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pqc/crypto_kem/ntruhps2048677/clean/poly.c
Douglas Stebila 580b0d76e3 Add ntruhps2048677
2019-04-29 09:41:17 -04:00

346 řádky
10 KiB
C
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#include "poly.h"
#include "fips202.h"
#include "verify.h"
uint16_t PQCLEAN_NTRUHPS2048677_CLEAN_mod3(uint16_t a) {
uint16_t r;
int16_t t, c;
r = (a >> 8) + (a & 0xff); // r mod 255 == a mod 255
r = (r >> 4) + (r & 0xf); // r' mod 15 == r mod 15
r = (r >> 2) + (r & 0x3); // r' mod 3 == r mod 3
r = (r >> 2) + (r & 0x3); // r' mod 3 == r mod 3
t = r - 3;
c = t >> 15;
return (c & r) ^ (~c & t);
}
/* Map {0, 1, 2} -> {0,1,q-1} in place */
void PQCLEAN_NTRUHPS2048677_CLEAN_poly_Z3_to_Zq(poly *r) {
int i;
for (i = 0; i < NTRU_N; i++) {
r->coeffs[i] = r->coeffs[i] | ((-(r->coeffs[i] >> 1)) & (NTRU_Q - 1));
}
}
/* Map {0, 1, q-1} -> {0,1,2} in place */
void PQCLEAN_NTRUHPS2048677_CLEAN_poly_trinary_Zq_to_Z3(poly *r) {
int i;
for (i = 0; i < NTRU_N; i++) {
r->coeffs[i] = 3 & (r->coeffs[i] ^ (r->coeffs[i] >> (NTRU_LOGQ - 1)));
}
}
void PQCLEAN_NTRUHPS2048677_CLEAN_poly_Rq_mul(poly *r, const poly *a, const poly *b) {
int k, i;
for (k = 0; k < NTRU_N; k++) {
r->coeffs[k] = 0;
for (i = 1; i < NTRU_N - k; i++) {
r->coeffs[k] += a->coeffs[k + i] * b->coeffs[NTRU_N - i];
}
for (i = 0; i < k + 1; i++) {
r->coeffs[k] += a->coeffs[k - i] * b->coeffs[i];
}
r->coeffs[k] = MODQ(r->coeffs[k]);
}
}
void PQCLEAN_NTRUHPS2048677_CLEAN_poly_Sq_mul(poly *r, const poly *a, const poly *b) {
int i;
PQCLEAN_NTRUHPS2048677_CLEAN_poly_Rq_mul(r, a, b);
for (i = 0; i < NTRU_N; i++) {
r->coeffs[i] = MODQ(r->coeffs[i] - r->coeffs[NTRU_N - 1]);
}
}
void PQCLEAN_NTRUHPS2048677_CLEAN_poly_S3_mul(poly *r, const poly *a, const poly *b) {
int k, i;
for (k = 0; k < NTRU_N; k++) {
r->coeffs[k] = 0;
for (i = 1; i < NTRU_N - k; i++) {
r->coeffs[k] += a->coeffs[k + i] * b->coeffs[NTRU_N - i];
}
for (i = 0; i < k + 1; i++) {
r->coeffs[k] += a->coeffs[k - i] * b->coeffs[i];
}
}
for (k = 0; k < NTRU_N; k++) {
r->coeffs[k] = PQCLEAN_NTRUHPS2048677_CLEAN_mod3(r->coeffs[k] + 2 * r->coeffs[NTRU_N - 1]);
}
}
void PQCLEAN_NTRUHPS2048677_CLEAN_poly_Rq_mul_x_minus_1(poly *r, const poly *a) {
int i;
uint16_t last_coeff = a->coeffs[NTRU_N - 1];
for (i = NTRU_N - 1; i > 0; i--) {
r->coeffs[i] = MODQ(a->coeffs[i - 1] + (NTRU_Q - a->coeffs[i]));
}
r->coeffs[0] = MODQ(last_coeff + (NTRU_Q - a->coeffs[0]));
}
void PQCLEAN_NTRUHPS2048677_CLEAN_poly_lift(poly *r, const poly *a) {
int i;
for (i = 0; i < NTRU_N; i++) {
r->coeffs[i] = a->coeffs[i];
}
PQCLEAN_NTRUHPS2048677_CLEAN_poly_Z3_to_Zq(r);
}
void PQCLEAN_NTRUHPS2048677_CLEAN_poly_Rq_to_S3(poly *r, const poly *a) {
/* NOTE: Assumes input is in [0,Q-1]^N */
/* Produces output in {0,1,2}^N */
int i;
/* Center coeffs around 3Q: [0, Q-1] -> [3Q - Q/2, 3Q + Q/2) */
for (i = 0; i < NTRU_N; i++) {
r->coeffs[i] = ((a->coeffs[i] >> (NTRU_LOGQ - 1)) ^ 3) << NTRU_LOGQ;
r->coeffs[i] += a->coeffs[i];
}
/* Reduce mod (3, Phi) */
r->coeffs[NTRU_N - 1] = PQCLEAN_NTRUHPS2048677_CLEAN_mod3(r->coeffs[NTRU_N - 1]);
for (i = 0; i < NTRU_N; i++) {
r->coeffs[i] = PQCLEAN_NTRUHPS2048677_CLEAN_mod3(r->coeffs[i] + 2 * r->coeffs[NTRU_N - 1]);
}
}
#define POLY_R2_ADD(I,A,B,S) \
for ((I)=0; (I)<NTRU_N; (I)++) { \
(A).coeffs[(I)] ^= (B).coeffs[(I)] * (S); \
}
static void cswappoly(poly *a, poly *b, int swap) {
int i;
uint16_t t;
swap = -swap;
for (i = 0; i < NTRU_N; i++) {
t = (a->coeffs[i] ^ b->coeffs[i]) & swap;
a->coeffs[i] ^= t;
b->coeffs[i] ^= t;
}
}
static inline void poly_divx(poly *a, int s) {
int i;
for (i = 1; i < NTRU_N; i++) {
a->coeffs[i - 1] = (unsigned char) ((s * a->coeffs[i]) | (!s * a->coeffs[i - 1]));
}
a->coeffs[NTRU_N - 1] = (!s * a->coeffs[NTRU_N - 1]);
}
static inline void poly_mulx(poly *a, int s) {
int i;
for (i = 1; i < NTRU_N; i++) {
a->coeffs[NTRU_N - i] = (unsigned char) ((s * a->coeffs[NTRU_N - i - 1]) | (!s * a->coeffs[NTRU_N - i]));
}
a->coeffs[0] = (!s * a->coeffs[0]);
}
static void poly_R2_inv(poly *r, const poly *a) {
/* Schroeppel--Orman--O'Malley--Spatscheck
* "Almost Inverse" algorithm as described
* by Silverman in NTRU Tech Report #14 */
// with several modifications to make it run in constant-time
int i, j;
int k = 0;
uint16_t degf = NTRU_N - 1;
uint16_t degg = NTRU_N - 1;
int sign, t, swap;
int16_t done = 0;
poly b, f, g;
poly *c = r; // save some stack space
poly *temp_r = &f;
/* b(X) := 1 */
for (i = 1; i < NTRU_N; i++) {
b.coeffs[i] = 0;
}
b.coeffs[0] = 1;
/* c(X) := 0 */
for (i = 0; i < NTRU_N; i++) {
c->coeffs[i] = 0;
}
/* f(X) := a(X) */
for (i = 0; i < NTRU_N; i++) {
f.coeffs[i] = a->coeffs[i] & 1;
}
/* g(X) := 1 + X + X^2 + ... + X^{N-1} */
for (i = 0; i < NTRU_N; i++) {
g.coeffs[i] = 1;
}
for (j = 0; j < 2 * (NTRU_N - 1) - 1; j++) {
sign = f.coeffs[0];
swap = sign & !done & ((degf - degg) >> 15);
cswappoly(&f, &g, swap);
cswappoly(&b, c, swap);
t = (degf ^ degg) & (-swap);
degf ^= t;
degg ^= t;
POLY_R2_ADD(i, f, g, sign * (!done));
POLY_R2_ADD(i, b, (*c), sign * (!done));
poly_divx(&f, !done);
poly_mulx(c, !done);
degf -= !done;
k += !done;
done = 1 - (((uint16_t) - degf) >> 15);
}
k = k - NTRU_N * ((uint16_t)(NTRU_N - k - 1) >> 15);
/* Return X^{N-k} * b(X) */
/* This is a k-coefficient rotation. We do this by looking at the binary
representation of k, rotating for every power of 2, and performing a cmov
if the respective bit is set. */
for (i = 0; i < NTRU_N; i++) {
r->coeffs[i] = b.coeffs[i];
}
for (i = 0; i < 10; i++) {
for (j = 0; j < NTRU_N; j++) {
temp_r->coeffs[j] = r->coeffs[(j + (1 << i)) % NTRU_N];
}
PQCLEAN_NTRUHPS2048677_CLEAN_cmov((unsigned char *) & (r->coeffs),
(unsigned char *) & (temp_r->coeffs), sizeof(uint16_t) * NTRU_N, k & 1);
k >>= 1;
}
}
static void poly_R2_inv_to_Rq_inv(poly *r, const poly *ai, const poly *a) {
int i;
poly b, c;
poly s;
// for 0..4
// ai = ai * (2 - a*ai) mod q
for (i = 0; i < NTRU_N; i++) {
b.coeffs[i] = MODQ(NTRU_Q - a->coeffs[i]); // b = -a
}
for (i = 0; i < NTRU_N; i++) {
r->coeffs[i] = ai->coeffs[i];
}
PQCLEAN_NTRUHPS2048677_CLEAN_poly_Rq_mul(&c, r, &b);
c.coeffs[0] += 2; // c = 2 - a*ai
PQCLEAN_NTRUHPS2048677_CLEAN_poly_Rq_mul(&s, &c, r); // s = ai*c
PQCLEAN_NTRUHPS2048677_CLEAN_poly_Rq_mul(&c, &s, &b);
c.coeffs[0] += 2; // c = 2 - a*s
PQCLEAN_NTRUHPS2048677_CLEAN_poly_Rq_mul(r, &c, &s); // r = s*c
PQCLEAN_NTRUHPS2048677_CLEAN_poly_Rq_mul(&c, r, &b);
c.coeffs[0] += 2; // c = 2 - a*r
PQCLEAN_NTRUHPS2048677_CLEAN_poly_Rq_mul(&s, &c, r); // s = r*c
PQCLEAN_NTRUHPS2048677_CLEAN_poly_Rq_mul(&c, &s, &b);
c.coeffs[0] += 2; // c = 2 - a*s
PQCLEAN_NTRUHPS2048677_CLEAN_poly_Rq_mul(r, &c, &s); // r = s*c
}
void PQCLEAN_NTRUHPS2048677_CLEAN_poly_Rq_inv(poly *r, const poly *a) {
poly ai2;
poly_R2_inv(&ai2, a);
poly_R2_inv_to_Rq_inv(r, &ai2, a);
}
void PQCLEAN_NTRUHPS2048677_CLEAN_poly_S3_inv(poly *r, const poly *a) {
/* Schroeppel--Orman--O'Malley--Spatscheck
* "Almost Inverse" algorithm as described
* by Silverman in NTRU Tech Report #14 */
// with several modifications to make it run in constant-time
int i, j;
uint16_t k = 0;
uint16_t degf = NTRU_N - 1;
uint16_t degg = NTRU_N - 1;
int sign, fsign = 0, t, swap;
int16_t done = 0;
poly b, c, f, g;
poly *temp_r = &f;
/* b(X) := 1 */
for (i = 1; i < NTRU_N; i++) {
b.coeffs[i] = 0;
}
b.coeffs[0] = 1;
/* c(X) := 0 */
for (i = 0; i < NTRU_N; i++) {
c.coeffs[i] = 0;
}
/* f(X) := a(X) */
for (i = 0; i < NTRU_N; i++) {
f.coeffs[i] = a->coeffs[i];
}
/* g(X) := 1 + X + X^2 + ... + X^{N-1} */
for (i = 0; i < NTRU_N; i++) {
g.coeffs[i] = 1;
}
for (j = 0; j < 2 * (NTRU_N - 1) - 1; j++) {
sign = PQCLEAN_NTRUHPS2048677_CLEAN_mod3(2 * g.coeffs[0] * f.coeffs[0]);
swap = (((sign & 2) >> 1) | sign) & !done & ((degf - degg) >> 15);
cswappoly(&f, &g, swap);
cswappoly(&b, &c, swap);
t = (degf ^ degg) & (-swap);
degf ^= t;
degg ^= t;
for (i = 0; i < NTRU_N; i++) {
f.coeffs[i] = PQCLEAN_NTRUHPS2048677_CLEAN_mod3(f.coeffs[i] + ((uint16_t) (sign * (!done))) * g.coeffs[i]);
}
for (i = 0; i < NTRU_N; i++) {
b.coeffs[i] = PQCLEAN_NTRUHPS2048677_CLEAN_mod3(b.coeffs[i] + ((uint16_t) (sign * (!done))) * c.coeffs[i]);
}
poly_divx(&f, !done);
poly_mulx(&c, !done);
degf -= !done;
k += !done;
done = 1 - (((uint16_t) - degf) >> 15);
}
fsign = f.coeffs[0];
k = k - NTRU_N * ((uint16_t)(NTRU_N - k - 1) >> 15);
/* Return X^{N-k} * b(X) */
/* This is a k-coefficient rotation. We do this by looking at the binary
representation of k, rotating for every power of 2, and performing a cmov
if the respective bit is set. */
for (i = 0; i < NTRU_N; i++) {
r->coeffs[i] = PQCLEAN_NTRUHPS2048677_CLEAN_mod3((uint16_t) fsign * b.coeffs[i]);
}
for (i = 0; i < 10; i++) {
for (j = 0; j < NTRU_N; j++) {
temp_r->coeffs[j] = r->coeffs[(j + (1 << i)) % NTRU_N];
}
PQCLEAN_NTRUHPS2048677_CLEAN_cmov((unsigned char *) & (r->coeffs),
(unsigned char *) & (temp_r->coeffs), sizeof(uint16_t) * NTRU_N, k & 1);
k >>= 1;
}
/* Reduce modulo Phi_n */
for (i = 0; i < NTRU_N; i++) {
r->coeffs[i] = PQCLEAN_NTRUHPS2048677_CLEAN_mod3(r->coeffs[i] + 2 * r->coeffs[NTRU_N - 1]);
}
}
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