MP-SPDZ/FHEOffline/PairwiseSetup.cpp

/*
 * PairwiseSetup.cpp
 *
 */

#include <FHEOffline/PairwiseSetup.h>
#include "FHE/NoiseBounds.h"
#include "FHE/NTL-Subs.h"
#include "Math/Setup.h"
#include "FHEOffline/Proof.h"
#include "FHEOffline/PairwiseMachine.h"
#include "Tools/Commit.h"
#include "Tools/Bundle.h"

template <class FD>
void PairwiseSetup<FD>::init(const Player& P, int sec, int plaintext_length,
    int& extra_slack)
{
    cout << "Finding parameters for security " << sec << " and field size ~2^"
            << plaintext_length << endl;
    PRNG G;
    G.ReSeed();
    dirname = PREP_DIR;

    octetStream o;
    if (P.my_num() == 0)
    {
        extra_slack =
            generate_semi_setup(plaintext_length, sec, params, FieldD, true);
        params.pack(o);
        FieldD.pack(o);
        o.store(extra_slack);
        P.send_all(o);
    }
    else
    {
        P.receive_player(0, o);
        params.unpack(o);
        FieldD.unpack(o);
        FieldD.init_field();
        o.get(extra_slack);
    }

    alpha = FieldD;
    alpha.randomize(G, Diagonal);
    alphai = alpha.element(0);
}

template <class FD>
void PairwiseSetup<FD>::secure_init(Player& P, PairwiseMachine& machine, int plaintext_length, int sec)
{
    machine.sec = sec;
    sec = max(sec, 40);
    machine.drown_sec = sec;
    string filename = PREP_DIR "Params-" + FD::T::type_string() + "-"
            + to_string(plaintext_length) + "-" + to_string(sec) + "-P"
            + to_string(P.my_num());
    try
    {
        ifstream file(filename);
        octetStream os;
        os.input(file);
        os.get(machine.extra_slack);
        params.unpack(os);
        FieldD.unpack(os);
        FieldD.init_field();
        check(P, machine);
    }
    catch (...)
    {
        cout << "Finding parameters for security " << sec << " and field size ~2^"
                << plaintext_length << endl;
        machine.extra_slack = generate_semi_setup(plaintext_length, sec, params, FieldD, true);
        check(P, machine);
        octetStream os;
        os.store(machine.extra_slack);
        params.pack(os);
        FieldD.pack(os);
        ofstream file(filename);
        os.output(file);
    }
    alpha = FieldD;
}

template <class FD>
void PairwiseSetup<FD>::check(Player& P, PairwiseMachine& machine)
{
    Bundle<octetStream> bundle(P);
    bundle.mine.store(machine.extra_slack);
    params.pack(bundle.mine);
    FieldD.hash(bundle.mine);
    P.Broadcast_Receive(bundle, true);
    for (auto& os : bundle)
        if (os != bundle.mine)
            throw runtime_error("mismatch of parameters among parties");
}

template <class FD>
void PairwiseSetup<FD>::covert_key_generation(Player& P,
        PairwiseMachine& machine, int num_runs)
{
    vector<SeededPRNG> G(num_runs);
    vector<AllCommitments> commits(num_runs, P);
    vector<FHE_KeyPair> my_keys(num_runs, {params, FieldD.get_prime()});
    Bundle<octetStream> pks(P);

    for (int i = 0; i < num_runs; i++)
    {
        my_keys[i].generate(G[i]);
        my_keys[i].pk.pack(pks.mine);
        commits[i].commit({SEED_SIZE, G[i].get_seed()});
    }

    P.Broadcast_Receive(pks);
    int challenge = GlobalPRNG(P).get_uint(num_runs);
    machine.sk = my_keys[challenge].sk;
    machine.pk = my_keys[challenge].pk;

    for (int i = 0; i < num_runs; i++)
        if (i != challenge)
            commits[i].open({SEED_SIZE, G[i].get_seed()});

    for (int i = 0; i < num_runs; i++)
    {
         for (int j = 0; j < P.num_players(); j++)
            if (j != P.my_num())
            {
                FHE_PK pk(params);
                pk.unpack(pks[j]);
                if (i == challenge)
                    machine.other_pks[j] = pk;
                else
                {
                    FHE_KeyPair pair(params, FieldD.get_prime());
                    PRNG prng(commits[i].messages[j]);
                    pair.generate(prng);
                    if (pair.pk != pk)
                        throw bad_keygen("covert pairwise key generation");
                }
            }
    }
}

template <class FD>
void PairwiseSetup<FD>::covert_mac_generation(Player& P,
        PairwiseMachine& machine, int num_runs)
{
    vector<const FHE_PK*> pks;
    for (auto& pk : machine.other_pks)
        pks.push_back(&pk);
    covert_generation(alpha, machine.enc_alphas, pks, &P, num_runs, Diagonal);
    alphai = alpha.element(0);
}

template <class FD>
void PairwiseSetup<FD>::set_alphai(T alphai)
{
    this->alphai = alphai;
    alpha.assign_constant(alphai);
}

template class PairwiseSetup<FFT_Data>;
template class PairwiseSetup<P2Data>;