1 /* $OpenBSD: poly1305.c,v 1.2 2020/07/22 13:54:30 tobhe Exp $ */
2 /*
3 * Public Domain poly1305 from Andrew Moon
4 * Based on poly1305-donna.c, poly1305-donna-32.h and poly1305-donna.h from:
5 * https://github.com/floodyberry/poly1305-donna
6 */
7
8 #include <sys/types.h>
9 #include <sys/systm.h>
10
11 #include "poly1305.h"
12
13 /*
14 * poly1305 implementation using 32 bit * 32 bit = 64 bit multiplication
15 * and 64 bit addition.
16 */
17
18 /* interpret four 8 bit unsigned integers as a 32 bit unsigned integer in little endian */
19 static unsigned long
U8TO32(const unsigned char * p)20 U8TO32(const unsigned char *p)
21 {
22 return (((unsigned long)(p[0] & 0xff)) |
23 ((unsigned long)(p[1] & 0xff) << 8) |
24 ((unsigned long)(p[2] & 0xff) << 16) |
25 ((unsigned long)(p[3] & 0xff) << 24));
26 }
27
28 /* store a 32 bit unsigned integer as four 8 bit unsigned integers in little endian */
29 static void
U32TO8(unsigned char * p,unsigned long v)30 U32TO8(unsigned char *p, unsigned long v)
31 {
32 p[0] = (v) & 0xff;
33 p[1] = (v >> 8) & 0xff;
34 p[2] = (v >> 16) & 0xff;
35 p[3] = (v >> 24) & 0xff;
36 }
37
38 void
poly1305_init(poly1305_state * st,const unsigned char key[32])39 poly1305_init(poly1305_state *st, const unsigned char key[32])
40 {
41 /* r &= 0xffffffc0ffffffc0ffffffc0fffffff */
42 st->r[0] = (U8TO32(&key[0])) & 0x3ffffff;
43 st->r[1] = (U8TO32(&key[3]) >> 2) & 0x3ffff03;
44 st->r[2] = (U8TO32(&key[6]) >> 4) & 0x3ffc0ff;
45 st->r[3] = (U8TO32(&key[9]) >> 6) & 0x3f03fff;
46 st->r[4] = (U8TO32(&key[12]) >> 8) & 0x00fffff;
47
48 /* h = 0 */
49 st->h[0] = 0;
50 st->h[1] = 0;
51 st->h[2] = 0;
52 st->h[3] = 0;
53 st->h[4] = 0;
54
55 /* save pad for later */
56 st->pad[0] = U8TO32(&key[16]);
57 st->pad[1] = U8TO32(&key[20]);
58 st->pad[2] = U8TO32(&key[24]);
59 st->pad[3] = U8TO32(&key[28]);
60
61 st->leftover = 0;
62 st->final = 0;
63 }
64
65 static void
poly1305_blocks(poly1305_state * st,const unsigned char * m,size_t bytes)66 poly1305_blocks(poly1305_state *st, const unsigned char *m, size_t bytes)
67 {
68 const unsigned long hibit = (st->final) ? 0 : (1 << 24); /* 1 << 128 */
69 unsigned long r0, r1, r2, r3, r4;
70 unsigned long s1, s2, s3, s4;
71 unsigned long h0, h1, h2, h3, h4;
72 unsigned long long d0, d1, d2, d3, d4;
73 unsigned long c;
74
75 r0 = st->r[0];
76 r1 = st->r[1];
77 r2 = st->r[2];
78 r3 = st->r[3];
79 r4 = st->r[4];
80
81 s1 = r1 * 5;
82 s2 = r2 * 5;
83 s3 = r3 * 5;
84 s4 = r4 * 5;
85
86 h0 = st->h[0];
87 h1 = st->h[1];
88 h2 = st->h[2];
89 h3 = st->h[3];
90 h4 = st->h[4];
91
92 while (bytes >= poly1305_block_size) {
93 /* h += m[i] */
94 h0 += (U8TO32(m + 0)) & 0x3ffffff;
95 h1 += (U8TO32(m + 3) >> 2) & 0x3ffffff;
96 h2 += (U8TO32(m + 6) >> 4) & 0x3ffffff;
97 h3 += (U8TO32(m + 9) >> 6) & 0x3ffffff;
98 h4 += (U8TO32(m + 12) >> 8) | hibit;
99
100 /* h *= r */
101 d0 = ((unsigned long long)h0 * r0) +
102 ((unsigned long long)h1 * s4) +
103 ((unsigned long long)h2 * s3) +
104 ((unsigned long long)h3 * s2) +
105 ((unsigned long long)h4 * s1);
106 d1 = ((unsigned long long)h0 * r1) +
107 ((unsigned long long)h1 * r0) +
108 ((unsigned long long)h2 * s4) +
109 ((unsigned long long)h3 * s3) +
110 ((unsigned long long)h4 * s2);
111 d2 = ((unsigned long long)h0 * r2) +
112 ((unsigned long long)h1 * r1) +
113 ((unsigned long long)h2 * r0) +
114 ((unsigned long long)h3 * s4) +
115 ((unsigned long long)h4 * s3);
116 d3 = ((unsigned long long)h0 * r3) +
117 ((unsigned long long)h1 * r2) +
118 ((unsigned long long)h2 * r1) +
119 ((unsigned long long)h3 * r0) +
120 ((unsigned long long)h4 * s4);
121 d4 = ((unsigned long long)h0 * r4) +
122 ((unsigned long long)h1 * r3) +
123 ((unsigned long long)h2 * r2) +
124 ((unsigned long long)h3 * r1) +
125 ((unsigned long long)h4 * r0);
126
127 /* (partial) h %= p */
128 c = (unsigned long)(d0 >> 26);
129 h0 = (unsigned long)d0 & 0x3ffffff;
130 d1 += c;
131 c = (unsigned long)(d1 >> 26);
132 h1 = (unsigned long)d1 & 0x3ffffff;
133 d2 += c;
134 c = (unsigned long)(d2 >> 26);
135 h2 = (unsigned long)d2 & 0x3ffffff;
136 d3 += c;
137 c = (unsigned long)(d3 >> 26);
138 h3 = (unsigned long)d3 & 0x3ffffff;
139 d4 += c;
140 c = (unsigned long)(d4 >> 26);
141 h4 = (unsigned long)d4 & 0x3ffffff;
142 h0 += c * 5;
143 c = (h0 >> 26);
144 h0 = h0 & 0x3ffffff;
145 h1 += c;
146
147 m += poly1305_block_size;
148 bytes -= poly1305_block_size;
149 }
150
151 st->h[0] = h0;
152 st->h[1] = h1;
153 st->h[2] = h2;
154 st->h[3] = h3;
155 st->h[4] = h4;
156 }
157
158 void
poly1305_update(poly1305_state * st,const unsigned char * m,size_t bytes)159 poly1305_update(poly1305_state *st, const unsigned char *m, size_t bytes)
160 {
161 size_t i;
162
163 /* handle leftover */
164 if (st->leftover) {
165 size_t want = (poly1305_block_size - st->leftover);
166 if (want > bytes)
167 want = bytes;
168 for (i = 0; i < want; i++)
169 st->buffer[st->leftover + i] = m[i];
170 bytes -= want;
171 m += want;
172 st->leftover += want;
173 if (st->leftover < poly1305_block_size)
174 return;
175 poly1305_blocks(st, st->buffer, poly1305_block_size);
176 st->leftover = 0;
177 }
178
179 /* process full blocks */
180 if (bytes >= poly1305_block_size) {
181 size_t want = (bytes & ~(poly1305_block_size - 1));
182 poly1305_blocks(st, m, want);
183 m += want;
184 bytes -= want;
185 }
186
187 /* store leftover */
188 if (bytes) {
189 for (i = 0; i < bytes; i++)
190 st->buffer[st->leftover + i] = m[i];
191 st->leftover += bytes;
192 }
193 }
194
195 void
poly1305_finish(poly1305_state * st,unsigned char mac[16])196 poly1305_finish(poly1305_state *st, unsigned char mac[16])
197 {
198 unsigned long h0, h1, h2, h3, h4, c;
199 unsigned long g0, g1, g2, g3, g4;
200 unsigned long long f;
201 unsigned long mask;
202
203 /* process the remaining block */
204 if (st->leftover) {
205 size_t i = st->leftover;
206 st->buffer[i++] = 1;
207 for (; i < poly1305_block_size; i++)
208 st->buffer[i] = 0;
209 st->final = 1;
210 poly1305_blocks(st, st->buffer, poly1305_block_size);
211 }
212
213 /* fully carry h */
214 h0 = st->h[0];
215 h1 = st->h[1];
216 h2 = st->h[2];
217 h3 = st->h[3];
218 h4 = st->h[4];
219
220 c = h1 >> 26;
221 h1 = h1 & 0x3ffffff;
222 h2 += c;
223 c = h2 >> 26;
224 h2 = h2 & 0x3ffffff;
225 h3 += c;
226 c = h3 >> 26;
227 h3 = h3 & 0x3ffffff;
228 h4 += c;
229 c = h4 >> 26;
230 h4 = h4 & 0x3ffffff;
231 h0 += c * 5;
232 c = h0 >> 26;
233 h0 = h0 & 0x3ffffff;
234 h1 += c;
235
236 /* compute h + -p */
237 g0 = h0 + 5;
238 c = g0 >> 26;
239 g0 &= 0x3ffffff;
240 g1 = h1 + c;
241 c = g1 >> 26;
242 g1 &= 0x3ffffff;
243 g2 = h2 + c;
244 c = g2 >> 26;
245 g2 &= 0x3ffffff;
246 g3 = h3 + c;
247 c = g3 >> 26;
248 g3 &= 0x3ffffff;
249 g4 = h4 + c - (1 << 26);
250
251 /* select h if h < p, or h + -p if h >= p */
252 mask = (g4 >> ((sizeof(unsigned long) * 8) - 1)) - 1;
253 g0 &= mask;
254 g1 &= mask;
255 g2 &= mask;
256 g3 &= mask;
257 g4 &= mask;
258 mask = ~mask;
259 h0 = (h0 & mask) | g0;
260 h1 = (h1 & mask) | g1;
261 h2 = (h2 & mask) | g2;
262 h3 = (h3 & mask) | g3;
263 h4 = (h4 & mask) | g4;
264
265 /* h = h % (2^128) */
266 h0 = ((h0) | (h1 << 26)) & 0xffffffff;
267 h1 = ((h1 >> 6) | (h2 << 20)) & 0xffffffff;
268 h2 = ((h2 >> 12) | (h3 << 14)) & 0xffffffff;
269 h3 = ((h3 >> 18) | (h4 << 8)) & 0xffffffff;
270
271 /* mac = (h + pad) % (2^128) */
272 f = (unsigned long long)h0 + st->pad[0];
273 h0 = (unsigned long)f;
274 f = (unsigned long long)h1 + st->pad[1] + (f >> 32);
275 h1 = (unsigned long)f;
276 f = (unsigned long long)h2 + st->pad[2] + (f >> 32);
277 h2 = (unsigned long)f;
278 f = (unsigned long long)h3 + st->pad[3] + (f >> 32);
279 h3 = (unsigned long)f;
280
281 U32TO8(mac + 0, h0);
282 U32TO8(mac + 4, h1);
283 U32TO8(mac + 8, h2);
284 U32TO8(mac + 12, h3);
285
286 /* zero out the state */
287 st->h[0] = 0;
288 st->h[1] = 0;
289 st->h[2] = 0;
290 st->h[3] = 0;
291 st->h[4] = 0;
292 st->r[0] = 0;
293 st->r[1] = 0;
294 st->r[2] = 0;
295 st->r[3] = 0;
296 st->r[4] = 0;
297 st->pad[0] = 0;
298 st->pad[1] = 0;
299 st->pad[2] = 0;
300 st->pad[3] = 0;
301 }
302