pqc/crypto_kem/kyber768/avx2/indcpa.c

#include "cbd.h"
#include "indcpa.h"
#include "ntt.h"
#include "poly.h"
#include "polyvec.h"
#include "randombytes.h"
#include "rejsample.h"
#include "symmetric.h"

/*************************************************
* Name:        pack_pk
*
* Description: Serialize the public key as concatenation of the
*              compressed and serialized vector of polynomials pk
*              and the public seed used to generate the matrix A.
*
* Arguments:   uint8_t *r:          pointer to the output serialized public key
*              const poly *pk:            pointer to the input public-key polynomial
*              const uint8_t *seed: pointer to the input public seed
**************************************************/
static void pack_pk(uint8_t *r, polyvec *pk, const uint8_t *seed) {
    PQCLEAN_KYBER768_AVX2_polyvec_tobytes(r, pk);
    for (size_t i = 0; i < KYBER_SYMBYTES; i++) {
        r[i + KYBER_POLYVECBYTES] = seed[i];
    }
}

/*************************************************
* Name:        unpack_pk
*
* Description: De-serialize and decompress public key from a byte array;
*              approximate inverse of pack_pk
*
* Arguments:   - polyvec *pk:                   pointer to output public-key vector of polynomials
*              - uint8_t *seed:           pointer to output seed to generate matrix A
*              - const uint8_t *packedpk: pointer to input serialized public key
**************************************************/
static void unpack_pk(polyvec *pk, uint8_t *seed, const uint8_t *packedpk) {
    PQCLEAN_KYBER768_AVX2_polyvec_frombytes(pk, packedpk);
    for (size_t i = 0; i < KYBER_SYMBYTES; i++) {
        seed[i] = packedpk[i + KYBER_POLYVECBYTES];
    }
}

/*************************************************
* Name:        pack_sk
*
* Description: Serialize the secret key
*
* Arguments:   - uint8_t *r:  pointer to output serialized secret key
*              - const polyvec *sk: pointer to input vector of polynomials (secret key)
**************************************************/
static void pack_sk(uint8_t *r, polyvec *sk) {
    PQCLEAN_KYBER768_AVX2_polyvec_tobytes(r, sk);
}

/*************************************************
* Name:        unpack_sk
*
* Description: De-serialize the secret key;
*              inverse of pack_sk
*
* Arguments:   - polyvec *sk:                   pointer to output vector of polynomials (secret key)
*              - const uint8_t *packedsk: pointer to input serialized secret key
**************************************************/
static void unpack_sk(polyvec *sk, const uint8_t *packedsk) {
    PQCLEAN_KYBER768_AVX2_polyvec_frombytes(sk, packedsk);
}

/*************************************************
* Name:        pack_ciphertext
*
* Description: Serialize the ciphertext as concatenation of the
*              compressed and serialized vector of polynomials b
*              and the compressed and serialized polynomial v
*
* Arguments:   uint8_t *r:          pointer to the output serialized ciphertext
*              const poly *pk:            pointer to the input vector of polynomials b
*              const uint8_t *seed: pointer to the input polynomial v
**************************************************/
static void pack_ciphertext(uint8_t *r, polyvec *b, poly *v) {
    PQCLEAN_KYBER768_AVX2_polyvec_compress(r, b);
    PQCLEAN_KYBER768_AVX2_poly_compress(r + KYBER_POLYVECCOMPRESSEDBYTES, v);
}

/*************************************************
* Name:        unpack_ciphertext
*
* Description: De-serialize and decompress ciphertext from a byte array;
*              approximate inverse of pack_ciphertext
*
* Arguments:   - polyvec *b:             pointer to the output vector of polynomials b
*              - poly *v:                pointer to the output polynomial v
*              - const uint8_t *c: pointer to the input serialized ciphertext
**************************************************/
static void unpack_ciphertext(polyvec *b, poly *v, const uint8_t *c) {
    PQCLEAN_KYBER768_AVX2_polyvec_decompress(b, c);
    PQCLEAN_KYBER768_AVX2_poly_decompress(v, c + KYBER_POLYVECCOMPRESSEDBYTES);
}

static size_t rej_uniform_ref(int16_t *r, size_t len, const uint8_t *buf, size_t buflen) {
    unsigned int ctr, pos;
    uint16_t val;

    ctr = pos = 0;
    while (ctr < len && pos + 2 <= buflen) {
        val = (uint16_t)(buf[pos] | ((uint16_t)buf[pos + 1] << 8));
        pos += 2;

        if (val < 19 * KYBER_Q) {
            val -= ((uint32_t)val * 20159 >> 26) * KYBER_Q; // Barrett reduction
            r[ctr++] = (int16_t)val;
        }
    }

    return ctr;
}

#define gen_a(A,B)  gen_matrix(A,B,0)
#define gen_at(A,B) gen_matrix(A,B,1)

/*************************************************
* Name:        gen_matrix
*
* Description: Deterministically generate matrix A (or the transpose of A)
*              from a seed. Entries of the matrix are polynomials that look
*              uniformly random. Performs rejection sampling on output of
*              a XOF
*
* Arguments:   - polyvec *a:                pointer to ouptput matrix A
*              - const uint8_t *seed: pointer to input seed
*              - int transposed:            boolean deciding whether A or A^T is generated
**************************************************/
#define  GEN_MATRIX_MAXNBLOCKS ((530+XOF_BLOCKBYTES)/XOF_BLOCKBYTES)    /* 530 is expected number of required bytes */
static void gen_matrix(polyvec *a, const uint8_t *seed, int transposed) {
    size_t ctr0, ctr1, ctr2, ctr3, bufbytes;
    union {
        uint8_t x[4][XOF_BLOCKBYTES * GEN_MATRIX_MAXNBLOCKS];
        __m256i _dummy;
    } buf;
    keccak4x_state state;
    keccak_state state1x;

    if (transposed) {
        PQCLEAN_KYBER768_AVX2_kyber_shake128x4_absorb(&state, seed, 0, 256, 512, 1);
    } else {
        PQCLEAN_KYBER768_AVX2_kyber_shake128x4_absorb(&state, seed, 0, 1, 2, 256);
    }

    PQCLEAN_KYBER768_AVX2_shake128x4_squeezeblocks(buf.x[0], buf.x[1], buf.x[2], buf.x[3], GEN_MATRIX_MAXNBLOCKS, &state);
    bufbytes = GEN_MATRIX_MAXNBLOCKS * XOF_BLOCKBYTES;

    ctr0 = PQCLEAN_KYBER768_AVX2_rej_uniform(a[0].vec[0].coeffs, KYBER_N, buf.x[0], bufbytes);
    ctr1 = PQCLEAN_KYBER768_AVX2_rej_uniform(a[0].vec[1].coeffs, KYBER_N, buf.x[1], bufbytes);
    ctr2 = PQCLEAN_KYBER768_AVX2_rej_uniform(a[0].vec[2].coeffs, KYBER_N, buf.x[2], bufbytes);
    ctr3 = PQCLEAN_KYBER768_AVX2_rej_uniform(a[1].vec[0].coeffs, KYBER_N, buf.x[3], bufbytes);

    while (ctr0 < KYBER_N || ctr1 < KYBER_N || ctr2 < KYBER_N || ctr3 < KYBER_N) {
        PQCLEAN_KYBER768_AVX2_shake128x4_squeezeblocks(buf.x[0], buf.x[1], buf.x[2], buf.x[3], 1, &state);
        bufbytes = XOF_BLOCKBYTES;

        ctr0 += rej_uniform_ref(a[0].vec[0].coeffs + ctr0, KYBER_N - ctr0, buf.x[0], bufbytes);
        ctr1 += rej_uniform_ref(a[0].vec[1].coeffs + ctr1, KYBER_N - ctr1, buf.x[1], bufbytes);
        ctr2 += rej_uniform_ref(a[0].vec[2].coeffs + ctr2, KYBER_N - ctr2, buf.x[2], bufbytes);
        ctr3 += rej_uniform_ref(a[1].vec[0].coeffs + ctr3, KYBER_N - ctr3, buf.x[3], bufbytes);
    }

    PQCLEAN_KYBER768_AVX2_poly_nttunpack(&a[0].vec[0]);
    PQCLEAN_KYBER768_AVX2_poly_nttunpack(&a[0].vec[1]);
    PQCLEAN_KYBER768_AVX2_poly_nttunpack(&a[0].vec[2]);
    PQCLEAN_KYBER768_AVX2_poly_nttunpack(&a[1].vec[0]);

    if (transposed) {
        PQCLEAN_KYBER768_AVX2_kyber_shake128x4_absorb(&state, seed, 257, 513, 2, 258);
    } else {
        PQCLEAN_KYBER768_AVX2_kyber_shake128x4_absorb(&state, seed, 257, 258, 512, 513);
    }

    PQCLEAN_KYBER768_AVX2_shake128x4_squeezeblocks(buf.x[0], buf.x[1], buf.x[2], buf.x[3], GEN_MATRIX_MAXNBLOCKS, &state);
    bufbytes = GEN_MATRIX_MAXNBLOCKS * XOF_BLOCKBYTES;

    ctr0 = PQCLEAN_KYBER768_AVX2_rej_uniform(a[1].vec[1].coeffs, KYBER_N, buf.x[0], bufbytes);
    ctr1 = PQCLEAN_KYBER768_AVX2_rej_uniform(a[1].vec[2].coeffs, KYBER_N, buf.x[1], bufbytes);
    ctr2 = PQCLEAN_KYBER768_AVX2_rej_uniform(a[2].vec[0].coeffs, KYBER_N, buf.x[2], bufbytes);
    ctr3 = PQCLEAN_KYBER768_AVX2_rej_uniform(a[2].vec[1].coeffs, KYBER_N, buf.x[3], bufbytes);

    while (ctr0 < KYBER_N || ctr1 < KYBER_N || ctr2 < KYBER_N || ctr3 < KYBER_N) {
        PQCLEAN_KYBER768_AVX2_shake128x4_squeezeblocks(buf.x[0], buf.x[1], buf.x[2], buf.x[3], 1, &state);
        bufbytes = XOF_BLOCKBYTES;

        ctr0 += rej_uniform_ref(a[1].vec[1].coeffs + ctr0, KYBER_N - ctr0, buf.x[0], bufbytes);
        ctr1 += rej_uniform_ref(a[1].vec[2].coeffs + ctr1, KYBER_N - ctr1, buf.x[1], bufbytes);
        ctr2 += rej_uniform_ref(a[2].vec[0].coeffs + ctr2, KYBER_N - ctr2, buf.x[2], bufbytes);
        ctr3 += rej_uniform_ref(a[2].vec[1].coeffs + ctr3, KYBER_N - ctr3, buf.x[3], bufbytes);
    }

    PQCLEAN_KYBER768_AVX2_poly_nttunpack(&a[1].vec[1]);
    PQCLEAN_KYBER768_AVX2_poly_nttunpack(&a[1].vec[2]);
    PQCLEAN_KYBER768_AVX2_poly_nttunpack(&a[2].vec[0]);
    PQCLEAN_KYBER768_AVX2_poly_nttunpack(&a[2].vec[1]);

    PQCLEAN_KYBER768_AVX2_kyber_shake128_absorb(&state1x, seed, 2, 2);

    PQCLEAN_KYBER768_AVX2_kyber_shake128_squeezeblocks(buf.x[0], GEN_MATRIX_MAXNBLOCKS, &state1x);
    bufbytes = GEN_MATRIX_MAXNBLOCKS * XOF_BLOCKBYTES;

    ctr0 = PQCLEAN_KYBER768_AVX2_rej_uniform(a[2].vec[2].coeffs, KYBER_N, buf.x[0], bufbytes);

    while (ctr0 < KYBER_N) {
        PQCLEAN_KYBER768_AVX2_kyber_shake128_squeezeblocks(buf.x[0], 1, &state1x);
        bufbytes = XOF_BLOCKBYTES;

        ctr0 += rej_uniform_ref(a[2].vec[2].coeffs + ctr0, KYBER_N - ctr0, buf.x[0], bufbytes);
    }

    xof_ctx_release(&state1x);

    PQCLEAN_KYBER768_AVX2_poly_nttunpack(&a[2].vec[2]);
}

/*************************************************
* Name:        indcpa_keypair
*
* Description: Generates public and private key for the CPA-secure
*              public-key encryption scheme underlying Kyber
*
* Arguments:   - uint8_t *pk: pointer to output public key (of length KYBER_INDCPA_PUBLICKEYBYTES bytes)
*              - uint8_t *sk: pointer to output private key (of length KYBER_INDCPA_SECRETKEYBYTES bytes)
**************************************************/
void PQCLEAN_KYBER768_AVX2_indcpa_keypair(uint8_t *pk, uint8_t *sk) {
    polyvec a[KYBER_K], skpv, e, pkpv;
    uint8_t buf[2 * KYBER_SYMBYTES];
    const uint8_t *publicseed = buf;
    const uint8_t *noiseseed = buf + KYBER_SYMBYTES;
    uint8_t nonce = 0;

    randombytes(buf, KYBER_SYMBYTES);
    hash_g(buf, buf, KYBER_SYMBYTES);

    gen_a(a, publicseed);

    PQCLEAN_KYBER768_AVX2_poly_getnoise4x(skpv.vec + 0, skpv.vec + 1, skpv.vec + 2, e.vec + 0, noiseseed, nonce + 0, nonce + 1, nonce + 2, nonce + 3);
    PQCLEAN_KYBER768_AVX2_poly_getnoise4x(e.vec + 1, e.vec + 2, pkpv.vec + 0, pkpv.vec + 1, noiseseed, nonce + 4, nonce + 5, 0, 0);

    PQCLEAN_KYBER768_AVX2_polyvec_ntt(&skpv);
    PQCLEAN_KYBER768_AVX2_polyvec_ntt(&e);

    // matrix-vector multiplication
    for (size_t i = 0; i < KYBER_K; i++) {
        PQCLEAN_KYBER768_AVX2_polyvec_pointwise_acc(pkpv.vec + i, a + i, &skpv);
        PQCLEAN_KYBER768_AVX2_poly_frommont(pkpv.vec + i);
    }

    PQCLEAN_KYBER768_AVX2_polyvec_add(&pkpv, &pkpv, &e);
    PQCLEAN_KYBER768_AVX2_polyvec_reduce(&pkpv);

    pack_sk(sk, &skpv);
    pack_pk(pk, &pkpv, publicseed);
}

/*************************************************
* Name:        indcpa_enc
*
* Description: Encryption function of the CPA-secure
*              public-key encryption scheme underlying Kyber.
*
* Arguments:   - uint8_t *c:          pointer to output ciphertext (of length KYBER_INDCPA_BYTES bytes)
*              - const uint8_t *m:    pointer to input message (of length KYBER_INDCPA_MSGBYTES bytes)
*              - const uint8_t *pk:   pointer to input public key (of length KYBER_INDCPA_PUBLICKEYBYTES bytes)
*              - const uint8_t *coin: pointer to input random coins used as seed (of length KYBER_SYMBYTES bytes)
*                                           to deterministically generate all randomness
**************************************************/
void PQCLEAN_KYBER768_AVX2_indcpa_enc(uint8_t *c,
                                      const uint8_t *m,
                                      const uint8_t *pk,
                                      const uint8_t *coins) {
    polyvec at[KYBER_K], pkpv, sp, ep, bp;
    poly k, v, epp;
    uint8_t seed[KYBER_SYMBYTES];
    uint8_t nonce = 0;

    unpack_pk(&pkpv, seed, pk);
    PQCLEAN_KYBER768_AVX2_poly_frommsg(&k, m);
    gen_at(at, seed);

    PQCLEAN_KYBER768_AVX2_poly_getnoise4x(sp.vec + 0, sp.vec + 1, sp.vec + 2, ep.vec + 0, coins, nonce + 0, nonce + 1, nonce + 2, nonce + 3);
    PQCLEAN_KYBER768_AVX2_poly_getnoise4x(ep.vec + 1, ep.vec + 2, &epp, bp.vec + 0, coins, nonce + 4, nonce + 5, nonce + 6, 0);

    PQCLEAN_KYBER768_AVX2_polyvec_ntt(&sp);

    // matrix-vector multiplication
    for (size_t i = 0; i < KYBER_K; i++) {
        PQCLEAN_KYBER768_AVX2_polyvec_pointwise_acc(bp.vec + i, at + i, &sp);
    }

    PQCLEAN_KYBER768_AVX2_polyvec_pointwise_acc(&v, &pkpv, &sp);

    PQCLEAN_KYBER768_AVX2_polyvec_invntt(&bp);
    PQCLEAN_KYBER768_AVX2_poly_invntt(&v);

    PQCLEAN_KYBER768_AVX2_polyvec_add(&bp, &bp, &ep);
    PQCLEAN_KYBER768_AVX2_poly_add(&v, &v, &epp);
    PQCLEAN_KYBER768_AVX2_poly_add(&v, &v, &k);
    PQCLEAN_KYBER768_AVX2_polyvec_reduce(&bp);
    PQCLEAN_KYBER768_AVX2_poly_reduce(&v);

    pack_ciphertext(c, &bp, &v);
}

/*************************************************
* Name:        indcpa_dec
*
* Description: Decryption function of the CPA-secure
*              public-key encryption scheme underlying Kyber.
*
* Arguments:   - uint8_t *m:        pointer to output decrypted message (of length KYBER_INDCPA_MSGBYTES)
*              - const uint8_t *c:  pointer to input ciphertext (of length KYBER_INDCPA_BYTES)
*              - const uint8_t *sk: pointer to input secret key (of length KYBER_INDCPA_SECRETKEYBYTES)
**************************************************/
void PQCLEAN_KYBER768_AVX2_indcpa_dec(uint8_t *m,
                                      const uint8_t *c,
                                      const uint8_t *sk) {
    polyvec bp, skpv;
    poly v, mp;

    unpack_ciphertext(&bp, &v, c);
    unpack_sk(&skpv, sk);

    PQCLEAN_KYBER768_AVX2_polyvec_ntt(&bp);
    PQCLEAN_KYBER768_AVX2_polyvec_pointwise_acc(&mp, &skpv, &bp);
    PQCLEAN_KYBER768_AVX2_poly_invntt(&mp);

    PQCLEAN_KYBER768_AVX2_poly_sub(&mp, &v, &mp);
    PQCLEAN_KYBER768_AVX2_poly_reduce(&mp);

    PQCLEAN_KYBER768_AVX2_poly_tomsg(m, &mp);
}