1 | /* |
2 | * Copyright 1995-2017 The OpenSSL Project Authors. All Rights Reserved. |
3 | * |
4 | * Licensed under the Apache License 2.0 (the "License"). You may not use |
5 | * this file except in compliance with the License. You can obtain a copy |
6 | * in the file LICENSE in the source distribution or at |
7 | * https://www.openssl.org/source/license.html |
8 | */ |
9 | |
10 | #include <stdio.h> |
11 | #include "internal/cryptlib.h" |
12 | #include "bn_local.h" |
13 | |
14 | #define TABLE_SIZE 32 |
15 | |
16 | int BN_mod_exp2_mont(BIGNUM *rr, const BIGNUM *a1, const BIGNUM *p1, |
17 | const BIGNUM *a2, const BIGNUM *p2, const BIGNUM *m, |
18 | BN_CTX *ctx, BN_MONT_CTX *in_mont) |
19 | { |
20 | int i, j, bits, b, bits1, bits2, ret = |
21 | 0, wpos1, wpos2, window1, window2, wvalue1, wvalue2; |
22 | int r_is_one = 1; |
23 | BIGNUM *d, *r; |
24 | const BIGNUM *a_mod_m; |
25 | /* Tables of variables obtained from 'ctx' */ |
26 | BIGNUM *val1[TABLE_SIZE], *val2[TABLE_SIZE]; |
27 | BN_MONT_CTX *mont = NULL; |
28 | |
29 | bn_check_top(a1); |
30 | bn_check_top(p1); |
31 | bn_check_top(a2); |
32 | bn_check_top(p2); |
33 | bn_check_top(m); |
34 | |
35 | if (!(m->d[0] & 1)) { |
36 | BNerr(BN_F_BN_MOD_EXP2_MONT, BN_R_CALLED_WITH_EVEN_MODULUS); |
37 | return 0; |
38 | } |
39 | bits1 = BN_num_bits(p1); |
40 | bits2 = BN_num_bits(p2); |
41 | if ((bits1 == 0) && (bits2 == 0)) { |
42 | ret = BN_one(rr); |
43 | return ret; |
44 | } |
45 | |
46 | bits = (bits1 > bits2) ? bits1 : bits2; |
47 | |
48 | BN_CTX_start(ctx); |
49 | d = BN_CTX_get(ctx); |
50 | r = BN_CTX_get(ctx); |
51 | val1[0] = BN_CTX_get(ctx); |
52 | val2[0] = BN_CTX_get(ctx); |
53 | if (val2[0] == NULL) |
54 | goto err; |
55 | |
56 | if (in_mont != NULL) |
57 | mont = in_mont; |
58 | else { |
59 | if ((mont = BN_MONT_CTX_new()) == NULL) |
60 | goto err; |
61 | if (!BN_MONT_CTX_set(mont, m, ctx)) |
62 | goto err; |
63 | } |
64 | |
65 | window1 = BN_window_bits_for_exponent_size(bits1); |
66 | window2 = BN_window_bits_for_exponent_size(bits2); |
67 | |
68 | /* |
69 | * Build table for a1: val1[i] := a1^(2*i + 1) mod m for i = 0 .. 2^(window1-1) |
70 | */ |
71 | if (a1->neg || BN_ucmp(a1, m) >= 0) { |
72 | if (!BN_mod(val1[0], a1, m, ctx)) |
73 | goto err; |
74 | a_mod_m = val1[0]; |
75 | } else |
76 | a_mod_m = a1; |
77 | if (BN_is_zero(a_mod_m)) { |
78 | BN_zero(rr); |
79 | ret = 1; |
80 | goto err; |
81 | } |
82 | |
83 | if (!BN_to_montgomery(val1[0], a_mod_m, mont, ctx)) |
84 | goto err; |
85 | if (window1 > 1) { |
86 | if (!BN_mod_mul_montgomery(d, val1[0], val1[0], mont, ctx)) |
87 | goto err; |
88 | |
89 | j = 1 << (window1 - 1); |
90 | for (i = 1; i < j; i++) { |
91 | if (((val1[i] = BN_CTX_get(ctx)) == NULL) || |
92 | !BN_mod_mul_montgomery(val1[i], val1[i - 1], d, mont, ctx)) |
93 | goto err; |
94 | } |
95 | } |
96 | |
97 | /* |
98 | * Build table for a2: val2[i] := a2^(2*i + 1) mod m for i = 0 .. 2^(window2-1) |
99 | */ |
100 | if (a2->neg || BN_ucmp(a2, m) >= 0) { |
101 | if (!BN_mod(val2[0], a2, m, ctx)) |
102 | goto err; |
103 | a_mod_m = val2[0]; |
104 | } else |
105 | a_mod_m = a2; |
106 | if (BN_is_zero(a_mod_m)) { |
107 | BN_zero(rr); |
108 | ret = 1; |
109 | goto err; |
110 | } |
111 | if (!BN_to_montgomery(val2[0], a_mod_m, mont, ctx)) |
112 | goto err; |
113 | if (window2 > 1) { |
114 | if (!BN_mod_mul_montgomery(d, val2[0], val2[0], mont, ctx)) |
115 | goto err; |
116 | |
117 | j = 1 << (window2 - 1); |
118 | for (i = 1; i < j; i++) { |
119 | if (((val2[i] = BN_CTX_get(ctx)) == NULL) || |
120 | !BN_mod_mul_montgomery(val2[i], val2[i - 1], d, mont, ctx)) |
121 | goto err; |
122 | } |
123 | } |
124 | |
125 | /* Now compute the power product, using independent windows. */ |
126 | r_is_one = 1; |
127 | wvalue1 = 0; /* The 'value' of the first window */ |
128 | wvalue2 = 0; /* The 'value' of the second window */ |
129 | wpos1 = 0; /* If wvalue1 > 0, the bottom bit of the |
130 | * first window */ |
131 | wpos2 = 0; /* If wvalue2 > 0, the bottom bit of the |
132 | * second window */ |
133 | |
134 | if (!BN_to_montgomery(r, BN_value_one(), mont, ctx)) |
135 | goto err; |
136 | for (b = bits - 1; b >= 0; b--) { |
137 | if (!r_is_one) { |
138 | if (!BN_mod_mul_montgomery(r, r, r, mont, ctx)) |
139 | goto err; |
140 | } |
141 | |
142 | if (!wvalue1) |
143 | if (BN_is_bit_set(p1, b)) { |
144 | /* |
145 | * consider bits b-window1+1 .. b for this window |
146 | */ |
147 | i = b - window1 + 1; |
148 | while (!BN_is_bit_set(p1, i)) /* works for i<0 */ |
149 | i++; |
150 | wpos1 = i; |
151 | wvalue1 = 1; |
152 | for (i = b - 1; i >= wpos1; i--) { |
153 | wvalue1 <<= 1; |
154 | if (BN_is_bit_set(p1, i)) |
155 | wvalue1++; |
156 | } |
157 | } |
158 | |
159 | if (!wvalue2) |
160 | if (BN_is_bit_set(p2, b)) { |
161 | /* |
162 | * consider bits b-window2+1 .. b for this window |
163 | */ |
164 | i = b - window2 + 1; |
165 | while (!BN_is_bit_set(p2, i)) |
166 | i++; |
167 | wpos2 = i; |
168 | wvalue2 = 1; |
169 | for (i = b - 1; i >= wpos2; i--) { |
170 | wvalue2 <<= 1; |
171 | if (BN_is_bit_set(p2, i)) |
172 | wvalue2++; |
173 | } |
174 | } |
175 | |
176 | if (wvalue1 && b == wpos1) { |
177 | /* wvalue1 is odd and < 2^window1 */ |
178 | if (!BN_mod_mul_montgomery(r, r, val1[wvalue1 >> 1], mont, ctx)) |
179 | goto err; |
180 | wvalue1 = 0; |
181 | r_is_one = 0; |
182 | } |
183 | |
184 | if (wvalue2 && b == wpos2) { |
185 | /* wvalue2 is odd and < 2^window2 */ |
186 | if (!BN_mod_mul_montgomery(r, r, val2[wvalue2 >> 1], mont, ctx)) |
187 | goto err; |
188 | wvalue2 = 0; |
189 | r_is_one = 0; |
190 | } |
191 | } |
192 | if (!BN_from_montgomery(rr, r, mont, ctx)) |
193 | goto err; |
194 | ret = 1; |
195 | err: |
196 | if (in_mont == NULL) |
197 | BN_MONT_CTX_free(mont); |
198 | BN_CTX_end(ctx); |
199 | bn_check_top(rr); |
200 | return ret; |
201 | } |
202 | |