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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 /* determines if a number is a valid DR modulus */ |
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18 int mp_dr_is_modulus(mp_int *a) |
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19 { |
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20 int ix; |
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21 |
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22 /* must be at least two digits */ |
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23 if (a->used < 2) { |
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24 return 0; |
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25 } |
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26 |
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27 /* must be of the form b**k - a [a <= b] so all |
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28 * but the first digit must be equal to -1 (mod b). |
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29 */ |
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30 for (ix = 1; ix < a->used; ix++) { |
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31 if (a->dp[ix] != MP_MASK) { |
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32 return 0; |
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33 } |
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34 } |
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35 return 1; |
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36 } |
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37 |
