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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 /* performs a variable number of rounds of Miller-Rabin |
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18 * |
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19 * Probability of error after t rounds is no more than |
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20 * (1/4)^t when 1 <= t <= PRIME_SIZE |
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21 * |
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22 * Sets result to 1 if probably prime, 0 otherwise |
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23 */ |
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24 int mp_prime_is_prime (mp_int * a, int t, int *result) |
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25 { |
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26 mp_int b; |
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27 int ix, err, res; |
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28 |
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29 /* default to no */ |
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30 *result = MP_NO; |
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31 |
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32 /* valid value of t? */ |
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33 if (t <= 0 || t > PRIME_SIZE) { |
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34 return MP_VAL; |
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35 } |
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36 |
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37 /* is the input equal to one of the primes in the table? */ |
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38 for (ix = 0; ix < PRIME_SIZE; ix++) { |
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39 if (mp_cmp_d(a, __prime_tab[ix]) == MP_EQ) { |
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40 *result = 1; |
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41 return MP_OKAY; |
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42 } |
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43 } |
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44 |
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45 /* first perform trial division */ |
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46 if ((err = mp_prime_is_divisible (a, &res)) != MP_OKAY) { |
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47 return err; |
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48 } |
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49 |
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50 /* return if it was trivially divisible */ |
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51 if (res == MP_YES) { |
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52 return MP_OKAY; |
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53 } |
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54 |
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55 /* now perform the miller-rabin rounds */ |
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56 if ((err = mp_init (&b)) != MP_OKAY) { |
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57 return err; |
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58 } |
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59 |
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60 for (ix = 0; ix < t; ix++) { |
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61 /* set the prime */ |
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62 mp_set (&b, __prime_tab[ix]); |
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63 |
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64 if ((err = mp_prime_miller_rabin (a, &b, &res)) != MP_OKAY) { |
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65 goto __B; |
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66 } |
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67 |
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68 if (res == MP_NO) { |
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69 goto __B; |
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70 } |
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71 } |
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72 |
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73 /* passed the test */ |
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74 *result = MP_YES; |
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75 __B:mp_clear (&b); |
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76 return err; |
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77 } |
