poulpy/core/src/fourier_glwe.rs

use backend::{
    Backend, FFT64, MatZnxDftOps, MatZnxDftScratch, Module, ScalarZnxDftOps, Scratch, VecZnxAlloc, VecZnxBig, VecZnxBigAlloc,
    VecZnxBigOps, VecZnxBigScratch, VecZnxDft, VecZnxDftAlloc, VecZnxDftOps, ZnxZero,
};
use sampling::source::Source;

use crate::{GGSWCiphertext, GLWECiphertext, GLWEPlaintext, GLWESecret, GLWESwitchingKey, Infos, ScratchCore};

pub struct FourierGLWECiphertext<C, B: Backend> {
    pub data: VecZnxDft<C, B>,
    pub basek: usize,
    pub k: usize,
}

impl<B: Backend> FourierGLWECiphertext<Vec<u8>, B> {
    pub fn alloc(module: &Module<B>, basek: usize, k: usize, rank: usize) -> Self {
        Self {
            data: module.new_vec_znx_dft(rank + 1, k.div_ceil(basek)),
            basek: basek,
            k: k,
        }
    }

    pub fn bytes_of(module: &Module<B>, basek: usize, k: usize, rank: usize) -> usize {
        module.bytes_of_vec_znx_dft(rank + 1, k.div_ceil(basek))
    }
}

impl<T, B: Backend> Infos for FourierGLWECiphertext<T, B> {
    type Inner = VecZnxDft<T, B>;

    fn inner(&self) -> &Self::Inner {
        &self.data
    }

    fn basek(&self) -> usize {
        self.basek
    }

    fn k(&self) -> usize {
        self.k
    }
}

impl<T, B: Backend> FourierGLWECiphertext<T, B> {
    pub fn rank(&self) -> usize {
        self.cols() - 1
    }
}

impl FourierGLWECiphertext<Vec<u8>, FFT64> {
    #[allow(dead_code)]
    pub(crate) fn idft_scratch_space(module: &Module<FFT64>, basek: usize, k: usize) -> usize {
        module.bytes_of_vec_znx(1, k.div_ceil(basek))
            + (module.vec_znx_big_normalize_tmp_bytes() | module.vec_znx_idft_tmp_bytes())
    }

    pub fn encrypt_sk_scratch_space(module: &Module<FFT64>, basek: usize, k: usize, rank: usize) -> usize {
        module.bytes_of_vec_znx(rank + 1, k.div_ceil(basek)) + GLWECiphertext::encrypt_sk_scratch_space(module, basek, k)
    }

    pub fn decrypt_scratch_space(module: &Module<FFT64>, basek: usize, k: usize) -> usize {
        let size: usize = k.div_ceil(basek);
        (module.vec_znx_big_normalize_tmp_bytes()
            | module.bytes_of_vec_znx_dft(1, size)
            | (module.bytes_of_vec_znx_big(1, size) + module.vec_znx_idft_tmp_bytes()))
            + module.bytes_of_vec_znx_big(1, size)
    }

    pub fn keyswitch_scratch_space(
        module: &Module<FFT64>,
        basek: usize,
        k_out: usize,
        k_in: usize,
        k_ksk: usize,
        digits: usize,
        rank_in: usize,
        rank_out: usize,
    ) -> usize {
        GLWECiphertext::bytes_of(module, basek, k_out, rank_out)
            + GLWECiphertext::keyswitch_from_fourier_scratch_space(module, basek, k_out, k_in, k_ksk, digits, rank_in, rank_out)
    }

    pub fn keyswitch_inplace_scratch_space(
        module: &Module<FFT64>,
        basek: usize,
        k_out: usize,
        k_ksk: usize,
        digits: usize,
        rank: usize,
    ) -> usize {
        Self::keyswitch_scratch_space(module, basek, k_out, k_out, k_ksk, digits, rank, rank)
    }

    // WARNING TODO: UPDATE
    pub fn external_product_scratch_space(
        module: &Module<FFT64>,
        basek: usize,
        _k_out: usize,
        k_in: usize,
        k_ggsw: usize,
        digits: usize,
        rank: usize,
    ) -> usize {
        let ggsw_size: usize = k_ggsw.div_ceil(basek);
        let res_dft: usize = module.bytes_of_vec_znx_dft(rank + 1, ggsw_size);
        let in_size: usize = k_in.div_ceil(basek).div_ceil(digits);
        let ggsw_size: usize = k_ggsw.div_ceil(basek);
        let vmp: usize = module.bytes_of_vec_znx_dft(rank + 1, in_size)
            + module.vmp_apply_tmp_bytes(ggsw_size, in_size, in_size, rank + 1, rank + 1, ggsw_size);
        let res_small: usize = module.bytes_of_vec_znx(rank + 1, ggsw_size);
        let normalize: usize = module.vec_znx_big_normalize_tmp_bytes();
        res_dft + (vmp | (res_small + normalize))
    }

    pub fn external_product_inplace_scratch_space(
        module: &Module<FFT64>,
        basek: usize,
        k_out: usize,
        k_ggsw: usize,
        digits: usize,
        rank: usize,
    ) -> usize {
        Self::external_product_scratch_space(module, basek, k_out, k_out, k_ggsw, digits, rank)
    }
}

impl<DataSelf: AsMut<[u8]> + AsRef<[u8]>> FourierGLWECiphertext<DataSelf, FFT64> {
    pub fn encrypt_zero_sk<DataSk: AsRef<[u8]>>(
        &mut self,
        module: &Module<FFT64>,
        sk: &GLWESecret<DataSk, FFT64>,
        source_xa: &mut Source,
        source_xe: &mut Source,
        sigma: f64,
        scratch: &mut Scratch,
    ) {
        let (mut tmp_ct, scratch1) = scratch.tmp_glwe_ct(module, self.basek(), self.k(), self.rank());
        tmp_ct.encrypt_zero_sk(module, sk, source_xa, source_xe, sigma, scratch1);
        tmp_ct.dft(module, self);
    }

    pub fn keyswitch<DataLhs: AsRef<[u8]>, DataRhs: AsRef<[u8]>>(
        &mut self,
        module: &Module<FFT64>,
        lhs: &FourierGLWECiphertext<DataLhs, FFT64>,
        rhs: &GLWESwitchingKey<DataRhs, FFT64>,
        scratch: &mut Scratch,
    ) {
        let (mut tmp_ct, scratch1) = scratch.tmp_glwe_ct(module, self.basek(), self.k(), self.rank());
        tmp_ct.keyswitch_from_fourier(module, lhs, rhs, scratch1);
        tmp_ct.dft(module, self);
    }

    pub fn keyswitch_inplace<DataRhs: AsRef<[u8]>>(
        &mut self,
        module: &Module<FFT64>,
        rhs: &GLWESwitchingKey<DataRhs, FFT64>,
        scratch: &mut Scratch,
    ) {
        unsafe {
            let self_ptr: *mut FourierGLWECiphertext<DataSelf, FFT64> = self as *mut FourierGLWECiphertext<DataSelf, FFT64>;
            self.keyswitch(&module, &*self_ptr, rhs, scratch);
        }
    }

    pub fn external_product<DataLhs: AsRef<[u8]>, DataRhs: AsRef<[u8]>>(
        &mut self,
        module: &Module<FFT64>,
        lhs: &FourierGLWECiphertext<DataLhs, FFT64>,
        rhs: &GGSWCiphertext<DataRhs, FFT64>,
        scratch: &mut Scratch,
    ) {
        let basek: usize = self.basek();

        #[cfg(debug_assertions)]
        {
            assert_eq!(rhs.rank(), lhs.rank());
            assert_eq!(rhs.rank(), self.rank());
            assert_eq!(self.basek(), basek);
            assert_eq!(lhs.basek(), basek);
            assert_eq!(rhs.n(), module.n());
            assert_eq!(self.n(), module.n());
            assert_eq!(lhs.n(), module.n());
            assert!(
                scratch.available()
                    >= FourierGLWECiphertext::external_product_scratch_space(
                        module,
                        self.basek(),
                        self.k(),
                        lhs.k(),
                        rhs.k(),
                        rhs.digits(),
                        rhs.rank(),
                    )
            );
        }

        let cols: usize = rhs.rank() + 1;
        let digits = rhs.digits();

        // Space for VMP result in DFT domain and high precision
        let (mut res_dft, scratch1) = scratch.tmp_vec_znx_dft(module, cols, rhs.size());
        let (mut a_dft, scratch2) = scratch1.tmp_vec_znx_dft(module, cols, (lhs.size() + digits - 1) / digits);

        {
            (0..digits).for_each(|di| {
                a_dft.set_size((lhs.size() + di) / digits);

                // Small optimization for digits > 2
                // VMP produce some error e, and since we aggregate vmp * 2^{di * B}, then
                // we also aggregate ei * 2^{di * B}, with the largest error being ei * 2^{(digits-1) * B}.
                // As such we can ignore the last digits-2 limbs safely of the sum of vmp products.
                // It is possible to further ignore the last digits-1 limbs, but this introduce
                // ~0.5 to 1 bit of additional noise, and thus not chosen here to ensure that the same
                // noise is kept with respect to the ideal functionality.
                res_dft.set_size(rhs.size() - ((digits - di) as isize - 2).max(0) as usize);

                (0..cols).for_each(|col_i| {
                    module.vec_znx_dft_copy(digits, digits - 1 - di, &mut a_dft, col_i, &lhs.data, col_i);
                });

                if di == 0 {
                    module.vmp_apply(&mut res_dft, &a_dft, &rhs.data, scratch2);
                } else {
                    module.vmp_apply_add(&mut res_dft, &a_dft, &rhs.data, di, scratch2);
                }
            });
        }

        // VMP result in high precision
        let res_big: VecZnxBig<&mut [u8], FFT64> = module.vec_znx_idft_consume::<&mut [u8]>(res_dft);

        // Space for VMP result normalized
        let (mut res_small, scratch2) = scratch1.tmp_vec_znx(module, cols, rhs.size());
        (0..cols).for_each(|i| {
            module.vec_znx_big_normalize(basek, &mut res_small, i, &res_big, i, scratch2);
            module.vec_znx_dft(1, 0, &mut self.data, i, &res_small, i);
        });
    }

    pub fn external_product_inplace<DataRhs: AsRef<[u8]>>(
        &mut self,
        module: &Module<FFT64>,
        rhs: &GGSWCiphertext<DataRhs, FFT64>,
        scratch: &mut Scratch,
    ) {
        unsafe {
            let self_ptr: *mut FourierGLWECiphertext<DataSelf, FFT64> = self as *mut FourierGLWECiphertext<DataSelf, FFT64>;
            self.external_product(&module, &*self_ptr, rhs, scratch);
        }
    }
}

impl<DataSelf: AsRef<[u8]>> FourierGLWECiphertext<DataSelf, FFT64> {
    pub fn decrypt<DataPt: AsRef<[u8]> + AsMut<[u8]>, DataSk: AsRef<[u8]>>(
        &self,
        module: &Module<FFT64>,
        pt: &mut GLWEPlaintext<DataPt>,
        sk: &GLWESecret<DataSk, FFT64>,
        scratch: &mut Scratch,
    ) {
        #[cfg(debug_assertions)]
        {
            assert_eq!(self.rank(), sk.rank());
            assert_eq!(self.n(), module.n());
            assert_eq!(pt.n(), module.n());
            assert_eq!(sk.n(), module.n());
        }

        let cols = self.rank() + 1;

        let (mut pt_big, scratch_1) = scratch.tmp_vec_znx_big(module, 1, self.size()); // TODO optimize size when pt << ct
        pt_big.zero();

        {
            (1..cols).for_each(|i| {
                let (mut ci_dft, _) = scratch_1.tmp_vec_znx_dft(module, 1, self.size()); // TODO optimize size when pt << ct
                module.svp_apply(&mut ci_dft, 0, &sk.data_fourier, i - 1, &self.data, i);
                let ci_big: VecZnxBig<&mut [u8], FFT64> = module.vec_znx_idft_consume(ci_dft);
                module.vec_znx_big_add_inplace(&mut pt_big, 0, &ci_big, 0);
            });
        }

        {
            let (mut c0_big, scratch_2) = scratch_1.tmp_vec_znx_big(module, 1, self.size());
            // c0_big = (a * s) + (-a * s + m + e) = BIG(m + e)
            module.vec_znx_idft(&mut c0_big, 0, &self.data, 0, scratch_2);
            module.vec_znx_big_add_inplace(&mut pt_big, 0, &c0_big, 0);
        }

        // pt = norm(BIG(m + e))
        module.vec_znx_big_normalize(self.basek(), &mut pt.data, 0, &mut pt_big, 0, scratch_1);

        pt.basek = self.basek();
        pt.k = pt.k().min(self.k());
    }

    #[allow(dead_code)]
    pub(crate) fn idft<DataRes: AsRef<[u8]> + AsMut<[u8]>>(
        &self,
        module: &Module<FFT64>,
        res: &mut GLWECiphertext<DataRes>,
        scratch: &mut Scratch,
    ) {
        #[cfg(debug_assertions)]
        {
            assert_eq!(self.rank(), res.rank());
            assert_eq!(self.basek(), res.basek())
        }

        let min_size: usize = self.size().min(res.size());

        let (mut res_big, scratch1) = scratch.tmp_vec_znx_big(module, 1, min_size);

        (0..self.rank() + 1).for_each(|i| {
            module.vec_znx_idft(&mut res_big, 0, &self.data, i, scratch1);
            module.vec_znx_big_normalize(self.basek(), &mut res.data, i, &res_big, 0, scratch1);
        });
    }
}