Function check_randomness

FHEOffline/DistKeyGen.cpp:207–280

* Simulate an execution of KeyGen to check that these nplayers seeds * produce the correct public key. */

 * produce the correct public key.
 */
void check_randomness(vector<octetStream>& seeds,
                      const Ciphertext& actual_sw,const FHE_PK& pk,
                      const Ciphertext& enc_dash,
                      int num_players)
{
    const FHE_Params& params=actual_sw.get_params();

    vector<DistKeyGen> playerKeys(num_players, {params, pk.p()});
    DistKeyGen globalKey(params, pk.p());

    Rq_Element b(Rq_Element(params.FFTD(), evaluation, evaluation));
    Rq_Element zero(Rq_Element(params.FFTD(), polynomial,polynomial));
    zero.assign_zero();

    Ciphertext ed(params), ed_sum(params), ezero(params), ezero_sum(params);
    PRNG G;

    // Re-create the randomness from these seeds
    for (int i = 0; i < num_players; i++)
      { G.SetSeed(seeds[i].get_data());
#ifdef VERBOSE_KEYGEN
        cout << "\tSeed for player " << i << " is..." << seeds[i] << endl;
#endif
        playerKeys[i].Gen_Random_Data(G);
        globalKey += playerKeys[i];
      }
    mul(b, globalKey.a, globalKey.secret);
    mul(globalKey.e, globalKey.e, pk.p());
    add(b, b, globalKey.e);

    // Check the main pk (a,b)
    if (!pk.a().equals(globalKey.a))
        throw bad_keygen("a doesn't match");
    if (!pk.b().equals(b))
        throw bad_keygen("b doesn't match");


    // Compute the key-switching data
    for (int i = 0; i < num_players; i++)
    {
        Rq_Element zero_q(params.FFTD(), evaluation, evaluation);
        zero_q.assign_zero();
        Encrypt_Rq_Element(ed, zero_q, playerKeys[i].rc1, pk);
        add(ed_sum, ed_sum, ed);
        pk.quasi_encrypt(ezero, zero, playerKeys[i].rc2);
        add(ezero_sum, ezero_sum, ezero);
    }

    globalKey.secret.raise_level();
    Rq_Element ps(globalKey.secret);
    ps.mul_by_p1(); ps.negate();

    Rq_Element enc0(ed_sum.c0());
    Rq_Element enc1(ed_sum.c1());

    add(enc0, enc0, ps);

    if (enc1 != enc_dash.c1())