hestdparms.h

// Copyright (c) Microsoft Corporation. All rights reserved.
// Licensed under the MIT license.

#pragma once

#include "seal/util/defines.h"

namespace seal
{
    namespace util
    {
        /**
        Largest allowed bit counts for coeff_modulus based on the security estimates from
        HomomorphicEncryption.org security standard. Microsoft SEAL samples the secret key
        from a ternary {-1, 0, 1} distribution.
        */
        // Ternary secret; 128 bits classical security
        SEAL_NODISCARD constexpr int SEAL_HE_STD_PARMS_128_TC(
            std::size_t poly_modulus_degree) noexcept
        {
            switch (poly_modulus_degree)
            {
                case std::size_t(1024):      return 27;
                case std::size_t(2048):      return 54;
                case std::size_t(4096):      return 109;
                case std::size_t(8192):      return 218;
                case std::size_t(16384):     return 438;
                case std::size_t(32768):     return 881;
            }
            return 0;
        }

        // Ternary secret; 192 bits classical security
        SEAL_NODISCARD constexpr int SEAL_HE_STD_PARMS_192_TC(
            std::size_t poly_modulus_degree) noexcept
        {
            switch (poly_modulus_degree)
            {
                case std::size_t(1024):      return 19;
                case std::size_t(2048):      return 37;
                case std::size_t(4096):      return 75;
                case std::size_t(8192):      return 152;
                case std::size_t(16384):     return 305;
                case std::size_t(32768):     return 611;
            }
            return 0;
        }

        // Ternary secret; 256 bits classical security
        SEAL_NODISCARD constexpr int SEAL_HE_STD_PARMS_256_TC(
            std::size_t poly_modulus_degree) noexcept
        {
            switch (poly_modulus_degree)
            {
                case std::size_t(1024):      return 14;
                case std::size_t(2048):      return 29;
                case std::size_t(4096):      return 58;
                case std::size_t(8192):      return 118;
                case std::size_t(16384):     return 237;
                case std::size_t(32768):     return 476;
            }
            return 0;
        }

        // Ternary secret; 128 bits quantum security
        SEAL_NODISCARD constexpr int SEAL_HE_STD_PARMS_128_TQ(
            std::size_t poly_modulus_degree) noexcept
        {
            switch (poly_modulus_degree)
            {
                case std::size_t(1024):      return 25;
                case std::size_t(2048):      return 51;
                case std::size_t(4096):      return 101;
                case std::size_t(8192):      return 202;
                case std::size_t(16384):     return 411;
                case std::size_t(32768):     return 827;
            }
            return 0;
        }

        // Ternary secret; 192 bits quantum security
        SEAL_NODISCARD constexpr int SEAL_HE_STD_PARMS_192_TQ(
            std::size_t poly_modulus_degree) noexcept
        {
            switch (poly_modulus_degree)
            {
                case std::size_t(1024):      return 17;
                case std::size_t(2048):      return 35;
                case std::size_t(4096):      return 70;
                case std::size_t(8192):      return 141;
                case std::size_t(16384):     return 284;
                case std::size_t(32768):     return 571;
            }
            return 0;
        }

        // Ternary secret; 256 bits quantum security
        SEAL_NODISCARD constexpr int SEAL_HE_STD_PARMS_256_TQ(
            std::size_t poly_modulus_degree) noexcept
        {
            switch (poly_modulus_degree)
            {
                case std::size_t(1024):      return 13;
                case std::size_t(2048):      return 27;
                case std::size_t(4096):      return 54;
                case std::size_t(8192):      return 109;
                case std::size_t(16384):     return 220;
                case std::size_t(32768):     return 443;
            }
            return 0;
        }

        // Standard deviation for error distribution
        constexpr double SEAL_HE_STD_PARMS_ERROR_STD_DEV = 3.20;
    }
}