 return CRYPT_OK;
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89 }
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90
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91 #endif