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1 /* LibTomMath, multiple-precision integer library -- Tom St Denis |
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2 * |
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3 * LibTomMath is a library that provides multiple-precision |
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4 * integer arithmetic as well as number theoretic functionality. |
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5 * |
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6 * The library was designed directly after the MPI library by |
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7 * Michael Fromberger but has been written from scratch with |
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8 * additional optimizations in place. |
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9 * |
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10 * The library is free for all purposes without any express |
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11 * guarantee it works. |
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12 * |
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13 * Tom St Denis, [email protected], http://math.libtomcrypt.org |
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14 */ |
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15 #include <tommath.h> |
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16 |
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17 /* makes a truly random prime of a given size (bits), |
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18 * |
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19 * Flags are as follows: |
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20 * |
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21 * LTM_PRIME_BBS - make prime congruent to 3 mod 4 |
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22 * LTM_PRIME_SAFE - make sure (p-1)/2 is prime as well (implies LTM_PRIME_BBS) |
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23 * LTM_PRIME_2MSB_OFF - make the 2nd highest bit zero |
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24 * LTM_PRIME_2MSB_ON - make the 2nd highest bit one |
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25 * |
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26 * You have to supply a callback which fills in a buffer with random bytes. "dat" is a parameter you can |
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27 * have passed to the callback (e.g. a state or something). This function doesn't use "dat" itself |
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28 * so it can be NULL |
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29 * |
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30 */ |
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31 |
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32 /* This is possibly the mother of all prime generation functions, muahahahahaha! */ |
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33 int mp_prime_random_ex(mp_int *a, int t, int size, int flags, ltm_prime_callback cb, void *dat) |
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34 { |
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35 unsigned char *tmp, maskAND, maskOR_msb, maskOR_lsb; |
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36 int res, err, bsize, maskOR_msb_offset; |
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37 |
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38 /* sanity check the input */ |
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39 if (size <= 1 || t <= 0) { |
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40 return MP_VAL; |
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41 } |
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42 |
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43 /* LTM_PRIME_SAFE implies LTM_PRIME_BBS */ |
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44 if (flags & LTM_PRIME_SAFE) { |
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45 flags |= LTM_PRIME_BBS; |
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46 } |
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47 |
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48 /* calc the byte size */ |
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49 bsize = (size>>3)+(size&7?1:0); |
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50 |
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51 /* we need a buffer of bsize bytes */ |
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52 tmp = OPT_CAST(unsigned char) XMALLOC(bsize); |
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53 if (tmp == NULL) { |
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54 return MP_MEM; |
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55 } |
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56 |
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57 /* calc the maskAND value for the MSbyte*/ |
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58 maskAND = 0xFF >> (8 - (size & 7)); |
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59 |
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60 /* calc the maskOR_msb */ |
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61 maskOR_msb = 0; |
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62 maskOR_msb_offset = (size - 2) >> 3; |
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63 if (flags & LTM_PRIME_2MSB_ON) { |
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64 maskOR_msb |= 1 << ((size - 2) & 7); |
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65 } else if (flags & LTM_PRIME_2MSB_OFF) { |
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66 maskAND &= ~(1 << ((size - 2) & 7)); |
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67 } |
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68 |
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69 /* get the maskOR_lsb */ |
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70 maskOR_lsb = 0; |
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71 if (flags & LTM_PRIME_BBS) { |
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72 maskOR_lsb |= 3; |
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73 } |
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74 |
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75 do { |
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76 /* read the bytes */ |
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77 if (cb(tmp, bsize, dat) != bsize) { |
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78 err = MP_VAL; |
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79 goto error; |
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80 } |
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81 |
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82 /* work over the MSbyte */ |
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83 tmp[0] &= maskAND; |
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84 tmp[0] |= 1 << ((size - 1) & 7); |
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85 |
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86 /* mix in the maskORs */ |
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87 tmp[maskOR_msb_offset] |= maskOR_msb; |
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88 tmp[bsize-1] |= maskOR_lsb; |
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89 |
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90 /* read it in */ |
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91 if ((err = mp_read_unsigned_bin(a, tmp, bsize)) != MP_OKAY) { goto error; } |
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92 |
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93 /* is it prime? */ |
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94 if ((err = mp_prime_is_prime(a, t, &res)) != MP_OKAY) { goto error; } |
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95 |
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96 if (flags & LTM_PRIME_SAFE) { |
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97 /* see if (a-1)/2 is prime */ |
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98 if ((err = mp_sub_d(a, 1, a)) != MP_OKAY) { goto error; } |
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99 if ((err = mp_div_2(a, a)) != MP_OKAY) { goto error; } |
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100 |
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101 /* is it prime? */ |
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102 if ((err = mp_prime_is_prime(a, t, &res)) != MP_OKAY) { goto error; } |
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103 } |
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104 } while (res == MP_NO); |
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105 |
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106 if (flags & LTM_PRIME_SAFE) { |
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107 /* restore a to the original value */ |
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108 if ((err = mp_mul_2(a, a)) != MP_OKAY) { goto error; } |
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109 if ((err = mp_add_d(a, 1, a)) != MP_OKAY) { goto error; } |
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110 } |
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111 |
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112 err = MP_OKAY; |
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113 error: |
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114 XFREE(tmp); |
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115 return err; |
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116 } |
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117 |
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118 |
