forked from tuneinsight/lattigo
/
encoder.go
347 lines (275 loc) · 10.6 KB
/
encoder.go
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package bgv
import (
"math/big"
"github.com/fedejinich/lattigo/v6/ring"
"github.com/fedejinich/lattigo/v6/rlwe"
"github.com/fedejinich/lattigo/v6/utils"
)
// GaloisGen is an integer of order N=2^d modulo M=2N and that spans Z_M with the integer -1.
// The j-th ring automorphism takes the root zeta to zeta^(5j).
const GaloisGen uint64 = ring.GaloisGen
// Encoder is an interface for plaintext encoding and decoding operations.
// It provides methods to embed []uint64 and []int64 types into plaintext
// polynomials and the inverse operations.
type Encoder interface {
Encode(values interface{}, pt *rlwe.Plaintext)
EncodeNew(values interface{}, level int, scale rlwe.Scale) (pt *rlwe.Plaintext)
EncodeCoeffs(values []uint64, pt *rlwe.Plaintext)
EncodeCoeffsNew(values []uint64, level int, scale rlwe.Scale) (pt *rlwe.Plaintext)
RingT2Q(level int, pT, pQ *ring.Poly)
RingQ2T(level int, pQ, pT *ring.Poly)
ScaleUp(level int, pIn, pOut *ring.Poly)
ScaleDown(level int, pIn, pOut *ring.Poly)
EncodeRingT(values interface{}, scale rlwe.Scale, pT *ring.Poly)
DecodeRingT(pT *ring.Poly, scale rlwe.Scale, values interface{})
DecodeUint(pt *rlwe.Plaintext, values []uint64)
DecodeInt(pt *rlwe.Plaintext, values []int64)
DecodeUintNew(pt *rlwe.Plaintext) (values []uint64)
DecodeIntNew(pt *rlwe.Plaintext) (values []int64)
DecodeCoeffs(pt *rlwe.Plaintext, values []uint64)
DecodeCoeffsNew(pt *rlwe.Plaintext) (values []uint64)
ShallowCopy() Encoder
}
// encoder is a structure that stores the parameters to encode values on a plaintext in a SIMD (Single-Instruction Multiple-Data) fashion.
type encoder struct {
params Parameters
indexMatrix []uint64
buffQ *ring.Poly
buffT *ring.Poly
paramsQP []ring.ModUpConstants
qHalf []*big.Int
tInvModQ []*big.Int
}
// NewEncoder creates a new encoder from the provided parameters.
func NewEncoder(params Parameters) Encoder {
var N, logN, pow, pos uint64 = uint64(params.N()), uint64(params.LogN()), 1, 0
mask := 2*N - 1
indexMatrix := make([]uint64, N)
for i, j := 0, int(N>>1); i < int(N>>1); i, j = i+1, j+1 {
pos = utils.BitReverse64(pow>>1, logN)
indexMatrix[i] = pos
indexMatrix[j] = N - pos - 1
pow *= GaloisGen
pow &= mask
}
ringQ := params.RingQ()
ringT := params.RingT()
paramsQP := make([]ring.ModUpConstants, ringQ.ModuliChainLength())
qHalf := make([]*big.Int, ringQ.ModuliChainLength())
moduli := ringQ.ModuliChain()
T := ringT.SubRings[0].Modulus
for i := 1; i < ringQ.ModuliChainLength(); i++ {
paramsQP[i] = ring.GenModUpConstants(moduli[:i+1], []uint64{T})
qHalf[i] = new(big.Int).Set(ringQ.ModulusAtLevel[i])
qHalf[i].Rsh(qHalf[i], 1)
}
tInvModQ := make([]*big.Int, ringQ.ModuliChainLength())
for i := range moduli {
tInvModQ[i] = ring.NewUint(T)
tInvModQ[i].ModInverse(tInvModQ[i], ringQ.ModulusAtLevel[i])
}
return &encoder{
params: params,
indexMatrix: indexMatrix,
buffQ: ringQ.NewPoly(),
buffT: ringT.NewPoly(),
paramsQP: paramsQP,
qHalf: qHalf,
tInvModQ: tInvModQ,
}
}
// EncodeNew encodes a slice of integers of type []uint64 or []int64 of size at most N on a newly allocated plaintext.
func (ecd *encoder) EncodeNew(values interface{}, level int, scale rlwe.Scale) (pt *rlwe.Plaintext) {
pt = NewPlaintext(ecd.params, level)
pt.Scale = scale
ecd.Encode(values, pt)
return
}
// Encode encodes a slice of integers of type []uint64 or []int64 of size at most N into a pre-allocated plaintext.
func (ecd *encoder) Encode(values interface{}, pt *rlwe.Plaintext) {
ecd.EncodeRingT(values, pt.Scale, ecd.buffT)
ecd.RingT2Q(pt.Level(), ecd.buffT, pt.Value)
if pt.IsNTT {
ecd.params.RingQ().AtLevel(pt.Level()).NTT(pt.Value, pt.Value)
}
ecd.ScaleUp(pt.Level(), pt.Value, pt.Value)
}
// EncodeCoeffs encodes a slice of []uint64 of size at most N on a pre-allocated plaintext.
// The encoding is done coefficient wise, i.e. [1, 2, 3, 4] -> 1 + 2X + 3X^2 + 4X^3.
func (ecd *encoder) EncodeCoeffs(values []uint64, pt *rlwe.Plaintext) {
copy(ecd.buffT.Coeffs[0], values)
for i := len(values); i < len(ecd.buffT.Coeffs[0]); i++ {
ecd.buffT.Coeffs[0][i] = 0
}
ringT := ecd.params.RingT()
ringT.MulScalar(ecd.buffT, pt.Scale.Uint64(), ecd.buffT)
ecd.RingT2Q(pt.Level(), ecd.buffT, pt.Value)
if pt.IsNTT {
ecd.params.RingQ().AtLevel(pt.Level()).NTT(pt.Value, pt.Value)
}
ecd.ScaleUp(pt.Level(), pt.Value, pt.Value)
}
// EncodeCoeffsNew encodes a slice of []uint64 of size at most N on a newly allocated plaintext.
// The encoding is done coefficient wise, i.e. [1, 2, 3, 4] -> 1 + 2X + 3X^2 + 4X^3.}
func (ecd *encoder) EncodeCoeffsNew(values []uint64, level int, scale rlwe.Scale) (pt *rlwe.Plaintext) {
pt = NewPlaintext(ecd.params, level)
pt.Scale = scale
ecd.EncodeCoeffs(values, pt)
return
}
// EncodeRingT encodes a slice of []uint64 or []int64 on a polynomial in basis T.
func (ecd *encoder) EncodeRingT(values interface{}, scale rlwe.Scale, pT *ring.Poly) {
if len(pT.Coeffs[0]) != len(ecd.indexMatrix) {
panic("cannot EncodeRingT: invalid plaintext to receive encoding: number of coefficients does not match the ring degree")
}
pt := pT.Coeffs[0]
ringT := ecd.params.RingT()
var valLen int
switch values := values.(type) {
case []uint64:
for i, c := range values {
pt[ecd.indexMatrix[i]] = c
}
ringT.Reduce(pT, pT)
valLen = len(values)
case []int64:
T := ringT.SubRings[0].Modulus
BRedConstantT := ringT.SubRings[0].BRedConstant
var sign, abs uint64
for i, c := range values {
sign = uint64(c) >> 63
abs = ring.BRedAdd(uint64(c*((int64(sign)^1)-int64(sign))), T, BRedConstantT)
pt[ecd.indexMatrix[i]] = sign*(T-abs) | (sign^1)*abs
}
valLen = len(values)
default:
panic("cannot EncodeRingT: values must be either []uint64 or []int64")
}
for i := valLen; i < len(ecd.indexMatrix); i++ {
pt[ecd.indexMatrix[i]] = 0
}
ringT.INTT(pT, pT)
ringT.MulScalar(pT, scale.Uint64(), pT)
}
// EncodeRingT decodes a pT in basis T on a slice of []uint64 or []int64.
func (ecd *encoder) DecodeRingT(pT *ring.Poly, scale rlwe.Scale, values interface{}) {
ringT := ecd.params.RingT()
ringT.MulScalar(pT, ring.ModExp(scale.Uint64(), ringT.SubRings[0].Modulus-2, ringT.SubRings[0].Modulus), ecd.buffT)
ringT.NTT(ecd.buffT, ecd.buffT)
tmp := ecd.buffT.Coeffs[0]
N := ecd.params.N()
switch values := values.(type) {
case []uint64:
for i := 0; i < N; i++ {
values[i] = tmp[ecd.indexMatrix[i]]
}
case []int64:
modulus := int64(ecd.params.T())
modulusHalf := modulus >> 1
var value int64
for i := 0; i < N; i++ {
if value = int64(tmp[ecd.indexMatrix[i]]); value >= modulusHalf {
values[i] = value - modulus
} else {
values[i] = value
}
}
default:
panic("cannot DecodeRingT: values must be either []uint64 or []int64")
}
}
// RingT2Q takes pT in base T and returns it in base Q on pQ.
func (ecd *encoder) RingT2Q(level int, pT, pQ *ring.Poly) {
for i := 0; i < level+1; i++ {
copy(pQ.Coeffs[i], pT.Coeffs[0])
}
}
// ScaleUp scales pIn up T^1 mod Q and returns the result in pOut.
func (ecd *encoder) ScaleUp(level int, pIn, pOut *ring.Poly) {
ecd.params.RingQ().AtLevel(level).MulScalarBigint(pIn, ecd.tInvModQ[level], pOut)
}
// RingQ2T takes pQ in base Q and returns it in base T on pT.
func (ecd *encoder) RingQ2T(level int, pQ, pT *ring.Poly) {
ringQ := ecd.params.RingQ().AtLevel(level)
ringT := ecd.params.RingT()
if level > 0 {
ringQ.AddScalarBigint(pQ, ecd.qHalf[level], ecd.buffQ)
ring.ModUpExact(ecd.buffQ.Coeffs[:level+1], pT.Coeffs, ringQ, ringT, ecd.paramsQP[level])
ringT.SubScalarBigint(pT, ecd.qHalf[level], pT)
} else {
ringQ.AddScalar(pQ, ringQ.SubRings[0].Modulus>>1, ecd.buffQ)
ringT.Reduce(ecd.buffQ, pT)
ringT.SubScalar(pT, ring.BRedAdd(ringQ.SubRings[0].Modulus>>1, ringT.SubRings[0].Modulus, ringT.SubRings[0].BRedConstant), pT)
}
}
// ScaleDown scales pIn down by T and returns the result in pOut.
func (ecd *encoder) ScaleDown(level int, pIn, pOut *ring.Poly) {
ecd.params.RingQ().AtLevel(level).MulScalar(pIn, ecd.params.T(), pOut)
}
// DecodeUint decodes a any plaintext type and write the coefficients on an pre-allocated uint64 slice.
func (ecd *encoder) DecodeUint(pt *rlwe.Plaintext, values []uint64) {
if pt.IsNTT {
ecd.params.RingQ().AtLevel(pt.Level()).INTT(pt.Value, ecd.buffQ)
ecd.ScaleDown(pt.Level(), ecd.buffQ, ecd.buffQ)
} else {
ecd.ScaleDown(pt.Level(), pt.Value, ecd.buffQ)
}
ecd.RingQ2T(pt.Level(), ecd.buffQ, ecd.buffT)
ecd.DecodeRingT(ecd.buffT, pt.Scale, values)
}
// DecodeUintNew decodes any plaintext type and returns the coefficients on a new []uint64 slice.
func (ecd *encoder) DecodeUintNew(pt *rlwe.Plaintext) (values []uint64) {
values = make([]uint64, ecd.params.N())
ecd.DecodeUint(pt, values)
return
}
// DecodeInt decodes a any plaintext type and write the coefficients on an pre-allocated int64 slice.
// Values are centered between [t/2, t/2).
func (ecd *encoder) DecodeInt(pt *rlwe.Plaintext, values []int64) {
if pt.IsNTT {
ecd.params.RingQ().AtLevel(pt.Level()).INTT(pt.Value, ecd.buffQ)
ecd.ScaleDown(pt.Level(), ecd.buffQ, ecd.buffQ)
} else {
ecd.ScaleDown(pt.Level(), pt.Value, ecd.buffQ)
}
ecd.RingQ2T(pt.Level(), ecd.buffQ, ecd.buffT)
ecd.DecodeRingT(ecd.buffT, pt.Scale, values)
}
// DecodeInt decodes a any plaintext type and write the coefficients on an new int64 slice.
// Values are centered between [t/2, t/2).
func (ecd *encoder) DecodeIntNew(pt *rlwe.Plaintext) (values []int64) {
values = make([]int64, ecd.params.N())
ecd.DecodeInt(pt, values)
return
}
func (ecd *encoder) DecodeCoeffs(pt *rlwe.Plaintext, values []uint64) {
if pt.IsNTT {
ecd.params.RingQ().AtLevel(pt.Level()).INTT(pt.Value, ecd.buffQ)
ecd.ScaleDown(pt.Level(), ecd.buffQ, ecd.buffQ)
} else {
ecd.ScaleDown(pt.Level(), pt.Value, ecd.buffQ)
}
ecd.RingQ2T(pt.Level(), ecd.buffQ, ecd.buffT)
ringT := ecd.params.RingT()
ringT.MulScalar(ecd.buffT, ring.ModExp(pt.Scale.Uint64(), ringT.SubRings[0].Modulus-2, ringT.SubRings[0].Modulus), ecd.buffT)
copy(values, ecd.buffT.Coeffs[0])
}
func (ecd *encoder) DecodeCoeffsNew(pt *rlwe.Plaintext) (values []uint64) {
values = make([]uint64, ecd.params.N())
ecd.DecodeCoeffs(pt, values)
return
}
// ShallowCopy creates a shallow copy of Encoder in which all the read-only data-structures are
// shared with the receiver and the temporary buffers are reallocated. The receiver and the returned
// Encoder can be used concurrently.
func (ecd *encoder) ShallowCopy() Encoder {
return &encoder{
params: ecd.params,
indexMatrix: ecd.indexMatrix,
buffQ: ecd.params.RingQ().NewPoly(),
buffT: ecd.params.RingT().NewPoly(),
paramsQP: ecd.paramsQP,
qHalf: ecd.qHalf,
tInvModQ: ecd.tInvModQ,
}
}