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pir_client.cpp
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pir_client.cpp
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#include "pir_client.hpp"
using namespace std;
using namespace seal;
using namespace seal::util;
PIRClient::PIRClient(const EncryptionParameters ¶ms,
const EncryptionParameters &expanded_params, const PirParams &pir_parms) {
params_ = params;
SEALContext context(params);
expanded_params_ = expanded_params;
SEALContext newcontext(expanded_params);
pir_params_ = pir_parms;
keygen_.reset(new KeyGenerator(context));
encryptor_.reset(new Encryptor(context, keygen_->public_key()));
SecretKey secret_key = keygen_->secret_key();
secret_key.mutable_hash_block() = expanded_params.hash_block();
decryptor_.reset(new Decryptor(newcontext, secret_key));
evaluator_.reset(new Evaluator(newcontext));
}
void PIRClient::update_parameters(const EncryptionParameters &expanded_params,
const PirParams &pir_params) {
// The only thing that can change is the plaintext modulus and pir_params
assert(expanded_params.poly_modulus() == expanded_params_.poly_modulus());
assert(expanded_params.coeff_modulus() == expanded_params_.coeff_modulus());
expanded_params_ = expanded_params;
pir_params_ = pir_params;
SEALContext newcontext(expanded_params);
SecretKey secret_key = keygen_->secret_key();
secret_key.mutable_hash_block() = expanded_params.hash_block();
decryptor_.reset(new Decryptor(newcontext, secret_key));
evaluator_.reset(new Evaluator(newcontext));
}
PirQuery PIRClient::generate_query(uint64_t desiredIndex) {
vector<uint64_t> indices = compute_indices(desiredIndex, pir_params_.nvec);
vector<Ciphertext> result;
for (uint32_t i = 0; i < indices.size(); i++) {
Ciphertext dest;
encryptor_->encrypt(Plaintext("1x^" + std::to_string(indices[i])), dest);
dest.mutable_hash_block() = expanded_params_.hash_block();
result.push_back(dest);
}
return result;
}
uint64_t PIRClient::get_fv_index(uint64_t element_idx, uint64_t ele_size) {
uint32_t N = params_.poly_modulus().coeff_count() - 1;
uint32_t logtp = ceil(log2(expanded_params_.plain_modulus().value()));
uint64_t ele_per_ptxt = elements_per_ptxt(logtp, N, ele_size);
return element_idx / ele_per_ptxt;
}
uint64_t PIRClient::get_fv_offset(uint64_t element_idx, uint64_t ele_size) {
uint32_t N = params_.poly_modulus().coeff_count() - 1;
uint32_t logtp = ceil(log2(expanded_params_.plain_modulus().value()));
uint64_t ele_per_ptxt = elements_per_ptxt(logtp, N, ele_size);
return element_idx % ele_per_ptxt;
}
Plaintext PIRClient::decode_reply(PirReply reply) {
uint32_t exp_ratio = pir_params_.expansion_ratio;
uint32_t recursion_level = pir_params_.d;
vector<Ciphertext> temp = reply;
for (uint32_t i = 0; i < recursion_level; i++) {
vector<Ciphertext> newtemp;
vector<Plaintext> tempplain;
for (uint32_t j = 0; j < temp.size(); j++) {
Plaintext ptxt;
decryptor_->decrypt(temp[j], ptxt);
tempplain.push_back(ptxt);
#ifdef DEBUG
cout << "recursion level : " << i << " noise budget : ";
cout << decryptor_->invariant_noise_budget(temp[j]) << endl;
#endif
if ((j + 1) % exp_ratio == 0 && j > 0) {
// Combine into one ciphertext.
Ciphertext combined = compose_to_ciphertext(tempplain);
newtemp.push_back(combined);
}
}
if (i == recursion_level - 1) {
assert(temp.size() == 1);
return tempplain[0];
} else {
tempplain.clear();
temp = newtemp;
}
}
// This should never be called
assert(0);
Plaintext fail;
return fail;
}
GaloisKeys PIRClient::generate_galois_keys() {
// Generate the Galois keys needed for coeff_select.
vector<uint64_t> galois_elts;
int N = params_.poly_modulus().coeff_count() - 1;
int logN = get_power_of_two(N);
for (int i = 0; i < logN; i++) {
galois_elts.push_back((N + exponentiate_uint64(2, i)) / exponentiate_uint64(2, i));
#ifdef DEBUG
cout << galois_elts.back() << ", ";
#endif
}
GaloisKeys galois_keys;
keygen_->generate_galois_keys(pir_params_.dbc, galois_elts, galois_keys);
return galois_keys;
}
Ciphertext PIRClient::compose_to_ciphertext(vector<Plaintext> plains) {
int encrypted_count = 2;
int coeff_count = expanded_params_.poly_modulus().coeff_count();
int coeff_mod_count = expanded_params_.coeff_modulus().size();
uint64_t plainMod = expanded_params_.plain_modulus().value();
Ciphertext result;
result.reserve(expanded_params_, encrypted_count);
// A triple for loop. Going over polys, moduli, and decomposed index.
for (int i = 0; i < encrypted_count; i++) {
uint64_t *encrypted_pointer = result.mutable_pointer(i);
for (int j = 0; j < coeff_mod_count; j++) {
// populate one poly at a time.
// create a polynomial to store the current decomposition value
// which will be copied into the array to populate it at the current
// index.
double logqj = log2(expanded_params_.coeff_modulus()[j].value());
int expansion_ratio = ceil(logqj / log2(plainMod));
// cout << "expansion ratio = " << expansion_ratio << endl;
uint64_t cur = 1;
for (int k = 0; k < expansion_ratio; k++) {
// Compose here
const uint64_t *plain_coeff =
plains[k + j * (expansion_ratio) + i * (coeff_mod_count * expansion_ratio)]
.pointer();
for (int m = 0; m < coeff_count - 1; m++) {
if (k == 0) {
*(encrypted_pointer + m + j * coeff_count) = *(plain_coeff + m) * cur;
} else {
*(encrypted_pointer + m + j * coeff_count) += *(plain_coeff + m) * cur;
}
}
*(encrypted_pointer + coeff_count - 1 + j * coeff_count) = 0;
cur *= plainMod;
}
// XXX: Reduction modulo qj. This is needed?
/*
for (int m = 0; m < coeff_count; m++) {
*(encrypted_pointer + m + j * coeff_count) %=
expanded_params_.coeff_modulus()[j].value();
}
*/
}
}
result.mutable_hash_block() = expanded_params_.hash_block();
return result;
}