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1/* $OpenBSD: ge25519.c,v 1.3 2013/12/09 11:03:45 markus Exp $ */
2
3/*
4 * Public Domain, Authors: Daniel J. Bernstein, Niels Duif, Tanja Lange,
5 * Peter Schwabe, Bo-Yin Yang.
6 * Copied from supercop-20130419/crypto_sign/ed25519/ref/ge25519.c
7 */
8
9#include "includes.h"
10
11#include "fe25519.h"
12#include "sc25519.h"
13#include "ge25519.h"
14
15/*
16 * Arithmetic on the twisted Edwards curve -x^2 + y^2 = 1 + dx^2y^2
17 * with d = -(121665/121666) = 37095705934669439343138083508754565189542113879843219016388785533085940283555
18 * Base point: (15112221349535400772501151409588531511454012693041857206046113283949847762202,46316835694926478169428394003475163141307993866256225615783033603165251855960);
19 */
20
21/* d */
22static const fe25519 ge25519_ecd = {{0xA3, 0x78, 0x59, 0x13, 0xCA, 0x4D, 0xEB, 0x75, 0xAB, 0xD8, 0x41, 0x41, 0x4D, 0x0A, 0x70, 0x00,
23 0x98, 0xE8, 0x79, 0x77, 0x79, 0x40, 0xC7, 0x8C, 0x73, 0xFE, 0x6F, 0x2B, 0xEE, 0x6C, 0x03, 0x52}};
24/* 2*d */
25static const fe25519 ge25519_ec2d = {{0x59, 0xF1, 0xB2, 0x26, 0x94, 0x9B, 0xD6, 0xEB, 0x56, 0xB1, 0x83, 0x82, 0x9A, 0x14, 0xE0, 0x00,
26 0x30, 0xD1, 0xF3, 0xEE, 0xF2, 0x80, 0x8E, 0x19, 0xE7, 0xFC, 0xDF, 0x56, 0xDC, 0xD9, 0x06, 0x24}};
27/* sqrt(-1) */
28static const fe25519 ge25519_sqrtm1 = {{0xB0, 0xA0, 0x0E, 0x4A, 0x27, 0x1B, 0xEE, 0xC4, 0x78, 0xE4, 0x2F, 0xAD, 0x06, 0x18, 0x43, 0x2F,
29 0xA7, 0xD7, 0xFB, 0x3D, 0x99, 0x00, 0x4D, 0x2B, 0x0B, 0xDF, 0xC1, 0x4F, 0x80, 0x24, 0x83, 0x2B}};
30
31#define ge25519_p3 ge25519
32
33typedef struct
34{
35 fe25519 x;
36 fe25519 z;
37 fe25519 y;
38 fe25519 t;
39} ge25519_p1p1;
40
41typedef struct
42{
43 fe25519 x;
44 fe25519 y;
45 fe25519 z;
46} ge25519_p2;
47
48typedef struct
49{
50 fe25519 x;
51 fe25519 y;
52} ge25519_aff;
53
54
55/* Packed coordinates of the base point */
56const ge25519 ge25519_base = {{{0x1A, 0xD5, 0x25, 0x8F, 0x60, 0x2D, 0x56, 0xC9, 0xB2, 0xA7, 0x25, 0x95, 0x60, 0xC7, 0x2C, 0x69,
57 0x5C, 0xDC, 0xD6, 0xFD, 0x31, 0xE2, 0xA4, 0xC0, 0xFE, 0x53, 0x6E, 0xCD, 0xD3, 0x36, 0x69, 0x21}},
58 {{0x58, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66,
59 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66}},
60 {{0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
61 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00}},
62 {{0xA3, 0xDD, 0xB7, 0xA5, 0xB3, 0x8A, 0xDE, 0x6D, 0xF5, 0x52, 0x51, 0x77, 0x80, 0x9F, 0xF0, 0x20,
63 0x7D, 0xE3, 0xAB, 0x64, 0x8E, 0x4E, 0xEA, 0x66, 0x65, 0x76, 0x8B, 0xD7, 0x0F, 0x5F, 0x87, 0x67}}};
64
65/* Multiples of the base point in affine representation */
66static const ge25519_aff ge25519_base_multiples_affine[425] = {
67#include "ge25519_base.data"
68};
69
70static void p1p1_to_p2(ge25519_p2 *r, const ge25519_p1p1 *p)
71{
72 fe25519_mul(&r->x, &p->x, &p->t);
73 fe25519_mul(&r->y, &p->y, &p->z);
74 fe25519_mul(&r->z, &p->z, &p->t);
75}
76
77static void p1p1_to_p3(ge25519_p3 *r, const ge25519_p1p1 *p)
78{
79 p1p1_to_p2((ge25519_p2 *)r, p);
80 fe25519_mul(&r->t, &p->x, &p->y);
81}
82
83static void ge25519_mixadd2(ge25519_p3 *r, const ge25519_aff *q)
84{
85 fe25519 a,b,t1,t2,c,d,e,f,g,h,qt;
86 fe25519_mul(&qt, &q->x, &q->y);
87 fe25519_sub(&a, &r->y, &r->x); /* A = (Y1-X1)*(Y2-X2) */
88 fe25519_add(&b, &r->y, &r->x); /* B = (Y1+X1)*(Y2+X2) */
89 fe25519_sub(&t1, &q->y, &q->x);
90 fe25519_add(&t2, &q->y, &q->x);
91 fe25519_mul(&a, &a, &t1);
92 fe25519_mul(&b, &b, &t2);
93 fe25519_sub(&e, &b, &a); /* E = B-A */
94 fe25519_add(&h, &b, &a); /* H = B+A */
95 fe25519_mul(&c, &r->t, &qt); /* C = T1*k*T2 */
96 fe25519_mul(&c, &c, &ge25519_ec2d);
97 fe25519_add(&d, &r->z, &r->z); /* D = Z1*2 */
98 fe25519_sub(&f, &d, &c); /* F = D-C */
99 fe25519_add(&g, &d, &c); /* G = D+C */
100 fe25519_mul(&r->x, &e, &f);
101 fe25519_mul(&r->y, &h, &g);
102 fe25519_mul(&r->z, &g, &f);
103 fe25519_mul(&r->t, &e, &h);
104}
105
106static void add_p1p1(ge25519_p1p1 *r, const ge25519_p3 *p, const ge25519_p3 *q)
107{
108 fe25519 a, b, c, d, t;
109
110 fe25519_sub(&a, &p->y, &p->x); /* A = (Y1-X1)*(Y2-X2) */
111 fe25519_sub(&t, &q->y, &q->x);
112 fe25519_mul(&a, &a, &t);
113 fe25519_add(&b, &p->x, &p->y); /* B = (Y1+X1)*(Y2+X2) */
114 fe25519_add(&t, &q->x, &q->y);
115 fe25519_mul(&b, &b, &t);
116 fe25519_mul(&c, &p->t, &q->t); /* C = T1*k*T2 */
117 fe25519_mul(&c, &c, &ge25519_ec2d);
118 fe25519_mul(&d, &p->z, &q->z); /* D = Z1*2*Z2 */
119 fe25519_add(&d, &d, &d);
120 fe25519_sub(&r->x, &b, &a); /* E = B-A */
121 fe25519_sub(&r->t, &d, &c); /* F = D-C */
122 fe25519_add(&r->z, &d, &c); /* G = D+C */
123 fe25519_add(&r->y, &b, &a); /* H = B+A */
124}
125
126/* See http://www.hyperelliptic.org/EFD/g1p/auto-twisted-extended-1.html#doubling-dbl-2008-hwcd */
127static void dbl_p1p1(ge25519_p1p1 *r, const ge25519_p2 *p)
128{
129 fe25519 a,b,c,d;
130 fe25519_square(&a, &p->x);
131 fe25519_square(&b, &p->y);
132 fe25519_square(&c, &p->z);
133 fe25519_add(&c, &c, &c);
134 fe25519_neg(&d, &a);
135
136 fe25519_add(&r->x, &p->x, &p->y);
137 fe25519_square(&r->x, &r->x);
138 fe25519_sub(&r->x, &r->x, &a);
139 fe25519_sub(&r->x, &r->x, &b);
140 fe25519_add(&r->z, &d, &b);
141 fe25519_sub(&r->t, &r->z, &c);
142 fe25519_sub(&r->y, &d, &b);
143}
144
145/* Constant-time version of: if(b) r = p */
146static void cmov_aff(ge25519_aff *r, const ge25519_aff *p, unsigned char b)
147{
148 fe25519_cmov(&r->x, &p->x, b);
149 fe25519_cmov(&r->y, &p->y, b);
150}
151
152static unsigned char equal(signed char b,signed char c)
153{
154 unsigned char ub = b;
155 unsigned char uc = c;
156 unsigned char x = ub ^ uc; /* 0: yes; 1..255: no */
157 crypto_uint32 y = x; /* 0: yes; 1..255: no */
158 y -= 1; /* 4294967295: yes; 0..254: no */
159 y >>= 31; /* 1: yes; 0: no */
160 return y;
161}
162
163static unsigned char negative(signed char b)
164{
165 unsigned long long x = b; /* 18446744073709551361..18446744073709551615: yes; 0..255: no */
166 x >>= 63; /* 1: yes; 0: no */
167 return x;
168}
169
170static void choose_t(ge25519_aff *t, unsigned long long pos, signed char b)
171{
172 /* constant time */
173 fe25519 v;
174 *t = ge25519_base_multiples_affine[5*pos+0];
175 cmov_aff(t, &ge25519_base_multiples_affine[5*pos+1],equal(b,1) | equal(b,-1));
176 cmov_aff(t, &ge25519_base_multiples_affine[5*pos+2],equal(b,2) | equal(b,-2));
177 cmov_aff(t, &ge25519_base_multiples_affine[5*pos+3],equal(b,3) | equal(b,-3));
178 cmov_aff(t, &ge25519_base_multiples_affine[5*pos+4],equal(b,-4));
179 fe25519_neg(&v, &t->x);
180 fe25519_cmov(&t->x, &v, negative(b));
181}
182
183static void setneutral(ge25519 *r)
184{
185 fe25519_setzero(&r->x);
186 fe25519_setone(&r->y);
187 fe25519_setone(&r->z);
188 fe25519_setzero(&r->t);
189}
190
191/* ********************************************************************
192 * EXPORTED FUNCTIONS
193 ******************************************************************** */
194
195/* return 0 on success, -1 otherwise */
196int ge25519_unpackneg_vartime(ge25519_p3 *r, const unsigned char p[32])
197{
198 unsigned char par;
199 fe25519 t, chk, num, den, den2, den4, den6;
200 fe25519_setone(&r->z);
201 par = p[31] >> 7;
202 fe25519_unpack(&r->y, p);
203 fe25519_square(&num, &r->y); /* x = y^2 */
204 fe25519_mul(&den, &num, &ge25519_ecd); /* den = dy^2 */
205 fe25519_sub(&num, &num, &r->z); /* x = y^2-1 */
206 fe25519_add(&den, &r->z, &den); /* den = dy^2+1 */
207
208 /* Computation of sqrt(num/den) */
209 /* 1.: computation of num^((p-5)/8)*den^((7p-35)/8) = (num*den^7)^((p-5)/8) */
210 fe25519_square(&den2, &den);
211 fe25519_square(&den4, &den2);
212 fe25519_mul(&den6, &den4, &den2);
213 fe25519_mul(&t, &den6, &num);
214 fe25519_mul(&t, &t, &den);
215
216 fe25519_pow2523(&t, &t);
217 /* 2. computation of r->x = t * num * den^3 */
218 fe25519_mul(&t, &t, &num);
219 fe25519_mul(&t, &t, &den);
220 fe25519_mul(&t, &t, &den);
221 fe25519_mul(&r->x, &t, &den);
222
223 /* 3. Check whether sqrt computation gave correct result, multiply by sqrt(-1) if not: */
224 fe25519_square(&chk, &r->x);
225 fe25519_mul(&chk, &chk, &den);
226 if (!fe25519_iseq_vartime(&chk, &num))
227 fe25519_mul(&r->x, &r->x, &ge25519_sqrtm1);
228
229 /* 4. Now we have one of the two square roots, except if input was not a square */
230 fe25519_square(&chk, &r->x);
231 fe25519_mul(&chk, &chk, &den);
232 if (!fe25519_iseq_vartime(&chk, &num))
233 return -1;
234
235 /* 5. Choose the desired square root according to parity: */
236 if(fe25519_getparity(&r->x) != (1-par))
237 fe25519_neg(&r->x, &r->x);
238
239 fe25519_mul(&r->t, &r->x, &r->y);
240 return 0;
241}
242
243void ge25519_pack(unsigned char r[32], const ge25519_p3 *p)
244{
245 fe25519 tx, ty, zi;
246 fe25519_invert(&zi, &p->z);
247 fe25519_mul(&tx, &p->x, &zi);
248 fe25519_mul(&ty, &p->y, &zi);
249 fe25519_pack(r, &ty);
250 r[31] ^= fe25519_getparity(&tx) << 7;
251}
252
253int ge25519_isneutral_vartime(const ge25519_p3 *p)
254{
255 int ret = 1;
256 if(!fe25519_iszero(&p->x)) ret = 0;
257 if(!fe25519_iseq_vartime(&p->y, &p->z)) ret = 0;
258 return ret;
259}
260
261/* computes [s1]p1 + [s2]p2 */
262void ge25519_double_scalarmult_vartime(ge25519_p3 *r, const ge25519_p3 *p1, const sc25519 *s1, const ge25519_p3 *p2, const sc25519 *s2)
263{
264 ge25519_p1p1 tp1p1;
265 ge25519_p3 pre[16];
266 unsigned char b[127];
267 int i;
268
269 /* precomputation s2 s1 */
270 setneutral(pre); /* 00 00 */
271 pre[1] = *p1; /* 00 01 */
272 dbl_p1p1(&tp1p1,(ge25519_p2 *)p1); p1p1_to_p3( &pre[2], &tp1p1); /* 00 10 */
273 add_p1p1(&tp1p1,&pre[1], &pre[2]); p1p1_to_p3( &pre[3], &tp1p1); /* 00 11 */
274 pre[4] = *p2; /* 01 00 */
275 add_p1p1(&tp1p1,&pre[1], &pre[4]); p1p1_to_p3( &pre[5], &tp1p1); /* 01 01 */
276 add_p1p1(&tp1p1,&pre[2], &pre[4]); p1p1_to_p3( &pre[6], &tp1p1); /* 01 10 */
277 add_p1p1(&tp1p1,&pre[3], &pre[4]); p1p1_to_p3( &pre[7], &tp1p1); /* 01 11 */
278 dbl_p1p1(&tp1p1,(ge25519_p2 *)p2); p1p1_to_p3( &pre[8], &tp1p1); /* 10 00 */
279 add_p1p1(&tp1p1,&pre[1], &pre[8]); p1p1_to_p3( &pre[9], &tp1p1); /* 10 01 */
280 dbl_p1p1(&tp1p1,(ge25519_p2 *)&pre[5]); p1p1_to_p3(&pre[10], &tp1p1); /* 10 10 */
281 add_p1p1(&tp1p1,&pre[3], &pre[8]); p1p1_to_p3(&pre[11], &tp1p1); /* 10 11 */
282 add_p1p1(&tp1p1,&pre[4], &pre[8]); p1p1_to_p3(&pre[12], &tp1p1); /* 11 00 */
283 add_p1p1(&tp1p1,&pre[1],&pre[12]); p1p1_to_p3(&pre[13], &tp1p1); /* 11 01 */
284 add_p1p1(&tp1p1,&pre[2],&pre[12]); p1p1_to_p3(&pre[14], &tp1p1); /* 11 10 */
285 add_p1p1(&tp1p1,&pre[3],&pre[12]); p1p1_to_p3(&pre[15], &tp1p1); /* 11 11 */
286
287 sc25519_2interleave2(b,s1,s2);
288
289 /* scalar multiplication */
290 *r = pre[b[126]];
291 for(i=125;i>=0;i--)
292 {
293 dbl_p1p1(&tp1p1, (ge25519_p2 *)r);
294 p1p1_to_p2((ge25519_p2 *) r, &tp1p1);
295 dbl_p1p1(&tp1p1, (ge25519_p2 *)r);
296 if(b[i]!=0)
297 {
298 p1p1_to_p3(r, &tp1p1);
299 add_p1p1(&tp1p1, r, &pre[b[i]]);
300 }
301 if(i != 0) p1p1_to_p2((ge25519_p2 *)r, &tp1p1);
302 else p1p1_to_p3(r, &tp1p1);
303 }
304}
305
306void ge25519_scalarmult_base(ge25519_p3 *r, const sc25519 *s)
307{
308 signed char b[85];
309 int i;
310 ge25519_aff t;
311 sc25519_window3(b,s);
312
313 choose_t((ge25519_aff *)r, 0, b[0]);
314 fe25519_setone(&r->z);
315 fe25519_mul(&r->t, &r->x, &r->y);
316 for(i=1;i<85;i++)
317 {
318 choose_t(&t, (unsigned long long) i, b[i]);
319 ge25519_mixadd2(r, &t);
320 }
321}
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