_ Git - BearSSL/blob - src/int/i15_ext1.c

   1 /*
   2  * Copyright (c) 2017 Thomas Pornin <pornin@bolet.org>
   3  *
   4  * Permission is hereby granted, free of charge, to any person obtaining
   5  * a copy of this software and associated documentation files (the
   6  * "Software"), to deal in the Software without restriction, including
   7  * without limitation the rights to use, copy, modify, merge, publish,
   8  * distribute, sublicense, and/or sell copies of the Software, and to
   9  * permit persons to whom the Software is furnished to do so, subject to
  10  * the following conditions:
  11  *
  12  * The above copyright notice and this permission notice shall be
  13  * included in all copies or substantial portions of the Software.
  14  *
  15  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  16  * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  17  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  18  * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
  19  * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
  20  * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
  21  * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  22  * SOFTWARE.
  23  */
  24
  25 #include "inner.h"
  26
  27 /*
  28  * This file contains some additional functions for "i15" big integers.
  29  * These functions are needed to support ECDSA.
  30  */
  31
  32 /* see inner.h */
  33 void
  34 br_i15_rshift(uint16_t *x, int count)
  35 {
  36         size_t u, len;
  37         unsigned r;
  38
  39         len = (x[0] + 15) >> 4;
  40         if (len == 0) {
  41                 return;
  42         }
  43         r = x[1] >> count;
  44         for (u = 2; u <= len; u ++) {
  45                 unsigned w;
  46
  47                 w = x[u];
  48                 x[u - 1] = ((w << (15 - count)) | r) & 0x7FFF;
  49                 r = w >> count;
  50         }
  51         x[len] = r;
  52 }
  53
  54 /* see inner.h */
  55 uint32_t
  56 br_i15_bit_length(uint16_t *x, size_t xlen)
  57 {
  58         uint32_t tw, twk;
  59
  60         tw = 0;
  61         twk = 0;
  62         while (xlen -- > 0) {
  63                 uint32_t w, c;
  64
  65                 c = EQ(tw, 0);
  66                 w = x[xlen];
  67                 tw = MUX(c, w, tw);
  68                 twk = MUX(c, (uint32_t)xlen, twk);
  69         }
  70         return (twk << 4) + BIT_LENGTH(tw);
  71 }
  72
  73 /* see inner.h */
  74 void
  75 br_i15_decode(uint16_t *x, const void *src, size_t len)
  76 {
  77         const unsigned char *buf;
  78         size_t v;
  79         uint32_t acc;
  80         int acc_len;
  81
  82         buf = src;
  83         v = 1;
  84         acc = 0;
  85         acc_len = 0;
  86         while (len -- > 0) {
  87                 uint32_t b;
  88
  89                 b = buf[len];
  90                 acc |= (b << acc_len);
  91                 acc_len += 8;
  92                 if (acc_len >= 15) {
  93                         x[v ++] = acc & 0x7FFF;
  94                         acc_len -= 15;
  95                         acc >>= 15;
  96                 }
  97         }
  98         if (acc_len != 0) {
  99                 x[v ++] = acc;
 100         }
 101         x[0] = br_i15_bit_length(x + 1, v - 1);
 102 }
 103
 104 /* see inner.h */
 105 void
 106 br_i15_from_monty(uint16_t *x, const uint16_t *m, uint16_t m0i)
 107 {
 108         size_t len, u, v;
 109
 110         len = (m[0] + 15) >> 4;
 111         for (u = 0; u < len; u ++) {
 112                 uint32_t f, cc;
 113
 114                 f = MUL15(x[1], m0i) & 0x7FFF;
 115                 cc = 0;
 116                 for (v = 0; v < len; v ++) {
 117                         uint32_t z;
 118
 119                         z = (uint32_t)x[v + 1] + MUL15(f, m[v + 1]) + cc;
 120                         cc = z >> 15;
 121                         if (v != 0) {
 122                                 x[v] = z & 0x7FFF;
 123                         }
 124                 }
 125                 x[len] = cc;
 126         }
 127
 128         /*
 129          * We may have to do an extra subtraction, but only if the
 130          * value in x[] is indeed greater than or equal to that of m[],
 131          * which is why we must do two calls (first call computes the
 132          * carry, second call performs the subtraction only if the carry
 133          * is 0).
 134          */
 135         br_i15_sub(x, m, NOT(br_i15_sub(x, m, 0)));
 136 }