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-rw-r--r--crypto/secp256k1/libsecp256k1/src/group_impl.h632
1 files changed, 632 insertions, 0 deletions
diff --git a/crypto/secp256k1/libsecp256k1/src/group_impl.h b/crypto/secp256k1/libsecp256k1/src/group_impl.h
new file mode 100644
index 000000000..fe0a35929
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+++ b/crypto/secp256k1/libsecp256k1/src/group_impl.h
@@ -0,0 +1,632 @@
+/**********************************************************************
+ * Copyright (c) 2013, 2014 Pieter Wuille *
+ * Distributed under the MIT software license, see the accompanying *
+ * file COPYING or http://www.opensource.org/licenses/mit-license.php.*
+ **********************************************************************/
+
+#ifndef _SECP256K1_GROUP_IMPL_H_
+#define _SECP256K1_GROUP_IMPL_H_
+
+#include <string.h>
+
+#include "num.h"
+#include "field.h"
+#include "group.h"
+
+/** Generator for secp256k1, value 'g' defined in
+ * "Standards for Efficient Cryptography" (SEC2) 2.7.1.
+ */
+static const secp256k1_ge secp256k1_ge_const_g = SECP256K1_GE_CONST(
+ 0x79BE667EUL, 0xF9DCBBACUL, 0x55A06295UL, 0xCE870B07UL,
+ 0x029BFCDBUL, 0x2DCE28D9UL, 0x59F2815BUL, 0x16F81798UL,
+ 0x483ADA77UL, 0x26A3C465UL, 0x5DA4FBFCUL, 0x0E1108A8UL,
+ 0xFD17B448UL, 0xA6855419UL, 0x9C47D08FUL, 0xFB10D4B8UL
+);
+
+static void secp256k1_ge_set_gej_zinv(secp256k1_ge *r, const secp256k1_gej *a, const secp256k1_fe *zi) {
+ secp256k1_fe zi2;
+ secp256k1_fe zi3;
+ secp256k1_fe_sqr(&zi2, zi);
+ secp256k1_fe_mul(&zi3, &zi2, zi);
+ secp256k1_fe_mul(&r->x, &a->x, &zi2);
+ secp256k1_fe_mul(&r->y, &a->y, &zi3);
+ r->infinity = a->infinity;
+}
+
+static void secp256k1_ge_set_infinity(secp256k1_ge *r) {
+ r->infinity = 1;
+}
+
+static void secp256k1_ge_set_xy(secp256k1_ge *r, const secp256k1_fe *x, const secp256k1_fe *y) {
+ r->infinity = 0;
+ r->x = *x;
+ r->y = *y;
+}
+
+static int secp256k1_ge_is_infinity(const secp256k1_ge *a) {
+ return a->infinity;
+}
+
+static void secp256k1_ge_neg(secp256k1_ge *r, const secp256k1_ge *a) {
+ *r = *a;
+ secp256k1_fe_normalize_weak(&r->y);
+ secp256k1_fe_negate(&r->y, &r->y, 1);
+}
+
+static void secp256k1_ge_set_gej(secp256k1_ge *r, secp256k1_gej *a) {
+ secp256k1_fe z2, z3;
+ r->infinity = a->infinity;
+ secp256k1_fe_inv(&a->z, &a->z);
+ secp256k1_fe_sqr(&z2, &a->z);
+ secp256k1_fe_mul(&z3, &a->z, &z2);
+ secp256k1_fe_mul(&a->x, &a->x, &z2);
+ secp256k1_fe_mul(&a->y, &a->y, &z3);
+ secp256k1_fe_set_int(&a->z, 1);
+ r->x = a->x;
+ r->y = a->y;
+}
+
+static void secp256k1_ge_set_gej_var(secp256k1_ge *r, secp256k1_gej *a) {
+ secp256k1_fe z2, z3;
+ r->infinity = a->infinity;
+ if (a->infinity) {
+ return;
+ }
+ secp256k1_fe_inv_var(&a->z, &a->z);
+ secp256k1_fe_sqr(&z2, &a->z);
+ secp256k1_fe_mul(&z3, &a->z, &z2);
+ secp256k1_fe_mul(&a->x, &a->x, &z2);
+ secp256k1_fe_mul(&a->y, &a->y, &z3);
+ secp256k1_fe_set_int(&a->z, 1);
+ r->x = a->x;
+ r->y = a->y;
+}
+
+static void secp256k1_ge_set_all_gej_var(size_t len, secp256k1_ge *r, const secp256k1_gej *a, const secp256k1_callback *cb) {
+ secp256k1_fe *az;
+ secp256k1_fe *azi;
+ size_t i;
+ size_t count = 0;
+ az = (secp256k1_fe *)checked_malloc(cb, sizeof(secp256k1_fe) * len);
+ for (i = 0; i < len; i++) {
+ if (!a[i].infinity) {
+ az[count++] = a[i].z;
+ }
+ }
+
+ azi = (secp256k1_fe *)checked_malloc(cb, sizeof(secp256k1_fe) * count);
+ secp256k1_fe_inv_all_var(count, azi, az);
+ free(az);
+
+ count = 0;
+ for (i = 0; i < len; i++) {
+ r[i].infinity = a[i].infinity;
+ if (!a[i].infinity) {
+ secp256k1_ge_set_gej_zinv(&r[i], &a[i], &azi[count++]);
+ }
+ }
+ free(azi);
+}
+
+static void secp256k1_ge_set_table_gej_var(size_t len, secp256k1_ge *r, const secp256k1_gej *a, const secp256k1_fe *zr) {
+ size_t i = len - 1;
+ secp256k1_fe zi;
+
+ if (len > 0) {
+ /* Compute the inverse of the last z coordinate, and use it to compute the last affine output. */
+ secp256k1_fe_inv(&zi, &a[i].z);
+ secp256k1_ge_set_gej_zinv(&r[i], &a[i], &zi);
+
+ /* Work out way backwards, using the z-ratios to scale the x/y values. */
+ while (i > 0) {
+ secp256k1_fe_mul(&zi, &zi, &zr[i]);
+ i--;
+ secp256k1_ge_set_gej_zinv(&r[i], &a[i], &zi);
+ }
+ }
+}
+
+static void secp256k1_ge_globalz_set_table_gej(size_t len, secp256k1_ge *r, secp256k1_fe *globalz, const secp256k1_gej *a, const secp256k1_fe *zr) {
+ size_t i = len - 1;
+ secp256k1_fe zs;
+
+ if (len > 0) {
+ /* The z of the final point gives us the "global Z" for the table. */
+ r[i].x = a[i].x;
+ r[i].y = a[i].y;
+ *globalz = a[i].z;
+ r[i].infinity = 0;
+ zs = zr[i];
+
+ /* Work our way backwards, using the z-ratios to scale the x/y values. */
+ while (i > 0) {
+ if (i != len - 1) {
+ secp256k1_fe_mul(&zs, &zs, &zr[i]);
+ }
+ i--;
+ secp256k1_ge_set_gej_zinv(&r[i], &a[i], &zs);
+ }
+ }
+}
+
+static void secp256k1_gej_set_infinity(secp256k1_gej *r) {
+ r->infinity = 1;
+ secp256k1_fe_set_int(&r->x, 0);
+ secp256k1_fe_set_int(&r->y, 0);
+ secp256k1_fe_set_int(&r->z, 0);
+}
+
+static void secp256k1_gej_set_xy(secp256k1_gej *r, const secp256k1_fe *x, const secp256k1_fe *y) {
+ r->infinity = 0;
+ r->x = *x;
+ r->y = *y;
+ secp256k1_fe_set_int(&r->z, 1);
+}
+
+static void secp256k1_gej_clear(secp256k1_gej *r) {
+ r->infinity = 0;
+ secp256k1_fe_clear(&r->x);
+ secp256k1_fe_clear(&r->y);
+ secp256k1_fe_clear(&r->z);
+}
+
+static void secp256k1_ge_clear(secp256k1_ge *r) {
+ r->infinity = 0;
+ secp256k1_fe_clear(&r->x);
+ secp256k1_fe_clear(&r->y);
+}
+
+static int secp256k1_ge_set_xo_var(secp256k1_ge *r, const secp256k1_fe *x, int odd) {
+ secp256k1_fe x2, x3, c;
+ r->x = *x;
+ secp256k1_fe_sqr(&x2, x);
+ secp256k1_fe_mul(&x3, x, &x2);
+ r->infinity = 0;
+ secp256k1_fe_set_int(&c, 7);
+ secp256k1_fe_add(&c, &x3);
+ if (!secp256k1_fe_sqrt_var(&r->y, &c)) {
+ return 0;
+ }
+ secp256k1_fe_normalize_var(&r->y);
+ if (secp256k1_fe_is_odd(&r->y) != odd) {
+ secp256k1_fe_negate(&r->y, &r->y, 1);
+ }
+ return 1;
+}
+
+static void secp256k1_gej_set_ge(secp256k1_gej *r, const secp256k1_ge *a) {
+ r->infinity = a->infinity;
+ r->x = a->x;
+ r->y = a->y;
+ secp256k1_fe_set_int(&r->z, 1);
+}
+
+static int secp256k1_gej_eq_x_var(const secp256k1_fe *x, const secp256k1_gej *a) {
+ secp256k1_fe r, r2;
+ VERIFY_CHECK(!a->infinity);
+ secp256k1_fe_sqr(&r, &a->z); secp256k1_fe_mul(&r, &r, x);
+ r2 = a->x; secp256k1_fe_normalize_weak(&r2);
+ return secp256k1_fe_equal_var(&r, &r2);
+}
+
+static void secp256k1_gej_neg(secp256k1_gej *r, const secp256k1_gej *a) {
+ r->infinity = a->infinity;
+ r->x = a->x;
+ r->y = a->y;
+ r->z = a->z;
+ secp256k1_fe_normalize_weak(&r->y);
+ secp256k1_fe_negate(&r->y, &r->y, 1);
+}
+
+static int secp256k1_gej_is_infinity(const secp256k1_gej *a) {
+ return a->infinity;
+}
+
+static int secp256k1_gej_is_valid_var(const secp256k1_gej *a) {
+ secp256k1_fe y2, x3, z2, z6;
+ if (a->infinity) {
+ return 0;
+ }
+ /** y^2 = x^3 + 7
+ * (Y/Z^3)^2 = (X/Z^2)^3 + 7
+ * Y^2 / Z^6 = X^3 / Z^6 + 7
+ * Y^2 = X^3 + 7*Z^6
+ */
+ secp256k1_fe_sqr(&y2, &a->y);
+ secp256k1_fe_sqr(&x3, &a->x); secp256k1_fe_mul(&x3, &x3, &a->x);
+ secp256k1_fe_sqr(&z2, &a->z);
+ secp256k1_fe_sqr(&z6, &z2); secp256k1_fe_mul(&z6, &z6, &z2);
+ secp256k1_fe_mul_int(&z6, 7);
+ secp256k1_fe_add(&x3, &z6);
+ secp256k1_fe_normalize_weak(&x3);
+ return secp256k1_fe_equal_var(&y2, &x3);
+}
+
+static int secp256k1_ge_is_valid_var(const secp256k1_ge *a) {
+ secp256k1_fe y2, x3, c;
+ if (a->infinity) {
+ return 0;
+ }
+ /* y^2 = x^3 + 7 */
+ secp256k1_fe_sqr(&y2, &a->y);
+ secp256k1_fe_sqr(&x3, &a->x); secp256k1_fe_mul(&x3, &x3, &a->x);
+ secp256k1_fe_set_int(&c, 7);
+ secp256k1_fe_add(&x3, &c);
+ secp256k1_fe_normalize_weak(&x3);
+ return secp256k1_fe_equal_var(&y2, &x3);
+}
+
+static void secp256k1_gej_double_var(secp256k1_gej *r, const secp256k1_gej *a, secp256k1_fe *rzr) {
+ /* Operations: 3 mul, 4 sqr, 0 normalize, 12 mul_int/add/negate */
+ secp256k1_fe t1,t2,t3,t4;
+ /** For secp256k1, 2Q is infinity if and only if Q is infinity. This is because if 2Q = infinity,
+ * Q must equal -Q, or that Q.y == -(Q.y), or Q.y is 0. For a point on y^2 = x^3 + 7 to have
+ * y=0, x^3 must be -7 mod p. However, -7 has no cube root mod p.
+ */
+ r->infinity = a->infinity;
+ if (r->infinity) {
+ if (rzr != NULL) {
+ secp256k1_fe_set_int(rzr, 1);
+ }
+ return;
+ }
+
+ if (rzr != NULL) {
+ *rzr = a->y;
+ secp256k1_fe_normalize_weak(rzr);
+ secp256k1_fe_mul_int(rzr, 2);
+ }
+
+ secp256k1_fe_mul(&r->z, &a->z, &a->y);
+ secp256k1_fe_mul_int(&r->z, 2); /* Z' = 2*Y*Z (2) */
+ secp256k1_fe_sqr(&t1, &a->x);
+ secp256k1_fe_mul_int(&t1, 3); /* T1 = 3*X^2 (3) */
+ secp256k1_fe_sqr(&t2, &t1); /* T2 = 9*X^4 (1) */
+ secp256k1_fe_sqr(&t3, &a->y);
+ secp256k1_fe_mul_int(&t3, 2); /* T3 = 2*Y^2 (2) */
+ secp256k1_fe_sqr(&t4, &t3);
+ secp256k1_fe_mul_int(&t4, 2); /* T4 = 8*Y^4 (2) */
+ secp256k1_fe_mul(&t3, &t3, &a->x); /* T3 = 2*X*Y^2 (1) */
+ r->x = t3;
+ secp256k1_fe_mul_int(&r->x, 4); /* X' = 8*X*Y^2 (4) */
+ secp256k1_fe_negate(&r->x, &r->x, 4); /* X' = -8*X*Y^2 (5) */
+ secp256k1_fe_add(&r->x, &t2); /* X' = 9*X^4 - 8*X*Y^2 (6) */
+ secp256k1_fe_negate(&t2, &t2, 1); /* T2 = -9*X^4 (2) */
+ secp256k1_fe_mul_int(&t3, 6); /* T3 = 12*X*Y^2 (6) */
+ secp256k1_fe_add(&t3, &t2); /* T3 = 12*X*Y^2 - 9*X^4 (8) */
+ secp256k1_fe_mul(&r->y, &t1, &t3); /* Y' = 36*X^3*Y^2 - 27*X^6 (1) */
+ secp256k1_fe_negate(&t2, &t4, 2); /* T2 = -8*Y^4 (3) */
+ secp256k1_fe_add(&r->y, &t2); /* Y' = 36*X^3*Y^2 - 27*X^6 - 8*Y^4 (4) */
+}
+
+static SECP256K1_INLINE void secp256k1_gej_double_nonzero(secp256k1_gej *r, const secp256k1_gej *a, secp256k1_fe *rzr) {
+ VERIFY_CHECK(!secp256k1_gej_is_infinity(a));
+ secp256k1_gej_double_var(r, a, rzr);
+}
+
+static void secp256k1_gej_add_var(secp256k1_gej *r, const secp256k1_gej *a, const secp256k1_gej *b, secp256k1_fe *rzr) {
+ /* Operations: 12 mul, 4 sqr, 2 normalize, 12 mul_int/add/negate */
+ secp256k1_fe z22, z12, u1, u2, s1, s2, h, i, i2, h2, h3, t;
+
+ if (a->infinity) {
+ VERIFY_CHECK(rzr == NULL);
+ *r = *b;
+ return;
+ }
+
+ if (b->infinity) {
+ if (rzr != NULL) {
+ secp256k1_fe_set_int(rzr, 1);
+ }
+ *r = *a;
+ return;
+ }
+
+ r->infinity = 0;
+ secp256k1_fe_sqr(&z22, &b->z);
+ secp256k1_fe_sqr(&z12, &a->z);
+ secp256k1_fe_mul(&u1, &a->x, &z22);
+ secp256k1_fe_mul(&u2, &b->x, &z12);
+ secp256k1_fe_mul(&s1, &a->y, &z22); secp256k1_fe_mul(&s1, &s1, &b->z);
+ secp256k1_fe_mul(&s2, &b->y, &z12); secp256k1_fe_mul(&s2, &s2, &a->z);
+ secp256k1_fe_negate(&h, &u1, 1); secp256k1_fe_add(&h, &u2);
+ secp256k1_fe_negate(&i, &s1, 1); secp256k1_fe_add(&i, &s2);
+ if (secp256k1_fe_normalizes_to_zero_var(&h)) {
+ if (secp256k1_fe_normalizes_to_zero_var(&i)) {
+ secp256k1_gej_double_var(r, a, rzr);
+ } else {
+ if (rzr != NULL) {
+ secp256k1_fe_set_int(rzr, 0);
+ }
+ r->infinity = 1;
+ }
+ return;
+ }
+ secp256k1_fe_sqr(&i2, &i);
+ secp256k1_fe_sqr(&h2, &h);
+ secp256k1_fe_mul(&h3, &h, &h2);
+ secp256k1_fe_mul(&h, &h, &b->z);
+ if (rzr != NULL) {
+ *rzr = h;
+ }
+ secp256k1_fe_mul(&r->z, &a->z, &h);
+ secp256k1_fe_mul(&t, &u1, &h2);
+ r->x = t; secp256k1_fe_mul_int(&r->x, 2); secp256k1_fe_add(&r->x, &h3); secp256k1_fe_negate(&r->x, &r->x, 3); secp256k1_fe_add(&r->x, &i2);
+ secp256k1_fe_negate(&r->y, &r->x, 5); secp256k1_fe_add(&r->y, &t); secp256k1_fe_mul(&r->y, &r->y, &i);
+ secp256k1_fe_mul(&h3, &h3, &s1); secp256k1_fe_negate(&h3, &h3, 1);
+ secp256k1_fe_add(&r->y, &h3);
+}
+
+static void secp256k1_gej_add_ge_var(secp256k1_gej *r, const secp256k1_gej *a, const secp256k1_ge *b, secp256k1_fe *rzr) {
+ /* 8 mul, 3 sqr, 4 normalize, 12 mul_int/add/negate */
+ secp256k1_fe z12, u1, u2, s1, s2, h, i, i2, h2, h3, t;
+ if (a->infinity) {
+ VERIFY_CHECK(rzr == NULL);
+ secp256k1_gej_set_ge(r, b);
+ return;
+ }
+ if (b->infinity) {
+ if (rzr != NULL) {
+ secp256k1_fe_set_int(rzr, 1);
+ }
+ *r = *a;
+ return;
+ }
+ r->infinity = 0;
+
+ secp256k1_fe_sqr(&z12, &a->z);
+ u1 = a->x; secp256k1_fe_normalize_weak(&u1);
+ secp256k1_fe_mul(&u2, &b->x, &z12);
+ s1 = a->y; secp256k1_fe_normalize_weak(&s1);
+ secp256k1_fe_mul(&s2, &b->y, &z12); secp256k1_fe_mul(&s2, &s2, &a->z);
+ secp256k1_fe_negate(&h, &u1, 1); secp256k1_fe_add(&h, &u2);
+ secp256k1_fe_negate(&i, &s1, 1); secp256k1_fe_add(&i, &s2);
+ if (secp256k1_fe_normalizes_to_zero_var(&h)) {
+ if (secp256k1_fe_normalizes_to_zero_var(&i)) {
+ secp256k1_gej_double_var(r, a, rzr);
+ } else {
+ if (rzr != NULL) {
+ secp256k1_fe_set_int(rzr, 0);
+ }
+ r->infinity = 1;
+ }
+ return;
+ }
+ secp256k1_fe_sqr(&i2, &i);
+ secp256k1_fe_sqr(&h2, &h);
+ secp256k1_fe_mul(&h3, &h, &h2);
+ if (rzr != NULL) {
+ *rzr = h;
+ }
+ secp256k1_fe_mul(&r->z, &a->z, &h);
+ secp256k1_fe_mul(&t, &u1, &h2);
+ r->x = t; secp256k1_fe_mul_int(&r->x, 2); secp256k1_fe_add(&r->x, &h3); secp256k1_fe_negate(&r->x, &r->x, 3); secp256k1_fe_add(&r->x, &i2);
+ secp256k1_fe_negate(&r->y, &r->x, 5); secp256k1_fe_add(&r->y, &t); secp256k1_fe_mul(&r->y, &r->y, &i);
+ secp256k1_fe_mul(&h3, &h3, &s1); secp256k1_fe_negate(&h3, &h3, 1);
+ secp256k1_fe_add(&r->y, &h3);
+}
+
+static void secp256k1_gej_add_zinv_var(secp256k1_gej *r, const secp256k1_gej *a, const secp256k1_ge *b, const secp256k1_fe *bzinv) {
+ /* 9 mul, 3 sqr, 4 normalize, 12 mul_int/add/negate */
+ secp256k1_fe az, z12, u1, u2, s1, s2, h, i, i2, h2, h3, t;
+
+ if (b->infinity) {
+ *r = *a;
+ return;
+ }
+ if (a->infinity) {
+ secp256k1_fe bzinv2, bzinv3;
+ r->infinity = b->infinity;
+ secp256k1_fe_sqr(&bzinv2, bzinv);
+ secp256k1_fe_mul(&bzinv3, &bzinv2, bzinv);
+ secp256k1_fe_mul(&r->x, &b->x, &bzinv2);
+ secp256k1_fe_mul(&r->y, &b->y, &bzinv3);
+ secp256k1_fe_set_int(&r->z, 1);
+ return;
+ }
+ r->infinity = 0;
+
+ /** We need to calculate (rx,ry,rz) = (ax,ay,az) + (bx,by,1/bzinv). Due to
+ * secp256k1's isomorphism we can multiply the Z coordinates on both sides
+ * by bzinv, and get: (rx,ry,rz*bzinv) = (ax,ay,az*bzinv) + (bx,by,1).
+ * This means that (rx,ry,rz) can be calculated as
+ * (ax,ay,az*bzinv) + (bx,by,1), when not applying the bzinv factor to rz.
+ * The variable az below holds the modified Z coordinate for a, which is used
+ * for the computation of rx and ry, but not for rz.
+ */
+ secp256k1_fe_mul(&az, &a->z, bzinv);
+
+ secp256k1_fe_sqr(&z12, &az);
+ u1 = a->x; secp256k1_fe_normalize_weak(&u1);
+ secp256k1_fe_mul(&u2, &b->x, &z12);
+ s1 = a->y; secp256k1_fe_normalize_weak(&s1);
+ secp256k1_fe_mul(&s2, &b->y, &z12); secp256k1_fe_mul(&s2, &s2, &az);
+ secp256k1_fe_negate(&h, &u1, 1); secp256k1_fe_add(&h, &u2);
+ secp256k1_fe_negate(&i, &s1, 1); secp256k1_fe_add(&i, &s2);
+ if (secp256k1_fe_normalizes_to_zero_var(&h)) {
+ if (secp256k1_fe_normalizes_to_zero_var(&i)) {
+ secp256k1_gej_double_var(r, a, NULL);
+ } else {
+ r->infinity = 1;
+ }
+ return;
+ }
+ secp256k1_fe_sqr(&i2, &i);
+ secp256k1_fe_sqr(&h2, &h);
+ secp256k1_fe_mul(&h3, &h, &h2);
+ r->z = a->z; secp256k1_fe_mul(&r->z, &r->z, &h);
+ secp256k1_fe_mul(&t, &u1, &h2);
+ r->x = t; secp256k1_fe_mul_int(&r->x, 2); secp256k1_fe_add(&r->x, &h3); secp256k1_fe_negate(&r->x, &r->x, 3); secp256k1_fe_add(&r->x, &i2);
+ secp256k1_fe_negate(&r->y, &r->x, 5); secp256k1_fe_add(&r->y, &t); secp256k1_fe_mul(&r->y, &r->y, &i);
+ secp256k1_fe_mul(&h3, &h3, &s1); secp256k1_fe_negate(&h3, &h3, 1);
+ secp256k1_fe_add(&r->y, &h3);
+}
+
+
+static void secp256k1_gej_add_ge(secp256k1_gej *r, const secp256k1_gej *a, const secp256k1_ge *b) {
+ /* Operations: 7 mul, 5 sqr, 4 normalize, 21 mul_int/add/negate/cmov */
+ static const secp256k1_fe fe_1 = SECP256K1_FE_CONST(0, 0, 0, 0, 0, 0, 0, 1);
+ secp256k1_fe zz, u1, u2, s1, s2, t, tt, m, n, q, rr;
+ secp256k1_fe m_alt, rr_alt;
+ int infinity, degenerate;
+ VERIFY_CHECK(!b->infinity);
+ VERIFY_CHECK(a->infinity == 0 || a->infinity == 1);
+
+ /** In:
+ * Eric Brier and Marc Joye, Weierstrass Elliptic Curves and Side-Channel Attacks.
+ * In D. Naccache and P. Paillier, Eds., Public Key Cryptography, vol. 2274 of Lecture Notes in Computer Science, pages 335-345. Springer-Verlag, 2002.
+ * we find as solution for a unified addition/doubling formula:
+ * lambda = ((x1 + x2)^2 - x1 * x2 + a) / (y1 + y2), with a = 0 for secp256k1's curve equation.
+ * x3 = lambda^2 - (x1 + x2)
+ * 2*y3 = lambda * (x1 + x2 - 2 * x3) - (y1 + y2).
+ *
+ * Substituting x_i = Xi / Zi^2 and yi = Yi / Zi^3, for i=1,2,3, gives:
+ * U1 = X1*Z2^2, U2 = X2*Z1^2
+ * S1 = Y1*Z2^3, S2 = Y2*Z1^3
+ * Z = Z1*Z2
+ * T = U1+U2
+ * M = S1+S2
+ * Q = T*M^2
+ * R = T^2-U1*U2
+ * X3 = 4*(R^2-Q)
+ * Y3 = 4*(R*(3*Q-2*R^2)-M^4)
+ * Z3 = 2*M*Z
+ * (Note that the paper uses xi = Xi / Zi and yi = Yi / Zi instead.)
+ *
+ * This formula has the benefit of being the same for both addition
+ * of distinct points and doubling. However, it breaks down in the
+ * case that either point is infinity, or that y1 = -y2. We handle
+ * these cases in the following ways:
+ *
+ * - If b is infinity we simply bail by means of a VERIFY_CHECK.
+ *
+ * - If a is infinity, we detect this, and at the end of the
+ * computation replace the result (which will be meaningless,
+ * but we compute to be constant-time) with b.x : b.y : 1.
+ *
+ * - If a = -b, we have y1 = -y2, which is a degenerate case.
+ * But here the answer is infinity, so we simply set the
+ * infinity flag of the result, overriding the computed values
+ * without even needing to cmov.
+ *
+ * - If y1 = -y2 but x1 != x2, which does occur thanks to certain
+ * properties of our curve (specifically, 1 has nontrivial cube
+ * roots in our field, and the curve equation has no x coefficient)
+ * then the answer is not infinity but also not given by the above
+ * equation. In this case, we cmov in place an alternate expression
+ * for lambda. Specifically (y1 - y2)/(x1 - x2). Where both these
+ * expressions for lambda are defined, they are equal, and can be
+ * obtained from each other by multiplication by (y1 + y2)/(y1 + y2)
+ * then substitution of x^3 + 7 for y^2 (using the curve equation).
+ * For all pairs of nonzero points (a, b) at least one is defined,
+ * so this covers everything.
+ */
+
+ secp256k1_fe_sqr(&zz, &a->z); /* z = Z1^2 */
+ u1 = a->x; secp256k1_fe_normalize_weak(&u1); /* u1 = U1 = X1*Z2^2 (1) */
+ secp256k1_fe_mul(&u2, &b->x, &zz); /* u2 = U2 = X2*Z1^2 (1) */
+ s1 = a->y; secp256k1_fe_normalize_weak(&s1); /* s1 = S1 = Y1*Z2^3 (1) */
+ secp256k1_fe_mul(&s2, &b->y, &zz); /* s2 = Y2*Z1^2 (1) */
+ secp256k1_fe_mul(&s2, &s2, &a->z); /* s2 = S2 = Y2*Z1^3 (1) */
+ t = u1; secp256k1_fe_add(&t, &u2); /* t = T = U1+U2 (2) */
+ m = s1; secp256k1_fe_add(&m, &s2); /* m = M = S1+S2 (2) */
+ secp256k1_fe_sqr(&rr, &t); /* rr = T^2 (1) */
+ secp256k1_fe_negate(&m_alt, &u2, 1); /* Malt = -X2*Z1^2 */
+ secp256k1_fe_mul(&tt, &u1, &m_alt); /* tt = -U1*U2 (2) */
+ secp256k1_fe_add(&rr, &tt); /* rr = R = T^2-U1*U2 (3) */
+ /** If lambda = R/M = 0/0 we have a problem (except in the "trivial"
+ * case that Z = z1z2 = 0, and this is special-cased later on). */
+ degenerate = secp256k1_fe_normalizes_to_zero(&m) &
+ secp256k1_fe_normalizes_to_zero(&rr);
+ /* This only occurs when y1 == -y2 and x1^3 == x2^3, but x1 != x2.
+ * This means either x1 == beta*x2 or beta*x1 == x2, where beta is
+ * a nontrivial cube root of one. In either case, an alternate
+ * non-indeterminate expression for lambda is (y1 - y2)/(x1 - x2),
+ * so we set R/M equal to this. */
+ rr_alt = s1;
+ secp256k1_fe_mul_int(&rr_alt, 2); /* rr = Y1*Z2^3 - Y2*Z1^3 (2) */
+ secp256k1_fe_add(&m_alt, &u1); /* Malt = X1*Z2^2 - X2*Z1^2 */
+
+ secp256k1_fe_cmov(&rr_alt, &rr, !degenerate);
+ secp256k1_fe_cmov(&m_alt, &m, !degenerate);
+ /* Now Ralt / Malt = lambda and is guaranteed not to be 0/0.
+ * From here on out Ralt and Malt represent the numerator
+ * and denominator of lambda; R and M represent the explicit
+ * expressions x1^2 + x2^2 + x1x2 and y1 + y2. */
+ secp256k1_fe_sqr(&n, &m_alt); /* n = Malt^2 (1) */
+ secp256k1_fe_mul(&q, &n, &t); /* q = Q = T*Malt^2 (1) */
+ /* These two lines use the observation that either M == Malt or M == 0,
+ * so M^3 * Malt is either Malt^4 (which is computed by squaring), or
+ * zero (which is "computed" by cmov). So the cost is one squaring
+ * versus two multiplications. */
+ secp256k1_fe_sqr(&n, &n);
+ secp256k1_fe_cmov(&n, &m, degenerate); /* n = M^3 * Malt (2) */
+ secp256k1_fe_sqr(&t, &rr_alt); /* t = Ralt^2 (1) */
+ secp256k1_fe_mul(&r->z, &a->z, &m_alt); /* r->z = Malt*Z (1) */
+ infinity = secp256k1_fe_normalizes_to_zero(&r->z) * (1 - a->infinity);
+ secp256k1_fe_mul_int(&r->z, 2); /* r->z = Z3 = 2*Malt*Z (2) */
+ secp256k1_fe_negate(&q, &q, 1); /* q = -Q (2) */
+ secp256k1_fe_add(&t, &q); /* t = Ralt^2-Q (3) */
+ secp256k1_fe_normalize_weak(&t);
+ r->x = t; /* r->x = Ralt^2-Q (1) */
+ secp256k1_fe_mul_int(&t, 2); /* t = 2*x3 (2) */
+ secp256k1_fe_add(&t, &q); /* t = 2*x3 - Q: (4) */
+ secp256k1_fe_mul(&t, &t, &rr_alt); /* t = Ralt*(2*x3 - Q) (1) */
+ secp256k1_fe_add(&t, &n); /* t = Ralt*(2*x3 - Q) + M^3*Malt (3) */
+ secp256k1_fe_negate(&r->y, &t, 3); /* r->y = Ralt*(Q - 2x3) - M^3*Malt (4) */
+ secp256k1_fe_normalize_weak(&r->y);
+ secp256k1_fe_mul_int(&r->x, 4); /* r->x = X3 = 4*(Ralt^2-Q) */
+ secp256k1_fe_mul_int(&r->y, 4); /* r->y = Y3 = 4*Ralt*(Q - 2x3) - 4*M^3*Malt (4) */
+
+ /** In case a->infinity == 1, replace r with (b->x, b->y, 1). */
+ secp256k1_fe_cmov(&r->x, &b->x, a->infinity);
+ secp256k1_fe_cmov(&r->y, &b->y, a->infinity);
+ secp256k1_fe_cmov(&r->z, &fe_1, a->infinity);
+ r->infinity = infinity;
+}
+
+static void secp256k1_gej_rescale(secp256k1_gej *r, const secp256k1_fe *s) {
+ /* Operations: 4 mul, 1 sqr */
+ secp256k1_fe zz;
+ VERIFY_CHECK(!secp256k1_fe_is_zero(s));
+ secp256k1_fe_sqr(&zz, s);
+ secp256k1_fe_mul(&r->x, &r->x, &zz); /* r->x *= s^2 */
+ secp256k1_fe_mul(&r->y, &r->y, &zz);
+ secp256k1_fe_mul(&r->y, &r->y, s); /* r->y *= s^3 */
+ secp256k1_fe_mul(&r->z, &r->z, s); /* r->z *= s */
+}
+
+static void secp256k1_ge_to_storage(secp256k1_ge_storage *r, const secp256k1_ge *a) {
+ secp256k1_fe x, y;
+ VERIFY_CHECK(!a->infinity);
+ x = a->x;
+ secp256k1_fe_normalize(&x);
+ y = a->y;
+ secp256k1_fe_normalize(&y);
+ secp256k1_fe_to_storage(&r->x, &x);
+ secp256k1_fe_to_storage(&r->y, &y);
+}
+
+static void secp256k1_ge_from_storage(secp256k1_ge *r, const secp256k1_ge_storage *a) {
+ secp256k1_fe_from_storage(&r->x, &a->x);
+ secp256k1_fe_from_storage(&r->y, &a->y);
+ r->infinity = 0;
+}
+
+static SECP256K1_INLINE void secp256k1_ge_storage_cmov(secp256k1_ge_storage *r, const secp256k1_ge_storage *a, int flag) {
+ secp256k1_fe_storage_cmov(&r->x, &a->x, flag);
+ secp256k1_fe_storage_cmov(&r->y, &a->y, flag);
+}
+
+#ifdef USE_ENDOMORPHISM
+static void secp256k1_ge_mul_lambda(secp256k1_ge *r, const secp256k1_ge *a) {
+ static const secp256k1_fe beta = SECP256K1_FE_CONST(
+ 0x7ae96a2bul, 0x657c0710ul, 0x6e64479eul, 0xac3434e9ul,
+ 0x9cf04975ul, 0x12f58995ul, 0xc1396c28ul, 0x719501eeul
+ );
+ *r = *a;
+ secp256k1_fe_mul(&r->x, &r->x, &beta);
+}
+#endif
+
+#endif
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