pqcrypto/crypto_kem/kyber768/clean/poly.c

#include "cbd.h"
#include "ntt.h"
#include "params.h"
#include "poly.h"
#include "reduce.h"
#include "symmetric.h"

#include <stdint.h>
/*************************************************
* Name:        poly_compress
*
* Description: Compression and subsequent serialization of a polynomial
*
* Arguments:   - uint8_t *r: pointer to output byte array (needs space for KYBER_POLYCOMPRESSEDBYTES bytes)
*              - const poly *a:    pointer to input polynomial
**************************************************/
void PQCLEAN_KYBER768_CLEAN_poly_compress(uint8_t *r, poly *a) {
    uint8_t t[8];
    size_t k = 0;

    PQCLEAN_KYBER768_CLEAN_poly_csubq(a);

    for (size_t i = 0; i < KYBER_N; i += 8) {
        for (size_t j = 0; j < 8; j++) {
            t[j] = ((((uint32_t)a->coeffs[i + j] << 4) + KYBER_Q / 2) / KYBER_Q) & 15;
        }

        r[k]     = (uint8_t)(t[0] | (t[1] << 4));
        r[k + 1] = (uint8_t)(t[2] | (t[3] << 4));
        r[k + 2] = (uint8_t)(t[4] | (t[5] << 4));
        r[k + 3] = (uint8_t)(t[6] | (t[7] << 4));
        k += 4;
    }
}

/*************************************************
* Name:        poly_decompress
*
* Description: De-serialization and subsequent decompression of a polynomial;
*              approximate inverse of poly_compress
*
* Arguments:   - poly *r:                pointer to output polynomial
*              - const uint8_t *a: pointer to input byte array (of length KYBER_POLYCOMPRESSEDBYTES bytes)
**************************************************/
void PQCLEAN_KYBER768_CLEAN_poly_decompress(poly *r, const uint8_t *a) {
    for (size_t i = 0; i < KYBER_N; i += 8) {
        r->coeffs[i + 0] = (int16_t)((((a[0] & 15) * KYBER_Q) + 8) >> 4);
        r->coeffs[i + 1] = (int16_t)((((a[0] >> 4) * KYBER_Q) + 8) >> 4);
        r->coeffs[i + 2] = (int16_t)((((a[1] & 15) * KYBER_Q) + 8) >> 4);
        r->coeffs[i + 3] = (int16_t)((((a[1] >> 4) * KYBER_Q) + 8) >> 4);
        r->coeffs[i + 4] = (int16_t)((((a[2] & 15) * KYBER_Q) + 8) >> 4);
        r->coeffs[i + 5] = (int16_t)((((a[2] >> 4) * KYBER_Q) + 8) >> 4);
        r->coeffs[i + 6] = (int16_t)((((a[3] & 15) * KYBER_Q) + 8) >> 4);
        r->coeffs[i + 7] = (int16_t)((((a[3] >> 4) * KYBER_Q) + 8) >> 4);
        a += 4;
    }
}

/*************************************************
* Name:        poly_tobytes
*
* Description: Serialization of a polynomial
*
* Arguments:   - uint8_t *r: pointer to output byte array (needs space for KYBER_POLYBYTES bytes)
*              - const poly *a:    pointer to input polynomial
**************************************************/
void PQCLEAN_KYBER768_CLEAN_poly_tobytes(uint8_t *r, poly *a) {
    int16_t t0, t1;

    PQCLEAN_KYBER768_CLEAN_poly_csubq(a);

    for (size_t i = 0; i < KYBER_N / 2; i++) {
        t0 = a->coeffs[2 * i];
        t1 = a->coeffs[2 * i + 1];
        r[3 * i]     = t0 & 0xff;
        r[3 * i + 1] = (uint8_t)((t0 >> 8) | ((t1 & 0xf) << 4));
        r[3 * i + 2] = (uint8_t)(t1 >> 4);
    }
}

/*************************************************
* Name:        poly_frombytes
*
* Description: De-serialization of a polynomial;
*              inverse of poly_tobytes
*
* Arguments:   - poly *r:                pointer to output polynomial
*              - const uint8_t *a: pointer to input byte array (of KYBER_POLYBYTES bytes)
**************************************************/
void PQCLEAN_KYBER768_CLEAN_poly_frombytes(poly *r, const uint8_t *a) {
    for (size_t i = 0; i < KYBER_N / 2; i++) {
        r->coeffs[2 * i]     = (int16_t)(a[3 * i]          | ((uint16_t)a[3 * i + 1] & 0x0f) << 8);
        r->coeffs[2 * i + 1] = (int16_t)(a[3 * i + 1] >> 4 | ((uint16_t)a[3 * i + 2] & 0xff) << 4);
    }
}

/*************************************************
* Name:        poly_getnoise
*
* Description: Sample a polynomial deterministically from a seed and a nonce,
*              with output polynomial close to centered binomial distribution
*              with parameter KYBER_ETA
*
* Arguments:   - poly *r:                   pointer to output polynomial
*              - const uint8_t *seed: pointer to input seed (pointing to array of length KYBER_SYMBYTES bytes)
*              - uint8_t nonce:       one-byte input nonce
**************************************************/
void PQCLEAN_KYBER768_CLEAN_poly_getnoise(poly *r, const uint8_t *seed, uint8_t nonce) {
    uint8_t buf[KYBER_ETA * KYBER_N / 4];

    prf(buf, KYBER_ETA * KYBER_N / 4, seed, nonce);
    PQCLEAN_KYBER768_CLEAN_cbd(r, buf);
}

/*************************************************
* Name:        poly_ntt
*
* Description: Computes negacyclic number-theoretic transform (NTT) of
*              a polynomial in place;
*              inputs assumed to be in normal order, output in bitreversed order
*
* Arguments:   - uint16_t *r: pointer to in/output polynomial
**************************************************/
void PQCLEAN_KYBER768_CLEAN_poly_ntt(poly *r) {
    PQCLEAN_KYBER768_CLEAN_ntt(r->coeffs);
    PQCLEAN_KYBER768_CLEAN_poly_reduce(r);
}

/*************************************************
* Name:        poly_invntt
*
* Description: Computes inverse of negacyclic number-theoretic transform (NTT) of
*              a polynomial in place;
*              inputs assumed to be in bitreversed order, output in normal order
*
* Arguments:   - uint16_t *a: pointer to in/output polynomial
**************************************************/
void PQCLEAN_KYBER768_CLEAN_poly_invntt(poly *r) {
    PQCLEAN_KYBER768_CLEAN_invntt(r->coeffs);
}

/*************************************************
* Name:        poly_basemul
*
* Description: Multiplication of two polynomials in NTT domain
*
* Arguments:   - poly *r:       pointer to output polynomial
*              - const poly *a: pointer to first input polynomial
*              - const poly *b: pointer to second input polynomial
**************************************************/
void PQCLEAN_KYBER768_CLEAN_poly_basemul(poly *r, const poly *a, const poly *b) {
    for (size_t i = 0; i < KYBER_N / 4; ++i) {
        PQCLEAN_KYBER768_CLEAN_basemul(
            r->coeffs + 4 * i,
            a->coeffs + 4 * i,
            b->coeffs + 4 * i,
            PQCLEAN_KYBER768_CLEAN_zetas[64 + i]);
        PQCLEAN_KYBER768_CLEAN_basemul(
            r->coeffs + 4 * i + 2,
            a->coeffs + 4 * i + 2,
            b->coeffs + 4 * i + 2,
            -PQCLEAN_KYBER768_CLEAN_zetas[64 + i]);
    }
}

/*************************************************
* Name:        poly_frommont
*
* Description: Inplace conversion of all coefficients of a polynomial
*              from Montgomery domain to normal domain
*
* Arguments:   - poly *r:       pointer to input/output polynomial
**************************************************/
void PQCLEAN_KYBER768_CLEAN_poly_frommont(poly *r) {
    const int16_t f = (1ULL << 32) % KYBER_Q;

    for (size_t i = 0; i < KYBER_N; i++) {
        r->coeffs[i] = PQCLEAN_KYBER768_CLEAN_montgomery_reduce(
                           (int32_t)r->coeffs[i] * f);
    }
}

/*************************************************
* Name:        poly_reduce
*
* Description: Applies Barrett reduction to all coefficients of a polynomial
*              for details of the Barrett reduction see comments in reduce.c
*
* Arguments:   - poly *r:       pointer to input/output polynomial
**************************************************/
void PQCLEAN_KYBER768_CLEAN_poly_reduce(poly *r) {
    for (size_t i = 0; i < KYBER_N; i++) {
        r->coeffs[i] = PQCLEAN_KYBER768_CLEAN_barrett_reduce(r->coeffs[i]);
    }
}

/*************************************************
* Name:        poly_csubq
*
* Description: Applies conditional subtraction of q to each coefficient of a polynomial
*              for details of conditional subtraction of q see comments in reduce.c
*
* Arguments:   - poly *r:       pointer to input/output polynomial
**************************************************/
void PQCLEAN_KYBER768_CLEAN_poly_csubq(poly *r) {
    for (size_t i = 0; i < KYBER_N; i++) {
        r->coeffs[i] = PQCLEAN_KYBER768_CLEAN_csubq(r->coeffs[i]);
    }
}

/*************************************************
* Name:        poly_add
*
* Description: Add two polynomials
*
* Arguments: - poly *r:       pointer to output polynomial
*            - const poly *a: pointer to first input polynomial
*            - const poly *b: pointer to second input polynomial
**************************************************/
void PQCLEAN_KYBER768_CLEAN_poly_add(poly *r, const poly *a, const poly *b) {
    for (size_t i = 0; i < KYBER_N; i++) {
        r->coeffs[i] = a->coeffs[i] + b->coeffs[i];
    }
}

/*************************************************
* Name:        poly_sub
*
* Description: Subtract two polynomials
*
* Arguments: - poly *r:       pointer to output polynomial
*            - const poly *a: pointer to first input polynomial
*            - const poly *b: pointer to second input polynomial
**************************************************/
void PQCLEAN_KYBER768_CLEAN_poly_sub(poly *r, const poly *a, const poly *b) {
    for (size_t i = 0; i < KYBER_N; i++) {
        r->coeffs[i] = a->coeffs[i] - b->coeffs[i];
    }
}

/*************************************************
* Name:        poly_frommsg
*
* Description: Convert 32-byte message to polynomial
*
* Arguments:   - poly *r:                  pointer to output polynomial
*              - const uint8_t *msg: pointer to input message
**************************************************/
void PQCLEAN_KYBER768_CLEAN_poly_frommsg(poly *r, const uint8_t msg[KYBER_SYMBYTES]) {
    uint16_t mask;

    for (size_t i = 0; i < KYBER_SYMBYTES; i++) {
        for (size_t j = 0; j < 8; j++) {
            mask = -((msg[i] >> j) & 1);
            r->coeffs[8 * i + j] = mask & ((KYBER_Q + 1) / 2);
        }
    }
}

/*************************************************
* Name:        poly_tomsg
*
* Description: Convert polynomial to 32-byte message
*
* Arguments:   - uint8_t *msg: pointer to output message
*              - const poly *a:      pointer to input polynomial
**************************************************/
void PQCLEAN_KYBER768_CLEAN_poly_tomsg(uint8_t msg[KYBER_SYMBYTES], poly *a) {
    uint16_t t;

    PQCLEAN_KYBER768_CLEAN_poly_csubq(a);

    for (size_t i = 0; i < KYBER_SYMBYTES; i++) {
        msg[i] = 0;
        for (size_t j = 0; j < 8; j++) {
            t = (((a->coeffs[8 * i + j] << 1) + KYBER_Q / 2) / KYBER_Q) & 1;
            msg[i] |= t << j;
        }
    }
}