secp256k1/src/ecdsa.c

#include "num.h"
#include "field.h"
#include "group.h"
#include "ecmult.h"
#include "ecdsa.h"

void static secp256k1_ecdsa_sig_init(secp256k1_ecdsa_sig_t *r) {
    secp256k1_num_init(&r->r);
    secp256k1_num_init(&r->s);
}

void static secp256k1_ecdsa_sig_free(secp256k1_ecdsa_sig_t *r) {
    secp256k1_num_free(&r->r);
    secp256k1_num_free(&r->s);
}

int static secp256k1_ecdsa_pubkey_parse(secp256k1_gej_t *elem, const unsigned char *pub, int size) {
    if (size == 33 && (pub[0] == 0x02 || pub[0] == 0x03)) {
        secp256k1_fe_t x;
        secp256k1_fe_set_b32(&x, pub+1);
        secp256k1_gej_set_xo(elem, &x, pub[0] == 0x03);
    } else if (size == 65 && (pub[0] == 0x04 || pub[0] == 0x06 || pub[0] == 0x07)) {
        secp256k1_fe_t x, y;
        secp256k1_fe_set_b32(&x, pub+1);
        secp256k1_fe_set_b32(&y, pub+33);
        secp256k1_gej_set_xy(elem, &x, &y);
        if ((pub[0] == 0x06 || pub[0] == 0x07) && secp256k1_fe_is_odd(&y) != (pub[0] == 0x07))
            return 0;
    } else {
        return 0;
    }
    return secp256k1_gej_is_valid(elem);
}

int static secp256k1_ecdsa_sig_parse(secp256k1_ecdsa_sig_t *r, const unsigned char *sig, int size) {
    if (sig[0] != 0x30) return 0;
    int lenr = sig[3];
    if (5+lenr >= size) return 0;
    int lens = sig[lenr+5];
    if (sig[1] != lenr+lens+4) return 0;
    if (lenr+lens+6 > size) return 0;
    if (sig[2] != 0x02) return 0;
    if (lenr == 0) return 0;
    if (sig[lenr+4] != 0x02) return 0;
    if (lens == 0) return 0;
    secp256k1_num_set_bin(&r->r, sig+4, lenr);
    secp256k1_num_set_bin(&r->s, sig+6+lenr, lens);
    return 1;
}

int static secp256k1_ecdsa_sig_serialize(unsigned char *sig, int *size, const secp256k1_ecdsa_sig_t *a) {
    int lenR = (secp256k1_num_bits(&a->r) + 7)/8;
    if (lenR == 0 || secp256k1_num_get_bit(&a->r, lenR*8-1))
        lenR++;
    int lenS = (secp256k1_num_bits(&a->s) + 7)/8;
    if (lenS == 0 || secp256k1_num_get_bit(&a->s, lenS*8-1))
        lenS++;
    if (*size < 6+lenS+lenR)
        return 0;
    *size = 6 + lenS + lenR;
    sig[0] = 0x30;
    sig[1] = 4 + lenS + lenR;
    sig[2] = 0x02;
    sig[3] = lenR;
    secp256k1_num_get_bin(sig+4, lenR, &a->r);
    sig[4+lenR] = 0x02;
    sig[5+lenR] = lenS;
    secp256k1_num_get_bin(sig+lenR+6, lenS, &a->s);
    return 1;
}

int static secp256k1_ecdsa_sig_recompute(secp256k1_num_t *r2, const secp256k1_ecdsa_sig_t *sig, const secp256k1_gej_t *pubkey, const secp256k1_num_t *message) {
    const secp256k1_ge_consts_t *c = secp256k1_ge_consts;

    if (secp256k1_num_is_neg(&sig->r) || secp256k1_num_is_neg(&sig->s))
        return 0;
    if (secp256k1_num_is_zero(&sig->r) || secp256k1_num_is_zero(&sig->s))
        return 0;
    if (secp256k1_num_cmp(&sig->r, &c->order) >= 0 || secp256k1_num_cmp(&sig->s, &c->order) >= 0)
        return 0;

    int ret = 0;
    secp256k1_num_t sn, u1, u2;
    secp256k1_num_init(&sn);
    secp256k1_num_init(&u1);
    secp256k1_num_init(&u2);
    secp256k1_num_mod_inverse(&sn, &sig->s, &c->order);
    secp256k1_num_mod_mul(&u1, &sn, message, &c->order);
    secp256k1_num_mod_mul(&u2, &sn, &sig->r, &c->order);
    secp256k1_gej_t pr; secp256k1_ecmult(&pr, pubkey, &u2, &u1);
    if (!secp256k1_gej_is_infinity(&pr)) {
        secp256k1_fe_t xr; secp256k1_gej_get_x(&xr, &pr);
        secp256k1_fe_normalize(&xr);
        unsigned char xrb[32]; secp256k1_fe_get_b32(xrb, &xr);
        secp256k1_num_set_bin(r2, xrb, 32);
        secp256k1_num_mod(r2, r2, &c->order);
        ret = 1;
    }
    secp256k1_num_free(&sn);
    secp256k1_num_free(&u1);
    secp256k1_num_free(&u2);
    return ret;
}

int static secp256k1_ecdsa_sig_verify(const secp256k1_ecdsa_sig_t *sig, const secp256k1_gej_t *pubkey, const secp256k1_num_t *message) {
    secp256k1_num_t r2;
    secp256k1_num_init(&r2);
    int ret = 0;
    ret = secp256k1_ecdsa_sig_recompute(&r2, sig, pubkey, message) && secp256k1_num_cmp(&sig->r, &r2) == 0;
    secp256k1_num_free(&r2);
    return ret;
}

int static secp256k1_ecdsa_sig_sign(secp256k1_ecdsa_sig_t *sig, const secp256k1_num_t *seckey, const secp256k1_num_t *message, const secp256k1_num_t *nonce) {
    const secp256k1_ge_consts_t *c = secp256k1_ge_consts;

    secp256k1_gej_t rp;
    secp256k1_ecmult_gen(&rp, nonce);
    secp256k1_fe_t rx;
    secp256k1_gej_get_x(&rx, &rp);
    unsigned char b[32];
    secp256k1_fe_normalize(&rx);
    secp256k1_fe_get_b32(b, &rx);
    secp256k1_num_set_bin(&sig->r, b, 32);
    secp256k1_num_mod(&sig->r, &sig->r, &c->order);
    secp256k1_num_t n;
    secp256k1_num_init(&n);
    secp256k1_num_mod_mul(&n, &sig->r, seckey, &c->order);
    secp256k1_num_add(&n, &n, message);
    secp256k1_num_mod_inverse(&sig->s, nonce, &c->order);
    secp256k1_num_mod_mul(&sig->s, &sig->s, &n, &c->order);
    secp256k1_num_free(&n);
    if (secp256k1_num_is_zero(&sig->s))
        return 0;
    if (secp256k1_num_is_odd(&sig->s))
        secp256k1_num_sub(&sig->s, &c->order, &sig->s);
    return 1;
}

void static secp256k1_ecdsa_sig_set_rs(secp256k1_ecdsa_sig_t *sig, const secp256k1_num_t *r, const secp256k1_num_t *s) {
    secp256k1_num_copy(&sig->r, r);
    secp256k1_num_copy(&sig->s, s);
}