pqcrypto/crypto_kem/kyber768/clean/indcpa.c

#include "indcpa.h"
#include "fips202.h"
#include "ntt.h"
#include "poly.h"
#include "polyvec.h"
#include "randombytes.h"
#include <string.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:   unsigned char *r:          pointer to the output serialized
 *public key const poly *pk:            pointer to the input public-key
 *polynomial const unsigned char *seed: pointer to the input public seed
 **************************************************/
static void pack_pk(unsigned char *r, const polyvec *pk,
                    const unsigned char *seed) {
  int i;
  polyvec_compress(r, pk);
  for (i = 0; i < KYBER_SYMBYTES; i++) {
    r[i + KYBER_POLYVECCOMPRESSEDBYTES] = 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
 *              - unsigned char *seed:           pointer to output seed to
 *generate matrix A
 *              - const unsigned char *packedpk: pointer to input serialized
 *public key
 **************************************************/
static void unpack_pk(polyvec *pk, unsigned char *seed,
                      const unsigned char *packedpk) {
  int i;
  polyvec_decompress(pk, packedpk);

  for (i = 0; i < KYBER_SYMBYTES; i++) {
    seed[i] = packedpk[i + KYBER_POLYVECCOMPRESSEDBYTES];
  }
}

/*************************************************
 * 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:   unsigned char *r:          pointer to the output serialized
 *ciphertext const poly *pk:            pointer to the input vector of
 *polynomials b const unsigned char *seed: pointer to the input polynomial v
 **************************************************/
static void pack_ciphertext(unsigned char *r, const polyvec *b, const poly *v) {
  polyvec_compress(r, b);
  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 unsigned char *c: pointer to the input serialized
 *ciphertext
 **************************************************/
static void unpack_ciphertext(polyvec *b, poly *v, const unsigned char *c) {
  polyvec_decompress(b, c);
  poly_decompress(v, c + KYBER_POLYVECCOMPRESSEDBYTES);
}

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

#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
 *              SHAKE-128
 *
 * Arguments:   - polyvec *a:                pointer to ouptput matrix A
 *              - const unsigned char *seed: pointer to input seed
 *              - int transposed:            boolean deciding whether A or A^T
 *is generated
 **************************************************/
void gen_matrix(polyvec *a, const unsigned char *seed,
                int transposed) // Not static for benchmarking
{
  unsigned int pos = 0, ctr;
  uint16_t val;
  unsigned int nblocks;
  const unsigned int maxnblocks = 4;
  uint8_t buf[SHAKE128_RATE * maxnblocks];
  int i, j;
  uint64_t state[25]; // SHAKE state
  unsigned char extseed[KYBER_SYMBYTES + 2];

  for (i = 0; i < KYBER_SYMBYTES; i++) {
    extseed[i] = seed[i];
  }

  for (i = 0; i < KYBER_K; i++) {
    for (j = 0; j < KYBER_K; j++) {
      ctr = pos = 0;
      nblocks = maxnblocks;
      if (transposed) {
        extseed[KYBER_SYMBYTES] = i;
        extseed[KYBER_SYMBYTES + 1] = j;
      } else {
        extseed[KYBER_SYMBYTES] = j;
        extseed[KYBER_SYMBYTES + 1] = i;
      }

      shake128_absorb(state, extseed, KYBER_SYMBYTES + 2);
      shake128_squeezeblocks(buf, nblocks, state);

      while (ctr < KYBER_N) {
        val = (buf[pos] | ((uint16_t)buf[pos + 1] << 8)) & 0x1fff;
        if (val < KYBER_Q) {
          a[i].vec[j].coeffs[ctr++] = val;
        }
        pos += 2;

        if (pos > SHAKE128_RATE * nblocks - 2) {
          nblocks = 1;
          shake128_squeezeblocks(buf, nblocks, state);
          pos = 0;
        }
      }
    }
  }
}

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

  randombytes(buf, KYBER_SYMBYTES);
  sha3_512(buf, buf, KYBER_SYMBYTES);

  gen_a(a, publicseed);

  for (i = 0; i < KYBER_K; i++) {
    poly_getnoise(skpv.vec + i, noiseseed, nonce++);
  }

  polyvec_ntt(&skpv);

  for (i = 0; i < KYBER_K; i++) {
    poly_getnoise(e.vec + i, noiseseed, nonce++);
  }

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

  polyvec_invntt(&pkpv);
  polyvec_add(&pkpv, &pkpv, &e);

  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:   - unsigned char *c:          pointer to output ciphertext (of
 *length KYBER_INDCPA_BYTES bytes)
 *              - const unsigned char *m:    pointer to input message (of length
 *KYBER_INDCPA_MSGBYTES bytes)
 *              - const unsigned char *pk:   pointer to input public key (of
 *length KYBER_INDCPA_PUBLICKEYBYTES bytes)
 *              - const unsigned char *coin: pointer to input random coins used
 *as seed (of length KYBER_SYMBYTES bytes) to deterministically generate all
 *randomness
 **************************************************/
void indcpa_enc(unsigned char *c, const unsigned char *m,
                const unsigned char *pk, const unsigned char *coins) {
  polyvec sp, pkpv, ep, at[KYBER_K], bp;
  poly v, k, epp;
  unsigned char seed[KYBER_SYMBYTES];
  int i;
  unsigned char nonce = 0;

  unpack_pk(&pkpv, seed, pk);

  poly_frommsg(&k, m);

  polyvec_ntt(&pkpv);

  gen_at(at, seed);

  for (i = 0; i < KYBER_K; i++) {
    poly_getnoise(sp.vec + i, coins, nonce++);
  }

  polyvec_ntt(&sp);

  for (i = 0; i < KYBER_K; i++) {
    poly_getnoise(ep.vec + i, coins, nonce++);
  }

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

  polyvec_invntt(&bp);
  polyvec_add(&bp, &bp, &ep);

  polyvec_pointwise_acc(&v, &pkpv, &sp);
  poly_invntt(&v);

  poly_getnoise(&epp, coins, nonce++);

  poly_add(&v, &v, &epp);
  poly_add(&v, &v, &k);

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

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

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

  polyvec_ntt(&bp);

  polyvec_pointwise_acc(&mp, &skpv, &bp);
  poly_invntt(&mp);

  poly_sub(&mp, &mp, &v);

  poly_tomsg(m, &mp);
}