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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 "mycrypt.h" |
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12 |
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13 /* PKCS #1 v1.5 Signature Padding -- Tom St Denis */ |
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14 |
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15 #ifdef PKCS_1 |
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16 |
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17 int pkcs_1_v15_sa_decode(const unsigned char *msghash, unsigned long msghashlen, |
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18 const unsigned char *sig, unsigned long siglen, |
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19 int hash_idx, unsigned long modulus_bitlen, |
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20 int *res) |
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21 { |
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22 unsigned long x, y, modulus_bytelen, derlen; |
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23 int err; |
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24 |
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25 _ARGCHK(msghash != NULL); |
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26 _ARGCHK(sig != NULL); |
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27 _ARGCHK(res != NULL); |
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28 |
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29 /* default to invalid */ |
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30 *res = 0; |
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31 |
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32 /* valid hash ? */ |
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33 if ((err = hash_is_valid(hash_idx)) != CRYPT_OK) { |
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34 return err; |
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35 } |
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36 |
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37 /* get derlen */ |
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38 derlen = hash_descriptor[hash_idx].DERlen; |
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39 |
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40 /* get modulus len */ |
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41 modulus_bytelen = (modulus_bitlen>>3) + (modulus_bitlen & 7 ? 1 : 0); |
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42 |
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43 /* valid sizes? */ |
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44 if ((msghashlen + 3 + derlen > modulus_bytelen) || (siglen != modulus_bytelen)) { |
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45 return CRYPT_PK_INVALID_SIZE; |
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46 } |
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47 |
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48 /* packet is 0x00 0x01 PS 0x00 T, where PS == 0xFF repeated modulus_bytelen - 3 - derlen - msghashlen times, T == DER || hash */ |
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49 x = 0; |
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50 if (sig[x++] != 0x00 || sig[x++] != 0x01) { |
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51 return CRYPT_OK; |
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52 } |
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53 |
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54 /* now follows (modulus_bytelen - 3 - derlen - msghashlen) 0xFF bytes */ |
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55 for (y = 0; y < (modulus_bytelen - 3 - derlen - msghashlen); y++) { |
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56 if (sig[x++] != 0xFF) { |
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57 return CRYPT_OK; |
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58 } |
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59 } |
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60 |
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61 if (sig[x++] != 0x00) { |
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62 return CRYPT_OK; |
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63 } |
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64 |
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65 for (y = 0; y < derlen; y++) { |
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66 if (sig[x++] != hash_descriptor[hash_idx].DER[y]) { |
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67 return CRYPT_OK; |
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68 } |
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69 } |
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70 |
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71 if (memcmp(msghash, sig+x, msghashlen) == 0) { |
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72 *res = 1; |
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73 } |
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74 return CRYPT_OK; |
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75 } |
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76 |
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77 #endif |
