66 lines
2.1 KiB
C
66 lines
2.1 KiB
C
/*
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* Copyright (c) 2016 Thomas Pornin <pornin@bolet.org>
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*
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* Permission is hereby granted, free of charge, to any person obtaining
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* a copy of this software and associated documentation files (the
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* "Software"), to deal in the Software without restriction, including
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* without limitation the rights to use, copy, modify, merge, publish,
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* distribute, sublicense, and/or sell copies of the Software, and to
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* permit persons to whom the Software is furnished to do so, subject to
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* the following conditions:
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*
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* The above copyright notice and this permission notice shall be
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* included in all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
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* BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
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* ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
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* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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* SOFTWARE.
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*/
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#include "inner.h"
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/* see inner.h */
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void
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br_i32_modpow(uint32_t *x,
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const unsigned char *e, size_t elen,
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const uint32_t *m, uint32_t m0i, uint32_t *t1, uint32_t *t2)
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{
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size_t mlen;
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uint32_t k;
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/*
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* 'mlen' is the length of m[] expressed in bytes (including
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* the "bit length" first field).
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*/
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mlen = ((m[0] + 63) >> 5) * sizeof m[0];
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/*
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* Throughout the algorithm:
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* -- t1[] is in Montgomery representation; it contains x, x^2,
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* x^4, x^8...
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* -- The result is accumulated, in normal representation, in
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* the x[] array.
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* -- t2[] is used as destination buffer for each multiplication.
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*
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* Note that there is no need to call br_i32_from_monty().
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*/
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memcpy(t1, x, mlen);
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br_i32_to_monty(t1, m);
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br_i32_zero(x, m[0]);
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x[1] = 1;
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for (k = 0; k < ((uint32_t)elen << 3); k ++) {
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uint32_t ctl;
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ctl = (e[elen - 1 - (k >> 3)] >> (k & 7)) & 1;
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br_i32_montymul(t2, x, t1, m, m0i);
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CCOPY(ctl, x, t2, mlen);
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br_i32_montymul(t2, t1, t1, m, m0i);
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memcpy(t1, t2, mlen);
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}
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}
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