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/*
* ecgen, tool for generating Elliptic curve domain parameters
* Copyright (C) 2017-2018 J08nY
*/
#include "ansi.h"
#include "gen/field.h"
#include "gen/seed.h"
#include "io/output.h"
#include "util/bits.h"
#include "util/memory.h"
#include "util/str.h"
static seed_t *ansi_new() {
seed_t *result = seed_new();
result->type = SEED_ANSI;
return result;
}
bool ansi_seed_valid(const char *hex_str) {
const char *seed = str_is_hex(hex_str);
return seed && strlen(seed) >= 40;
}
static void seed_hash(seed_t *seed) {
seed->hash20 = try_malloc(20);
bits_sha1(seed->seed, seed->hash20);
}
static void seed_tsh(seed_t *seed) {
pari_sp ltop = avma;
seed->ansi.t = utoi(cfg->bits);
seed->ansi.s =
floorr(rdivii(subis(seed->ansi.t, 1), stoi(160), DEFAULTPREC));
seed->ansi.h = subii(seed->ansi.t, mulis(seed->ansi.s, 160));
gerepileall(ltop, 3, &seed->ansi.t, &seed->ansi.s, &seed->ansi.h);
}
GENERATOR(ansi_gen_seed_random) {
seed_t *seed = ansi_new();
seed->seed = bits_from_i(random_int(160));
seed_hash(seed);
seed_tsh(seed);
curve->seed = seed;
return 1;
}
GENERATOR(ansi_gen_seed_argument) {
seed_t *seed = ansi_new();
seed->seed = bits_from_hex(str_is_hex(cfg->seed));
seed_hash(seed);
seed_tsh(seed);
curve->seed = seed;
return 1;
}
GENERATOR(ansi_gen_seed_input) {
pari_sp ltop = avma;
GEN str = input_string("seed:");
const char *cstr = GSTR(str);
if (!ansi_seed_valid(cstr)) {
fprintf(err, "SEED must be at least 160 bits(40 hex characters).\n");
avma = ltop;
return 0;
}
seed_t *seed = ansi_new();
seed->seed = bits_from_hex(str_is_hex(cstr));
seed_hash(seed);
seed_tsh(seed);
curve->seed = seed;
return 1;
}
static bits_t *seed_process(seed_t *seed, const bits_t *first) {
pari_sp ltop = avma;
bits_t *result = bits_copy(first);
long is = itos(seed->ansi.s);
GEN seedi = bits_to_i(seed->seed);
GEN two_g = int2n(seed->seed->bitlen);
for (long i = 1; i <= is; ++i) {
pari_sp btop = avma;
GEN inner = addis(seedi, i);
inner = modii(inner, two_g);
bits_t *to_hash = bits_from_i(inner);
if (to_hash->bitlen < seed->seed->bitlen) {
bits_lengthenz(to_hash, seed->seed->bitlen - to_hash->bitlen);
}
unsigned char hashout[20];
bits_sha1(to_hash, hashout);
bits_t *Wi = bits_from_raw(hashout, 160);
bits_concatz(result, Wi, NULL);
bits_free(&to_hash);
bits_free(&Wi);
avma = btop;
}
avma = ltop;
return result;
}
static GENERATOR(ansi_gen_equation_fp) {
pari_sp ltop = avma;
bits_t *c0 = bits_from_raw(curve->seed->hash20, 160);
bits_shortenz(c0, 160 - itos(curve->seed->ansi.h));
bits_t *W0 = bits_copy(c0);
SET_BIT(W0->bits, 0, 0);
bits_t *W = seed_process(curve->seed, W0);
long ti = itos(curve->seed->ansi.t);
GEN r = gen_0;
for (long i = 1; i <= ti; ++i) {
GEN Wi = stoi(GET_BIT(W->bits, i - 1));
r = addii(r, mulii(Wi, int2n(ti - i)));
}
curve->seed->ansi.r = r;
GEN r_inv = Fp_invsafe(r, curve->field);
GEN a;
GEN b2;
do {
a = random_int(cfg->bits);
b2 = mulii(powis(a, 3), r_inv);
} while (!Fp_issquare(b2, curve->field));
GEN b = Fp_sqrt(b2, curve->field);
curve->a = a;
curve->b = b;
gerepileall(ltop, 3, &curve->seed->ansi.r, &curve->a, &curve->b);
bits_free(&c0);
bits_free(&W0);
bits_free(&W);
return 1;
}
static GENERATOR(ansi_gen_equation_f2m) {
pari_sp ltop = avma;
bits_t *b0 = bits_from_raw(curve->seed->hash20, 160);
bits_shortenz(b0, 160 - itos(curve->seed->ansi.h));
bits_t *b = seed_process(curve->seed, b0);
GEN ib = bits_to_i(b);
if (gequal0(ib)) {
avma = ltop;
return -3;
}
GEN a = random_int(cfg->bits);
curve->a = field_ielement(curve->field, a);
curve->b = field_ielement(curve->field, ib);
gerepileall(ltop, 2, &curve->a, &curve->b);
bits_free(&b0);
bits_free(&b);
return 1;
}
GENERATOR(ansi_gen_equation) {
switch (cfg->field) {
case FIELD_PRIME:
return ansi_gen_equation_fp(curve, args, state);
case FIELD_BINARY:
return ansi_gen_equation_f2m(curve, args, state);
default:
pari_err_BUG("Field not prime or binary?");
return INT_MIN; /* NOT REACHABLE */
}
}
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