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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_encode_short_integer.c |
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15 ASN.1 DER, encode 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 /* Exports a positive integer as DER format (upto 32-bits in size) */ |
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22 /** |
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23 Store a mp_int integer |
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24 @param num The integer to encode |
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25 @param out [out] The destination for the DER encoded integers |
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26 @param outlen [in/out] The max size and resulting size of the DER encoded integers |
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27 @return CRYPT_OK if successful |
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28 */ |
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29 int der_encode_short_integer(unsigned long num, unsigned char *out, unsigned long *outlen) |
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30 { |
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31 unsigned long len, x, y, z; |
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32 int err; |
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33 |
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34 LTC_ARGCHK(out != NULL); |
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35 LTC_ARGCHK(outlen != NULL); |
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36 |
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37 /* force to 32 bits */ |
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38 num &= 0xFFFFFFFFUL; |
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39 |
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40 /* find out how big this will be */ |
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41 if ((err = der_length_short_integer(num, &len)) != CRYPT_OK) { |
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42 return err; |
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43 } |
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44 |
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45 if (*outlen < len) { |
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46 return CRYPT_BUFFER_OVERFLOW; |
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47 } |
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48 |
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49 /* get len of output */ |
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50 z = 0; |
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51 y = num; |
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52 while (y) { |
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53 ++z; |
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54 y >>= 8; |
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55 } |
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56 |
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57 /* handle zero */ |
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58 if (z == 0) { |
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59 z = 1; |
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60 } |
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61 |
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62 /* see if msb is set */ |
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63 z += (num&(1UL<<((z<<3) - 1))) ? 1 : 0; |
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64 |
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65 /* adjust the number so the msB is non-zero */ |
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66 for (x = 0; (z <= 4) && (x < (4 - z)); x++) { |
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67 num <<= 8; |
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68 } |
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69 |
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70 /* store header */ |
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71 x = 0; |
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72 out[x++] = 0x02; |
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73 out[x++] = z; |
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74 |
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75 /* if 31st bit is set output a leading zero and decrement count */ |
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76 if (z == 5) { |
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77 out[x++] = 0; |
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78 --z; |
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79 } |
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80 |
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81 /* store values */ |
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82 for (y = 0; y < z; y++) { |
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83 out[x++] = (num >> 24) & 0xFF; |
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84 num <<= 8; |
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85 } |
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86 |
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87 /* we good */ |
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88 *outlen = x; |
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89 |
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90 return CRYPT_OK; |
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91 } |
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92 |
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93 #endif |
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94 |
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95 /* $Source: /cvs/libtom/libtomcrypt/src/pk/asn1/der/short_integer/der_encode_short_integer.c,v $ */ |
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96 /* $Revision: 1.3 $ */ |
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97 /* $Date: 2005/05/23 01:27:03 $ */ |
