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365 lines
10 KiB
365 lines
10 KiB
/*
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conversions
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*/
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DONNA_INLINE static void
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ge25519_p1p1_to_partial(ge25519 *r, const ge25519_p1p1 *p) {
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curve25519_mul(r->x, p->x, p->t);
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curve25519_mul(r->y, p->y, p->z);
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curve25519_mul(r->z, p->z, p->t);
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}
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DONNA_INLINE static void
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ge25519_p1p1_to_full(ge25519 *r, const ge25519_p1p1 *p) {
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curve25519_mul(r->x, p->x, p->t);
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curve25519_mul(r->y, p->y, p->z);
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curve25519_mul(r->z, p->z, p->t);
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curve25519_mul(r->t, p->x, p->y);
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}
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static void
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ge25519_full_to_pniels(ge25519_pniels *p, const ge25519 *r) {
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curve25519_sub(p->ysubx, r->y, r->x);
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curve25519_add(p->xaddy, r->y, r->x);
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curve25519_copy(p->z, r->z);
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curve25519_mul(p->t2d, r->t, ge25519_ec2d);
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}
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/*
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adding & doubling
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*/
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static void
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ge25519_add_p1p1(ge25519_p1p1 *r, const ge25519 *p, const ge25519 *q) {
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bignum25519 a,b,c,d,t,u;
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curve25519_sub(a, p->y, p->x);
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curve25519_add(b, p->y, p->x);
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curve25519_sub(t, q->y, q->x);
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curve25519_add(u, q->y, q->x);
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curve25519_mul(a, a, t);
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curve25519_mul(b, b, u);
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curve25519_mul(c, p->t, q->t);
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curve25519_mul(c, c, ge25519_ec2d);
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curve25519_mul(d, p->z, q->z);
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curve25519_add(d, d, d);
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curve25519_sub(r->x, b, a);
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curve25519_add(r->y, b, a);
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curve25519_add_after_basic(r->z, d, c);
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curve25519_sub_after_basic(r->t, d, c);
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}
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static void
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ge25519_double_p1p1(ge25519_p1p1 *r, const ge25519 *p) {
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bignum25519 a,b,c;
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curve25519_square(a, p->x);
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curve25519_square(b, p->y);
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curve25519_square(c, p->z);
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curve25519_add_reduce(c, c, c);
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curve25519_add(r->x, p->x, p->y);
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curve25519_square(r->x, r->x);
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curve25519_add(r->y, b, a);
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curve25519_sub(r->z, b, a);
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curve25519_sub_after_basic(r->x, r->x, r->y);
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curve25519_sub_after_basic(r->t, c, r->z);
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}
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static void
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ge25519_nielsadd2_p1p1(ge25519_p1p1 *r, const ge25519 *p, const ge25519_niels *q, unsigned char signbit) {
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const bignum25519 *qb = (const bignum25519 *)q;
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bignum25519 *rb = (bignum25519 *)r;
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bignum25519 a,b,c;
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curve25519_sub(a, p->y, p->x);
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curve25519_add(b, p->y, p->x);
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curve25519_mul(a, a, qb[signbit]); /* x for +, y for - */
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curve25519_mul(r->x, b, qb[signbit^1]); /* y for +, x for - */
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curve25519_add(r->y, r->x, a);
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curve25519_sub(r->x, r->x, a);
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curve25519_mul(c, p->t, q->t2d);
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curve25519_add_reduce(r->t, p->z, p->z);
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curve25519_copy(r->z, r->t);
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curve25519_add(rb[2+signbit], rb[2+signbit], c); /* z for +, t for - */
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curve25519_sub(rb[2+(signbit^1)], rb[2+(signbit^1)], c); /* t for +, z for - */
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}
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static void
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ge25519_pnielsadd_p1p1(ge25519_p1p1 *r, const ge25519 *p, const ge25519_pniels *q, unsigned char signbit) {
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const bignum25519 *qb = (const bignum25519 *)q;
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bignum25519 *rb = (bignum25519 *)r;
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bignum25519 a,b,c;
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curve25519_sub(a, p->y, p->x);
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curve25519_add(b, p->y, p->x);
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curve25519_mul(a, a, qb[signbit]); /* ysubx for +, xaddy for - */
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curve25519_mul(r->x, b, qb[signbit^1]); /* xaddy for +, ysubx for - */
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curve25519_add(r->y, r->x, a);
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curve25519_sub(r->x, r->x, a);
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curve25519_mul(c, p->t, q->t2d);
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curve25519_mul(r->t, p->z, q->z);
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curve25519_add_reduce(r->t, r->t, r->t);
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curve25519_copy(r->z, r->t);
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curve25519_add(rb[2+signbit], rb[2+signbit], c); /* z for +, t for - */
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curve25519_sub(rb[2+(signbit^1)], rb[2+(signbit^1)], c); /* t for +, z for - */
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}
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static void
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ge25519_double_partial(ge25519 *r, const ge25519 *p) {
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ge25519_p1p1 t;
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ge25519_double_p1p1(&t, p);
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ge25519_p1p1_to_partial(r, &t);
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}
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static void
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ge25519_double(ge25519 *r, const ge25519 *p) {
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ge25519_p1p1 t;
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ge25519_double_p1p1(&t, p);
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ge25519_p1p1_to_full(r, &t);
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}
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static void
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ge25519_add(ge25519 *r, const ge25519 *p, const ge25519 *q) {
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ge25519_p1p1 t;
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ge25519_add_p1p1(&t, p, q);
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ge25519_p1p1_to_full(r, &t);
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}
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static void
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ge25519_nielsadd2(ge25519 *r, const ge25519_niels *q) {
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bignum25519 a,b,c,e,f,g,h;
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curve25519_sub(a, r->y, r->x);
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curve25519_add(b, r->y, r->x);
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curve25519_mul(a, a, q->ysubx);
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curve25519_mul(e, b, q->xaddy);
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curve25519_add(h, e, a);
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curve25519_sub(e, e, a);
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curve25519_mul(c, r->t, q->t2d);
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curve25519_add(f, r->z, r->z);
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curve25519_add_after_basic(g, f, c);
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curve25519_sub_after_basic(f, f, c);
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curve25519_mul(r->x, e, f);
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curve25519_mul(r->y, h, g);
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curve25519_mul(r->z, g, f);
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curve25519_mul(r->t, e, h);
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}
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static void
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ge25519_pnielsadd(ge25519_pniels *r, const ge25519 *p, const ge25519_pniels *q) {
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bignum25519 a,b,c,x,y,z,t;
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curve25519_sub(a, p->y, p->x);
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curve25519_add(b, p->y, p->x);
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curve25519_mul(a, a, q->ysubx);
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curve25519_mul(x, b, q->xaddy);
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curve25519_add(y, x, a);
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curve25519_sub(x, x, a);
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curve25519_mul(c, p->t, q->t2d);
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curve25519_mul(t, p->z, q->z);
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curve25519_add(t, t, t);
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curve25519_add_after_basic(z, t, c);
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curve25519_sub_after_basic(t, t, c);
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curve25519_mul(r->xaddy, x, t);
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curve25519_mul(r->ysubx, y, z);
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curve25519_mul(r->z, z, t);
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curve25519_mul(r->t2d, x, y);
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curve25519_copy(y, r->ysubx);
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curve25519_sub(r->ysubx, r->ysubx, r->xaddy);
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curve25519_add(r->xaddy, r->xaddy, y);
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curve25519_mul(r->t2d, r->t2d, ge25519_ec2d);
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}
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/*
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pack & unpack
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*/
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static void
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ge25519_pack(unsigned char r[32], const ge25519 *p) {
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bignum25519 tx, ty, zi;
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unsigned char parity[32];
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curve25519_recip(zi, p->z);
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curve25519_mul(tx, p->x, zi);
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curve25519_mul(ty, p->y, zi);
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curve25519_contract(r, ty);
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curve25519_contract(parity, tx);
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r[31] ^= ((parity[0] & 1) << 7);
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}
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static int
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ge25519_unpack_negative_vartime(ge25519 *r, const unsigned char p[32]) {
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static const unsigned char zero[32] = {0};
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static const bignum25519 one = {1};
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unsigned char parity = p[31] >> 7;
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unsigned char check[32];
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bignum25519 t, root, num, den, d3;
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curve25519_expand(r->y, p);
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curve25519_copy(r->z, one);
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curve25519_square(num, r->y); /* x = y^2 */
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curve25519_mul(den, num, ge25519_ecd); /* den = dy^2 */
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curve25519_sub_reduce(num, num, r->z); /* x = y^1 - 1 */
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curve25519_add(den, den, r->z); /* den = dy^2 + 1 */
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/* Computation of sqrt(num/den) */
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/* 1.: computation of num^((p-5)/8)*den^((7p-35)/8) = (num*den^7)^((p-5)/8) */
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curve25519_square(t, den);
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curve25519_mul(d3, t, den);
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curve25519_square(r->x, d3);
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curve25519_mul(r->x, r->x, den);
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curve25519_mul(r->x, r->x, num);
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curve25519_pow_two252m3(r->x, r->x);
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/* 2. computation of r->x = num * den^3 * (num*den^7)^((p-5)/8) */
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curve25519_mul(r->x, r->x, d3);
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curve25519_mul(r->x, r->x, num);
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/* 3. Check if either of the roots works: */
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curve25519_square(t, r->x);
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curve25519_mul(t, t, den);
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curve25519_sub_reduce(root, t, num);
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curve25519_contract(check, root);
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if (!ed25519_verify(check, zero, 32)) {
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curve25519_add_reduce(t, t, num);
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curve25519_contract(check, t);
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if (!ed25519_verify(check, zero, 32))
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return 0;
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curve25519_mul(r->x, r->x, ge25519_sqrtneg1);
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}
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curve25519_contract(check, r->x);
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if ((check[0] & 1) == parity) {
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curve25519_copy(t, r->x);
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curve25519_neg(r->x, t);
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}
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curve25519_mul(r->t, r->x, r->y);
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return 1;
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}
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/*
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scalarmults
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*/
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#define S1_SWINDOWSIZE 5
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#define S1_TABLE_SIZE (1<<(S1_SWINDOWSIZE-2))
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#define S2_SWINDOWSIZE 7
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#define S2_TABLE_SIZE (1<<(S2_SWINDOWSIZE-2))
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/* computes [s1]p1 + [s2]basepoint */
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static void
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ge25519_double_scalarmult_vartime(ge25519 *r, const ge25519 *p1, const bignum256modm s1, const bignum256modm s2) {
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signed char slide1[256], slide2[256];
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ge25519_pniels pre1[S1_TABLE_SIZE];
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ge25519 d1;
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ge25519_p1p1 t;
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int32_t i;
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contract256_slidingwindow_modm(slide1, s1, S1_SWINDOWSIZE);
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contract256_slidingwindow_modm(slide2, s2, S2_SWINDOWSIZE);
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ge25519_double(&d1, p1);
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ge25519_full_to_pniels(pre1, p1);
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for (i = 0; i < S1_TABLE_SIZE - 1; i++)
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ge25519_pnielsadd(&pre1[i+1], &d1, &pre1[i]);
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/* set neutral */
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memset(r, 0, sizeof(ge25519));
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r->y[0] = 1;
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r->z[0] = 1;
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i = 255;
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while ((i >= 0) && !(slide1[i] | slide2[i]))
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i--;
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for (; i >= 0; i--) {
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ge25519_double_p1p1(&t, r);
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if (slide1[i]) {
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ge25519_p1p1_to_full(r, &t);
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ge25519_pnielsadd_p1p1(&t, r, &pre1[abs(slide1[i]) / 2], (unsigned char)slide1[i] >> 7);
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}
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if (slide2[i]) {
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ge25519_p1p1_to_full(r, &t);
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ge25519_nielsadd2_p1p1(&t, r, &ge25519_niels_sliding_multiples[abs(slide2[i]) / 2], (unsigned char)slide2[i] >> 7);
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}
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ge25519_p1p1_to_partial(r, &t);
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}
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}
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#if !defined(HAVE_GE25519_SCALARMULT_BASE_CHOOSE_NIELS)
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static uint32_t
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ge25519_windowb_equal(uint32_t b, uint32_t c) {
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return ((b ^ c) - 1) >> 31;
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}
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static void
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ge25519_scalarmult_base_choose_niels(ge25519_niels *t, const uint8_t table[256][96], uint32_t pos, signed char b) {
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bignum25519 neg;
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uint32_t sign = (uint32_t)((unsigned char)b >> 7);
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uint32_t mask = ~(sign - 1);
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uint32_t u = (b + mask) ^ mask;
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uint32_t i;
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/* ysubx, xaddy, t2d in packed form. initialize to ysubx = 1, xaddy = 1, t2d = 0 */
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uint8_t packed[96] = {0};
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packed[0] = 1;
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packed[32] = 1;
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for (i = 0; i < 8; i++)
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curve25519_move_conditional_bytes(packed, table[(pos * 8) + i], ge25519_windowb_equal(u, i + 1));
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/* expand in to t */
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curve25519_expand(t->ysubx, packed + 0);
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curve25519_expand(t->xaddy, packed + 32);
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curve25519_expand(t->t2d , packed + 64);
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/* adjust for sign */
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curve25519_swap_conditional(t->ysubx, t->xaddy, sign);
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curve25519_neg(neg, t->t2d);
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curve25519_swap_conditional(t->t2d, neg, sign);
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}
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#endif /* HAVE_GE25519_SCALARMULT_BASE_CHOOSE_NIELS */
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/* computes [s]basepoint */
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static void
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ge25519_scalarmult_base_niels(ge25519 *r, const uint8_t basepoint_table[256][96], const bignum256modm s) {
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signed char b[64];
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uint32_t i;
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ge25519_niels t;
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contract256_window4_modm(b, s);
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ge25519_scalarmult_base_choose_niels(&t, basepoint_table, 0, b[1]);
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curve25519_sub_reduce(r->x, t.xaddy, t.ysubx);
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curve25519_add_reduce(r->y, t.xaddy, t.ysubx);
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memset(r->z, 0, sizeof(bignum25519));
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curve25519_copy(r->t, t.t2d);
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r->z[0] = 2;
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for (i = 3; i < 64; i += 2) {
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ge25519_scalarmult_base_choose_niels(&t, basepoint_table, i / 2, b[i]);
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ge25519_nielsadd2(r, &t);
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}
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ge25519_double_partial(r, r);
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ge25519_double_partial(r, r);
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ge25519_double_partial(r, r);
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ge25519_double(r, r);
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ge25519_scalarmult_base_choose_niels(&t, basepoint_table, 0, b[0]);
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curve25519_mul(t.t2d, t.t2d, ge25519_ecd);
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ge25519_nielsadd2(r, &t);
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for(i = 2; i < 64; i += 2) {
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ge25519_scalarmult_base_choose_niels(&t, basepoint_table, i / 2, b[i]);
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ge25519_nielsadd2(r, &t);
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}
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}
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