Mercurial > dropbear

annotate src/pk/asn1/der/integer/der_decode_integer.c @ 280:59400faa4b44 libtomcrypt-orig libtomcrypt-1.05

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Re-import libtomcrypt 1.05 for cleaner propagating. From crypt-1.05.tar.bz2, SHA1 of 88250202bb51570dc64f7e8f1c943cda9479258f
author Matt Johnston <matt@ucc.asn.au>
date Wed, 08 Mar 2006 12:58:00 +0000
parents
children d5faf4814ddb
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rev   line source
280
59400faa4b44 Re-import libtomcrypt 1.05 for cleaner propagating.
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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 $ */