pqcrypto/crypto_kem/ntruhps2048509/clean/packq.c

#include "poly.h"

void PQCLEAN_NTRUHPS2048509_CLEAN_poly_Sq_tobytes(unsigned char *r, const poly *a) {
    int i, j;
    uint16_t t[8];

    for (i = 0; i < NTRU_PACK_DEG / 8; i++) {
        for (j = 0; j < 8; j++) {
            t[j] = MODQ(a->coeffs[8 * i + j]);
        }

        r[11 * i + 0] = (unsigned char) ( t[0]        & 0xff);
        r[11 * i + 1] = (unsigned char) ((t[0] >>  8) | ((t[1] & 0x1f) << 3));
        r[11 * i + 2] = (unsigned char) ((t[1] >>  5) | ((t[2] & 0x03) << 6));
        r[11 * i + 3] = (unsigned char) ((t[2] >>  2) & 0xff);
        r[11 * i + 4] = (unsigned char) ((t[2] >> 10) | ((t[3] & 0x7f) << 1));
        r[11 * i + 5] = (unsigned char) ((t[3] >>  7) | ((t[4] & 0x0f) << 4));
        r[11 * i + 6] = (unsigned char) ((t[4] >>  4) | ((t[5] & 0x01) << 7));
        r[11 * i + 7] = (unsigned char) ((t[5] >>  1) & 0xff);
        r[11 * i + 8] = (unsigned char) ((t[5] >>  9) | ((t[6] & 0x3f) << 2));
        r[11 * i + 9] = (unsigned char) ((t[6] >>  6) | ((t[7] & 0x07) << 5));
        r[11 * i + 10] = (unsigned char) ((t[7] >>  3));
    }

    for (j = 0; j < NTRU_PACK_DEG - 8 * i; j++) {
        t[j] = MODQ(a->coeffs[8 * i + j]);
    }
    for (; j < 8; j++) {
        t[j] = 0;
    }


    switch (NTRU_PACK_DEG & 0x07) {
    // cases 0 and 6 are impossible since 2 generates (Z/n)* and
    // p mod 8 in {1, 7} implies that 2 is a quadratic residue.
    case 4:
        r[11 * i + 0] = (unsigned char) (t[0]        & 0xff);
        r[11 * i + 1] = (unsigned char) (t[0] >>  8) | ((t[1] & 0x1f) << 3);
        r[11 * i + 2] = (unsigned char) (t[1] >>  5) | ((t[2] & 0x03) << 6);
        r[11 * i + 3] = (unsigned char) (t[2] >>  2) & 0xff;
        r[11 * i + 4] = (unsigned char) (t[2] >> 10) | ((t[3] & 0x7f) << 1);
        r[11 * i + 5] = (unsigned char) (t[3] >>  7) | ((t[4] & 0x0f) << 4);
        break;
    case 2:
        r[11 * i + 0] = (unsigned char) (t[0]        & 0xff);
        r[11 * i + 1] = (unsigned char) (t[0] >>  8) | ((t[1] & 0x1f) << 3);
        r[11 * i + 2] = (unsigned char) (t[1] >>  5) | ((t[2] & 0x03) << 6);
        break;
    }
}

void PQCLEAN_NTRUHPS2048509_CLEAN_poly_Sq_frombytes(poly *r, const unsigned char *a) {
    int i;
    for (i = 0; i < NTRU_PACK_DEG / 8; i++) {
        r->coeffs[8 * i + 0] = (a[11 * i + 0] >> 0) | (((uint16_t)a[11 * i + 1] & 0x07) << 8);
        r->coeffs[8 * i + 1] = (a[11 * i + 1] >> 3) | (((uint16_t)a[11 * i + 2] & 0x3f) << 5);
        r->coeffs[8 * i + 2] = (a[11 * i + 2] >> 6) | (((uint16_t)a[11 * i + 3] & 0xff) << 2) | (((uint16_t)a[11 * i + 4] & 0x01) << 10);
        r->coeffs[8 * i + 3] = (a[11 * i + 4] >> 1) | (((uint16_t)a[11 * i + 5] & 0x0f) << 7);
        r->coeffs[8 * i + 4] = (a[11 * i + 5] >> 4) | (((uint16_t)a[11 * i + 6] & 0x7f) << 4);
        r->coeffs[8 * i + 5] = (a[11 * i + 6] >> 7) | (((uint16_t)a[11 * i + 7] & 0xff) << 1) | (((uint16_t)a[11 * i + 8] & 0x03) <<  9);
        r->coeffs[8 * i + 6] = (a[11 * i + 8] >> 2) | (((uint16_t)a[11 * i + 9] & 0x1f) << 6);
        r->coeffs[8 * i + 7] = (a[11 * i + 9] >> 5) | (((uint16_t)a[11 * i + 10] & 0xff) << 3);
    }

    switch (NTRU_PACK_DEG & 0x07) {
    // cases 0 and 6 are impossible since 2 generates (Z/n)* and
    // p mod 8 in {1, 7} implies that 2 is a quadratic residue.
    case 4:
        r->coeffs[8 * i + 0] = (unsigned char) (a[11 * i + 0] >> 0) | (((uint16_t)a[11 * i + 1] & 0x07) << 8);
        r->coeffs[8 * i + 1] = (unsigned char) (a[11 * i + 1] >> 3) | (((uint16_t)a[11 * i + 2] & 0x3f) << 5);
        r->coeffs[8 * i + 2] = (unsigned char) (a[11 * i + 2] >> 6) | (((uint16_t)a[11 * i + 3] & 0xff) << 2) | (((uint16_t)a[11 * i + 4] & 0x01) << 10);
        r->coeffs[8 * i + 3] = (unsigned char) (a[11 * i + 4] >> 1) | (((uint16_t)a[11 * i + 5] & 0x0f) << 7);
        break;
    case 2:
        r->coeffs[8 * i + 0] = (unsigned char) (a[11 * i + 0] >> 0) | (((uint16_t)a[11 * i + 1] & 0x07) << 8);
        r->coeffs[8 * i + 1] = (unsigned char) (a[11 * i + 1] >> 3) | (((uint16_t)a[11 * i + 2] & 0x3f) << 5);
        break;
    }
    r->coeffs[NTRU_N - 1] = 0;
}

void PQCLEAN_NTRUHPS2048509_CLEAN_poly_Rq_sum_zero_tobytes(unsigned char *r, const poly *a) {
    PQCLEAN_NTRUHPS2048509_CLEAN_poly_Sq_tobytes(r, a);
}

void PQCLEAN_NTRUHPS2048509_CLEAN_poly_Rq_sum_zero_frombytes(poly *r, const unsigned char *a) {
    int i;
    PQCLEAN_NTRUHPS2048509_CLEAN_poly_Sq_frombytes(r, a);

    /* Set r[n-1] so that the sum of coefficients is zero mod q */
    r->coeffs[NTRU_N - 1] = 0;
    for (i = 0; i < NTRU_PACK_DEG; i++) {
        r->coeffs[NTRU_N - 1] -= r->coeffs[i];
    }
}