Mercurial > dropbear

annotate src/pk/asn1/der/der_decode_integer.c @ 191:1c15b283127b libtomcrypt-orig

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Import of libtomcrypt 1.02 with manual path rename rearrangement etc
author Matt Johnston <matt@ucc.asn.au>
date Fri, 06 May 2005 13:23:02 +0000
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1c15b283127b Import of libtomcrypt 1.02 with manual path rename rearrangement etc
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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 /* decodes a DER INTEGER in [in]. You have to tell this function
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22 * how many bytes are available [inlen]. It will then attempt to
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23 * read the INTEGER. If all goes well it stores the number of bytes
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24 * read in [inlen] and the number in [num].
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25 */
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26 /**
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27 Read a mp_int integer
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28 @param in The DER encoded data
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29 @param inlen [in] Size of the in data, [out] number of bytes read
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30 @param num The first mp_int to decode
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31 @return CRYPT_OK if successful
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32 */
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33 int der_decode_integer(const unsigned char *in, unsigned long *inlen, mp_int *num)
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34 {
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35 unsigned long tmplen, y, z;
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36
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37 LTC_ARGCHK(num != NULL);
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38 LTC_ARGCHK(in != NULL);
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39 LTC_ARGCHK(inlen != NULL);
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40
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41 /* save copy of max output size */
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42 tmplen = *inlen;
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43 *inlen = 0;
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44
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45 /* min DER INTEGER is 0x02 01 00 == 0 */
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46 if (tmplen < (1 + 1 + 1)) {
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47 return CRYPT_INVALID_PACKET;
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48 }
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49
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50 /* ok expect 0x02 when we AND with 0011 1111 [3F] */
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51 if ((*in++ & 0x3F) != 0x02) {
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52 return CRYPT_INVALID_PACKET;
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53 }
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54 ++(*inlen);
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55
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56 /* now decode the len stuff */
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57 z = *in++;
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58 ++(*inlen);
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59
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60 if ((z & 0x80) == 0x00) {
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61 /* short form */
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62
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63 /* will it overflow? */
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64 if (*inlen + z > tmplen) {
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65 return CRYPT_INVALID_PACKET;
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66 }
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67
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68 /* no so read it */
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69 (*inlen) += z;
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70 return mpi_to_ltc_error(mp_read_unsigned_bin(num, (unsigned char *)in, z));
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71 } else {
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72 /* long form */
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73 z &= 0x7F;
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74
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75 /* will number of length bytes overflow? (or > 4) */
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76 if (((*inlen + z) > tmplen) || (z > 4)) {
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77 return CRYPT_INVALID_PACKET;
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78 }
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79
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80 /* now read it in */
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81 y = 0;
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82 while (z--) {
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83 y = ((unsigned long)(*in++)) | (y << 8);
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84 ++(*inlen);
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85 }
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86
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87 /* now will reading y bytes overrun? */
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88 if ((*inlen + y) > tmplen) {
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89 return CRYPT_INVALID_PACKET;
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90 }
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91
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92 /* no so read it */
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93 (*inlen) += y;
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94 return mpi_to_ltc_error(mp_read_unsigned_bin(num, (unsigned char *)in, y));
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95 }
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96 }
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97
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98 #endif