poly.c

#include "cbd.h"
#include "ntt.h"
#include "params.h"
#include "poly.h"
#include "reduce.h"
#include "symmetric.h"
#include <stdint.h>

/*************************************************
* Name:        PQCLEAN_KYBER512_CLEAN_poly_compress
*
* Description: Compression and subsequent serialization of a polynomial
*
* Arguments:   - uint8_t *r: pointer to output byte array
*                            (of length KYBER_POLYCOMPRESSEDBYTES)
*              - const poly *a: pointer to input polynomial
**************************************************/
void PQCLEAN_KYBER512_CLEAN_poly_compress(uint8_t r[KYBER_POLYCOMPRESSEDBYTES], const poly *a) {
    unsigned int i, j;
    int32_t u;
    uint32_t d0;
    uint8_t t[8];

    for (i = 0; i < KYBER_N / 8; i++) {
        for (j = 0; j < 8; j++) {
            // map to positive standard representatives
            u  = a->coeffs[8 * i + j];
            u += (u >> 15) & KYBER_Q;
            /*    t[j] = ((((uint16_t)u << 4) + KYBER_Q/2)/KYBER_Q) & 15; */
            d0 = u << 4;
            d0 += 1665;
            d0 *= 80635;
            d0 >>= 28;
            t[j] = d0 & 0xf;
        }

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

/*************************************************
* Name:        PQCLEAN_KYBER512_CLEAN_poly_decompress
*
* Description: De-serialization and subsequent decompression of a polynomial;
*              approximate inverse of PQCLEAN_KYBER512_CLEAN_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_KYBER512_CLEAN_poly_decompress(poly *r, const uint8_t a[KYBER_POLYCOMPRESSEDBYTES]) {
    size_t i;

    for (i = 0; i < KYBER_N / 2; i++) {
        r->coeffs[2 * i + 0] = (((uint16_t)(a[0] & 15) * KYBER_Q) + 8) >> 4;
        r->coeffs[2 * i + 1] = (((uint16_t)(a[0] >> 4) * KYBER_Q) + 8) >> 4;
        a += 1;
    }
}

/*************************************************
* Name:        PQCLEAN_KYBER512_CLEAN_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_KYBER512_CLEAN_poly_tobytes(uint8_t r[KYBER_POLYBYTES], const poly *a) {
    size_t i;
    uint16_t t0, t1;

    for (i = 0; i < KYBER_N / 2; i++) {
        // map to positive standard representatives
        t0  = a->coeffs[2 * i];
        t0 += ((int16_t)t0 >> 15) & KYBER_Q;
        t1 = a->coeffs[2 * i + 1];
        t1 += ((int16_t)t1 >> 15) & KYBER_Q;
        r[3 * i + 0] = (uint8_t)(t0 >> 0);
        r[3 * i + 1] = (uint8_t)((t0 >> 8) | (t1 << 4));
        r[3 * i + 2] = (uint8_t)(t1 >> 4);
    }
}

/*************************************************
* Name:        PQCLEAN_KYBER512_CLEAN_poly_frombytes
*
* Description: De-serialization of a polynomial;
*              inverse of PQCLEAN_KYBER512_CLEAN_poly_tobytes
*
* Arguments:   - poly *r: pointer to output polynomial
*              - const uint8_t *a: pointer to input byte array
*                                  (of KYBER_POLYBYTES bytes)
**************************************************/
void PQCLEAN_KYBER512_CLEAN_poly_frombytes(poly *r, const uint8_t a[KYBER_POLYBYTES]) {
    size_t i;
    for (i = 0; i < KYBER_N / 2; i++) {
        r->coeffs[2 * i]   = ((a[3 * i + 0] >> 0) | ((uint16_t)a[3 * i + 1] << 8)) & 0xFFF;
        r->coeffs[2 * i + 1] = ((a[3 * i + 1] >> 4) | ((uint16_t)a[3 * i + 2] << 4)) & 0xFFF;
    }
}

/*************************************************
* Name:        PQCLEAN_KYBER512_CLEAN_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_KYBER512_CLEAN_poly_frommsg(poly *r, const uint8_t msg[KYBER_INDCPA_MSGBYTES]) {
    size_t i, j;
    int16_t mask;

    for (i = 0; i < KYBER_N / 8; i++) {
        for (j = 0; j < 8; j++) {
            mask = -(int16_t)((msg[i] >> j) & 1);
            r->coeffs[8 * i + j] = mask & ((KYBER_Q + 1) / 2);
        }
    }
}

/*************************************************
* Name:        PQCLEAN_KYBER512_CLEAN_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_KYBER512_CLEAN_poly_tomsg(uint8_t msg[KYBER_INDCPA_MSGBYTES], const poly *a) {
    unsigned int i, j;
    uint32_t t;

    for (i = 0; i < KYBER_N / 8; i++) {
        msg[i] = 0;
        for (j = 0; j < 8; j++) {
            t  = a->coeffs[8 * i + j];
            // t += ((int16_t)t >> 15) & KYBER_Q;
            // t  = (((t << 1) + KYBER_Q/2)/KYBER_Q) & 1;
            t <<= 1;
            t += 1665;
            t *= 80635;
            t >>= 28;
            t &= 1;
            msg[i] |= t << j;
        }
    }
}

/*************************************************
* Name:        PQCLEAN_KYBER512_CLEAN_poly_getnoise_eta1
*
* Description: Sample a polynomial deterministically from a seed and a nonce,
*              with output polynomial close to centered binomial distribution
*              with parameter KYBER_ETA1
*
* Arguments:   - poly *r: pointer to output polynomial
*              - const uint8_t *seed: pointer to input seed
*                                     (of length KYBER_SYMBYTES bytes)
*              - uint8_t nonce: one-byte input nonce
**************************************************/
void PQCLEAN_KYBER512_CLEAN_poly_getnoise_eta1(poly *r, const uint8_t seed[KYBER_SYMBYTES], uint8_t nonce) {
    uint8_t buf[KYBER_ETA1 * KYBER_N / 4];
    prf(buf, sizeof(buf), seed, nonce);
    PQCLEAN_KYBER512_CLEAN_poly_cbd_eta1(r, buf);
}

/*************************************************
* Name:        PQCLEAN_KYBER512_CLEAN_poly_getnoise_eta2
*
* Description: Sample a polynomial deterministically from a seed and a nonce,
*              with output polynomial close to centered binomial distribution
*              with parameter KYBER_ETA2
*
* Arguments:   - poly *r: pointer to output polynomial
*              - const uint8_t *seed: pointer to input seed
*                                     (of length KYBER_SYMBYTES bytes)
*              - uint8_t nonce: one-byte input nonce
**************************************************/
void PQCLEAN_KYBER512_CLEAN_poly_getnoise_eta2(poly *r, const uint8_t seed[KYBER_SYMBYTES], uint8_t nonce) {
    uint8_t buf[KYBER_ETA2 * KYBER_N / 4];
    prf(buf, sizeof(buf), seed, nonce);
    PQCLEAN_KYBER512_CLEAN_poly_cbd_eta2(r, buf);
}

/*************************************************
* Name:        PQCLEAN_KYBER512_CLEAN_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_KYBER512_CLEAN_poly_ntt(poly *r) {
    PQCLEAN_KYBER512_CLEAN_ntt(r->coeffs);
    PQCLEAN_KYBER512_CLEAN_poly_reduce(r);
}

/*************************************************
* Name:        PQCLEAN_KYBER512_CLEAN_poly_invntt_tomont
*
* 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_KYBER512_CLEAN_poly_invntt_tomont(poly *r) {
    PQCLEAN_KYBER512_CLEAN_invntt(r->coeffs);
}

/*************************************************
* Name:        PQCLEAN_KYBER512_CLEAN_poly_basemul_montgomery
*
* 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_KYBER512_CLEAN_poly_basemul_montgomery(poly *r, const poly *a, const poly *b) {
    size_t i;
    for (i = 0; i < KYBER_N / 4; i++) {
        PQCLEAN_KYBER512_CLEAN_basemul(&r->coeffs[4 * i], &a->coeffs[4 * i], &b->coeffs[4 * i], PQCLEAN_KYBER512_CLEAN_zetas[64 + i]);
        PQCLEAN_KYBER512_CLEAN_basemul(&r->coeffs[4 * i + 2], &a->coeffs[4 * i + 2], &b->coeffs[4 * i + 2], -PQCLEAN_KYBER512_CLEAN_zetas[64 + i]);
    }
}

/*************************************************
* Name:        PQCLEAN_KYBER512_CLEAN_poly_tomont
*
* Description: Inplace conversion of all coefficients of a polynomial
*              from normal domain to Montgomery domain
*
* Arguments:   - poly *r: pointer to input/output polynomial
**************************************************/
void PQCLEAN_KYBER512_CLEAN_poly_tomont(poly *r) {
    size_t i;
    const int16_t f = (1ULL << 32) % KYBER_Q;
    for (i = 0; i < KYBER_N; i++) {
        r->coeffs[i] = PQCLEAN_KYBER512_CLEAN_montgomery_reduce((int32_t)r->coeffs[i] * f);
    }
}

/*************************************************
* Name:        PQCLEAN_KYBER512_CLEAN_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_KYBER512_CLEAN_poly_reduce(poly *r) {
    size_t i;
    for (i = 0; i < KYBER_N; i++) {
        r->coeffs[i] = PQCLEAN_KYBER512_CLEAN_barrett_reduce(r->coeffs[i]);
    }
}

/*************************************************
* Name:        PQCLEAN_KYBER512_CLEAN_poly_add
*
* Description: Add two polynomials; no modular reduction is performed
*
* 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_KYBER512_CLEAN_poly_add(poly *r, const poly *a, const poly *b) {
    size_t i;
    for (i = 0; i < KYBER_N; i++) {
        r->coeffs[i] = a->coeffs[i] + b->coeffs[i];
    }
}

/*************************************************
* Name:        PQCLEAN_KYBER512_CLEAN_poly_sub
*
* Description: Subtract two polynomials; no modular reduction is performed
*
* 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_KYBER512_CLEAN_poly_sub(poly *r, const poly *a, const poly *b) {
    size_t i;
    for (i = 0; i < KYBER_N; i++) {
        r->coeffs[i] = a->coeffs[i] - b->coeffs[i];
    }
}