SealPIR/src/pir.hpp

#pragma once

#include "seal/seal.h"
#include "seal/util/polyarithsmallmod.h"
#include <cassert>
#include <cmath>
#include <string>
#include <vector>

typedef std::vector<seal::Plaintext> Database;
typedef std::vector<std::vector<seal::Ciphertext>> PirQuery;
typedef std::vector<seal::Ciphertext> PirReply;

struct PirParams {
    bool enable_symmetric;
    bool enable_batching;
    bool enable_mswitching;
    std::uint64_t ele_num;
    std::uint64_t ele_size;
    std::uint64_t elements_per_plaintext;
    std::uint64_t num_of_plaintexts;         // number of plaintexts in database
    std::uint32_t d;                         // number of dimensions for the database
    std::uint32_t expansion_ratio;           // ratio of ciphertext to plaintext
    std::vector<std::uint64_t> nvec;         // size of each of the d dimensions
    std::uint32_t slot_count;
};

void gen_encryption_params(std::uint32_t N,        // degree of polynomial
                           std::uint32_t logt,     // bits of plaintext coefficient
                           seal::EncryptionParameters &enc_params);

void gen_pir_params(uint64_t ele_num,
                    uint64_t ele_size,
                    uint32_t d,
                    const seal::EncryptionParameters &enc_params,
                    PirParams &pir_params,
                    bool enable_symmetric = false,
                    bool enable_batching = true,
                    bool enable_mswitching = true);

void gen_params(uint64_t ele_num,
                uint64_t ele_size,
                uint32_t N,
                uint32_t logt,
                uint32_t d,
                seal::EncryptionParameters &params,
                PirParams &pir_params);

void verify_encryption_params(const seal::EncryptionParameters &enc_params);

void print_pir_params(const PirParams &pir_params);
void print_seal_params(const seal::EncryptionParameters &enc_params);

// returns the number of plaintexts that the database can hold
std::uint64_t plaintexts_per_db(std::uint32_t logt, std::uint64_t N, std::uint64_t ele_num,
                                std::uint64_t ele_size);

// returns the number of elements that a single FV plaintext can hold
std::uint64_t elements_per_ptxt(std::uint32_t logt, std::uint64_t N, std::uint64_t ele_size);

// returns the number of coefficients needed to store one element
std::uint64_t coefficients_per_element(std::uint32_t logt, std::uint64_t ele_size);

// Converts an array of bytes to a vector of coefficients, each of which is less
// than the plaintext modulus
std::vector<std::uint64_t> bytes_to_coeffs(std::uint32_t limit, const std::uint8_t *bytes,
                                           std::uint64_t size);

// Converts an array of coefficients into an array of bytes
void coeffs_to_bytes(std::uint32_t limit, const std::vector<std::uint64_t> &coeffs, std::uint8_t *output, 
                    std::uint32_t size_out, std::uint32_t ele_size);

// Takes a vector of coefficients and returns the corresponding FV plaintext
void vector_to_plaintext(const std::vector<std::uint64_t> &coeffs, seal::Plaintext &plain);

// Since the database has d dimensions, and an item is a particular cell
// in the d-dimensional hypercube, this function computes the corresponding
// index for each of the d dimensions
std::vector<std::uint64_t> compute_indices(std::uint64_t desiredIndex,
                                           std::vector<std::uint64_t> nvec);

uint64_t invert_mod(uint64_t m, const seal::Modulus& mod);

uint32_t compute_expansion_ratio(seal::EncryptionParameters params);
std::vector<seal::Plaintext> decompose_to_plaintexts(seal::EncryptionParameters params,
    const seal::Ciphertext& ct);

//We need the returned ciphertext to be initialized by Context so the caller will pass it in
void compose_to_ciphertext(seal::EncryptionParameters params, 
    const std::vector<seal::Plaintext>& pts, seal::Ciphertext& ct);
void compose_to_ciphertext(seal::EncryptionParameters params, 
    std::vector<seal::Plaintext>::const_iterator pt_iter, seal::Ciphertext& ct);


// Serialize and deserialize galois keys to send them over the network
std::string serialize_galoiskeys(seal::Serializable<seal::GaloisKeys> g);
seal::GaloisKeys *deserialize_galoiskeys(std::string s, std::shared_ptr<seal::SEALContext> context);