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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 der_decode_integer.c |
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15 ASN.1 DER, decode an integer, Tom St Denis |
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16 */ |
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17 |
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18 |
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19 #ifdef LTC_DER |
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20 |
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21 /** |
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22 Read a mp_int integer |
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23 @param in The DER encoded data |
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24 @param inlen Size of DER encoded data |
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25 @param num The first mp_int to decode |
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26 @return CRYPT_OK if successful |
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27 */ |
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28 int der_decode_integer(const unsigned char *in, unsigned long inlen, mp_int *num) |
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29 { |
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30 unsigned long x, y, z; |
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31 int err; |
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32 |
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33 LTC_ARGCHK(num != NULL); |
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34 LTC_ARGCHK(in != NULL); |
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35 |
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36 /* min DER INTEGER is 0x02 01 00 == 0 */ |
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37 if (inlen < (1 + 1 + 1)) { |
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38 return CRYPT_INVALID_PACKET; |
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39 } |
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40 |
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41 /* ok expect 0x02 when we AND with 0001 1111 [1F] */ |
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42 x = 0; |
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43 if ((in[x++] & 0x1F) != 0x02) { |
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44 return CRYPT_INVALID_PACKET; |
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45 } |
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46 |
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47 /* now decode the len stuff */ |
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48 z = in[x++]; |
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49 |
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50 if ((z & 0x80) == 0x00) { |
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51 /* short form */ |
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52 |
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53 /* will it overflow? */ |
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54 if (x + z > inlen) { |
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55 return CRYPT_INVALID_PACKET; |
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56 } |
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57 |
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58 /* no so read it */ |
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59 if ((err = mpi_to_ltc_error(mp_read_unsigned_bin(num, (unsigned char *)in + x, z))) != CRYPT_OK) { |
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60 return err; |
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61 } |
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62 } else { |
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63 /* long form */ |
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64 z &= 0x7F; |
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65 |
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66 /* will number of length bytes overflow? (or > 4) */ |
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67 if (((x + z) > inlen) || (z > 4) || (z == 0)) { |
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68 return CRYPT_INVALID_PACKET; |
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69 } |
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70 |
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71 /* now read it in */ |
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72 y = 0; |
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73 while (z--) { |
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74 y = ((unsigned long)(in[x++])) | (y << 8); |
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75 } |
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76 |
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77 /* now will reading y bytes overrun? */ |
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78 if ((x + y) > inlen) { |
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79 return CRYPT_INVALID_PACKET; |
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80 } |
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81 |
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82 /* no so read it */ |
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83 if ((err = mpi_to_ltc_error(mp_read_unsigned_bin(num, (unsigned char *)in + x, y))) != CRYPT_OK) { |
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84 return err; |
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85 } |
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86 } |
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87 |
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88 /* see if it's negative */ |
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89 if (in[x] & 0x80) { |
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90 mp_int tmp; |
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91 if (mp_init(&tmp) != MP_OKAY) { |
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92 return CRYPT_MEM; |
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93 } |
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94 |
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95 if (mp_2expt(&tmp, mp_count_bits(num)) != MP_OKAY || mp_sub(num, &tmp, num) != MP_OKAY) { |
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96 mp_clear(&tmp); |
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97 return CRYPT_MEM; |
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98 } |
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99 mp_clear(&tmp); |
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100 } |
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101 |
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102 return CRYPT_OK; |
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103 |
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104 } |
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105 |
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106 #endif |
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107 |
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108 /* $Source: /cvs/libtom/libtomcrypt/src/pk/asn1/der/integer/der_decode_integer.c,v $ */ |
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109 /* $Revision: 1.2 $ */ |
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110 /* $Date: 2005/06/01 00:06:05 $ */ |
