Added intermediate casts to void* to prevent spurious warnings (with Clang and -Wcast...
[BearSSL] / src / symcipher / poly1305_ctmul.c
1 /*
2 * Copyright (c) 2016 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 * Perform the inner processing of blocks for Poly1305. The accumulator
29 * and the r key are provided as arrays of 26-bit words (these words
30 * are allowed to have an extra bit, i.e. use 27 bits).
31 *
32 * On output, all accumulator words fit on 26 bits, except acc[1], which
33 * may be slightly larger (but by a very small amount only).
34 */
35 static void
36 poly1305_inner(uint32_t *acc, const uint32_t *r, const void *data, size_t len)
37 {
38 /*
39 * Implementation notes: we split the 130-bit values into five
40 * 26-bit words. This gives us some space for carries.
41 *
42 * This code is inspired from the public-domain code available
43 * on:
44 * https://github.com/floodyberry/poly1305-donna
45 *
46 * Since we compute modulo 2^130-5, the "upper words" become
47 * low words with a factor of 5; that is, x*2^130 = x*5 mod p.
48 */
49 const unsigned char *buf;
50 uint32_t a0, a1, a2, a3, a4;
51 uint32_t r0, r1, r2, r3, r4;
52 uint32_t u1, u2, u3, u4;
53
54 r0 = r[0];
55 r1 = r[1];
56 r2 = r[2];
57 r3 = r[3];
58 r4 = r[4];
59
60 u1 = r1 * 5;
61 u2 = r2 * 5;
62 u3 = r3 * 5;
63 u4 = r4 * 5;
64
65 a0 = acc[0];
66 a1 = acc[1];
67 a2 = acc[2];
68 a3 = acc[3];
69 a4 = acc[4];
70
71 buf = data;
72 while (len > 0) {
73 uint64_t w0, w1, w2, w3, w4;
74 uint64_t c;
75 unsigned char tmp[16];
76
77 /*
78 * If there is a partial block, right-pad it with zeros.
79 */
80 if (len < 16) {
81 memset(tmp, 0, sizeof tmp);
82 memcpy(tmp, buf, len);
83 buf = tmp;
84 len = 16;
85 }
86
87 /*
88 * Decode next block and apply the "high bit"; that value
89 * is added to the accumulator.
90 */
91 a0 += br_dec32le(buf) & 0x03FFFFFF;
92 a1 += (br_dec32le(buf + 3) >> 2) & 0x03FFFFFF;
93 a2 += (br_dec32le(buf + 6) >> 4) & 0x03FFFFFF;
94 a3 += (br_dec32le(buf + 9) >> 6) & 0x03FFFFFF;
95 a4 += (br_dec32le(buf + 12) >> 8) | 0x01000000;
96
97 /*
98 * Compute multiplication.
99 */
100 #define M(x, y) ((uint64_t)(x) * (uint64_t)(y))
101
102 w0 = M(a0, r0) + M(a1, u4) + M(a2, u3) + M(a3, u2) + M(a4, u1);
103 w1 = M(a0, r1) + M(a1, r0) + M(a2, u4) + M(a3, u3) + M(a4, u2);
104 w2 = M(a0, r2) + M(a1, r1) + M(a2, r0) + M(a3, u4) + M(a4, u3);
105 w3 = M(a0, r3) + M(a1, r2) + M(a2, r1) + M(a3, r0) + M(a4, u4);
106 w4 = M(a0, r4) + M(a1, r3) + M(a2, r2) + M(a3, r1) + M(a4, r0);
107
108 #undef M
109 /*
110 * Perform some (partial) modular reduction. This step is
111 * enough to keep values in ranges such that there won't
112 * be carry overflows. Most of the reduction was done in
113 * the multiplication step (by using the 'u*' values, and
114 * using the fact that 2^130 = -5 mod p); here we perform
115 * some carry propagation.
116 */
117 c = w0 >> 26;
118 a0 = (uint32_t)w0 & 0x3FFFFFF;
119 w1 += c;
120 c = w1 >> 26;
121 a1 = (uint32_t)w1 & 0x3FFFFFF;
122 w2 += c;
123 c = w2 >> 26;
124 a2 = (uint32_t)w2 & 0x3FFFFFF;
125 w3 += c;
126 c = w3 >> 26;
127 a3 = (uint32_t)w3 & 0x3FFFFFF;
128 w4 += c;
129 c = w4 >> 26;
130 a4 = (uint32_t)w4 & 0x3FFFFFF;
131 a0 += (uint32_t)c * 5;
132 a1 += a0 >> 26;
133 a0 &= 0x3FFFFFF;
134
135 buf += 16;
136 len -= 16;
137 }
138
139 acc[0] = a0;
140 acc[1] = a1;
141 acc[2] = a2;
142 acc[3] = a3;
143 acc[4] = a4;
144 }
145
146 /* see bearssl_block.h */
147 void
148 br_poly1305_ctmul_run(const void *key, const void *iv,
149 void *data, size_t len, const void *aad, size_t aad_len,
150 void *tag, br_chacha20_run ichacha, int encrypt)
151 {
152 unsigned char pkey[32], foot[16];
153 uint32_t r[5], acc[5], cc, ctl, hi;
154 uint64_t w;
155 int i;
156
157 /*
158 * Compute the MAC key. The 'r' value is the first 16 bytes of
159 * pkey[].
160 */
161 memset(pkey, 0, sizeof pkey);
162 ichacha(key, iv, 0, pkey, sizeof pkey);
163
164 /*
165 * If encrypting, ChaCha20 must run first, followed by Poly1305.
166 * When decrypting, the operations are reversed.
167 */
168 if (encrypt) {
169 ichacha(key, iv, 1, data, len);
170 }
171
172 /*
173 * Run Poly1305. We must process the AAD, then ciphertext, then
174 * the footer (with the lengths). Note that the AAD and ciphertext
175 * are meant to be padded with zeros up to the next multiple of 16,
176 * and the length of the footer is 16 bytes as well.
177 */
178
179 /*
180 * Decode the 'r' value into 26-bit words, with the "clamping"
181 * operation applied.
182 */
183 r[0] = br_dec32le(pkey) & 0x03FFFFFF;
184 r[1] = (br_dec32le(pkey + 3) >> 2) & 0x03FFFF03;
185 r[2] = (br_dec32le(pkey + 6) >> 4) & 0x03FFC0FF;
186 r[3] = (br_dec32le(pkey + 9) >> 6) & 0x03F03FFF;
187 r[4] = (br_dec32le(pkey + 12) >> 8) & 0x000FFFFF;
188
189 /*
190 * Accumulator is 0.
191 */
192 memset(acc, 0, sizeof acc);
193
194 /*
195 * Process the additional authenticated data, ciphertext, and
196 * footer in due order.
197 */
198 br_enc64le(foot, (uint64_t)aad_len);
199 br_enc64le(foot + 8, (uint64_t)len);
200 poly1305_inner(acc, r, aad, aad_len);
201 poly1305_inner(acc, r, data, len);
202 poly1305_inner(acc, r, foot, sizeof foot);
203
204 /*
205 * Finalise modular reduction. This is done with carry propagation
206 * and applying the '2^130 = -5 mod p' rule. Note that the output
207 * of poly1035_inner() is already mostly reduced, since only
208 * acc[1] may be (very slightly) above 2^26. A single loop back
209 * to acc[1] will be enough to make the value fit in 130 bits.
210 */
211 cc = 0;
212 for (i = 1; i <= 6; i ++) {
213 int j;
214
215 j = (i >= 5) ? i - 5 : i;
216 acc[j] += cc;
217 cc = acc[j] >> 26;
218 acc[j] &= 0x03FFFFFF;
219 }
220
221 /*
222 * We may still have a value in the 2^130-5..2^130-1 range, in
223 * which case we must reduce it again. The code below selects,
224 * in constant-time, between 'acc' and 'acc-p',
225 */
226 ctl = GT(acc[0], 0x03FFFFFA);
227 for (i = 1; i < 5; i ++) {
228 ctl &= EQ(acc[i], 0x03FFFFFF);
229 }
230 cc = 5;
231 for (i = 0; i < 5; i ++) {
232 uint32_t t;
233
234 t = (acc[i] + cc);
235 cc = t >> 26;
236 t &= 0x03FFFFFF;
237 acc[i] = MUX(ctl, t, acc[i]);
238 }
239
240 /*
241 * Convert back the accumulator to 32-bit words, and add the
242 * 's' value (second half of pkey[]). That addition is done
243 * modulo 2^128.
244 */
245 w = (uint64_t)acc[0] + ((uint64_t)acc[1] << 26) + br_dec32le(pkey + 16);
246 br_enc32le((unsigned char *)tag, (uint32_t)w);
247 w = (w >> 32) + ((uint64_t)acc[2] << 20) + br_dec32le(pkey + 20);
248 br_enc32le((unsigned char *)tag + 4, (uint32_t)w);
249 w = (w >> 32) + ((uint64_t)acc[3] << 14) + br_dec32le(pkey + 24);
250 br_enc32le((unsigned char *)tag + 8, (uint32_t)w);
251 hi = (uint32_t)(w >> 32) + (acc[4] << 8) + br_dec32le(pkey + 28);
252 br_enc32le((unsigned char *)tag + 12, hi);
253
254 /*
255 * If decrypting, then ChaCha20 runs _after_ Poly1305.
256 */
257 if (!encrypt) {
258 ichacha(key, iv, 1, data, len);
259 }
260 }