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keyswitch_sk.go
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keyswitch_sk.go
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package drlwe
import (
"github.com/jzhchu/lattigo/ring"
"github.com/jzhchu/lattigo/rlwe"
"github.com/jzhchu/lattigo/rlwe/ringqp"
"github.com/jzhchu/lattigo/utils"
)
// CKSProtocol is the structure storing the parameters and and precomputations for the collective key-switching protocol.
type CKSProtocol struct {
params rlwe.Parameters
sigmaSmudging float64
gaussianSampler *ring.GaussianSampler
basisExtender *ring.BasisExtender
tmpQP ringqp.Poly
tmpDelta *ring.Poly
}
type NizkCKSProtocol struct {
params rlwe.Parameters
sigmaSmudging float64
gaussianSampler *ring.GaussianSampler
basisExtender *ring.BasisExtender
tmpQP ringqp.Poly
tmpDelta *ring.Poly
e *ring.Poly
}
// ShallowCopy creates a shallow copy of CKSProtocol in which all the read-only data-structures are
// shared with the receiver and the temporary buffers are reallocated. The receiver and the returned
// CKSProtocol can be used concurrently.
func (cks *CKSProtocol) ShallowCopy() *CKSProtocol {
prng, err := utils.NewPRNG()
if err != nil {
panic(err)
}
params := cks.params
return &CKSProtocol{
params: params,
gaussianSampler: ring.NewGaussianSampler(prng, params.RingQ(), cks.sigmaSmudging, int(6*cks.sigmaSmudging)),
basisExtender: cks.basisExtender.ShallowCopy(),
tmpQP: params.RingQP().NewPoly(),
tmpDelta: params.RingQ().NewPoly(),
}
}
func (nizkCKS *NizkCKSProtocol) ShallowCopy() *NizkCKSProtocol {
prng, err := utils.NewPRNG()
if err != nil {
panic(err)
}
params := nizkCKS.params
var eTemp *ring.Poly
eTemp.Copy(nizkCKS.e)
return &NizkCKSProtocol{
params: params,
gaussianSampler: ring.NewGaussianSampler(prng, params.RingQ(), nizkCKS.sigmaSmudging, int(6*nizkCKS.sigmaSmudging)),
basisExtender: nizkCKS.basisExtender.ShallowCopy(),
tmpQP: params.RingQP().NewPoly(),
tmpDelta: params.RingQ().NewPoly(),
e: eTemp,
}
}
// CKSShare is a type for the CKS protocol shares.
type CKSShare struct {
Value *ring.Poly
}
// CKSCRP is a type for common reference polynomials in the CKS protocol.
type CKSCRP ring.Poly
// MarshalBinary encodes a CKS share on a slice of bytes.
func (ckss *CKSShare) MarshalBinary() (data []byte, err error) {
return ckss.Value.MarshalBinary()
}
// UnmarshalBinary decodes marshaled CKS share on the target CKS share.
func (ckss *CKSShare) UnmarshalBinary(data []byte) (err error) {
ckss.Value = new(ring.Poly)
return ckss.Value.UnmarshalBinary(data)
}
// NewCKSProtocol creates a new CKSProtocol that will be used to perform a collective key-switching on a ciphertext encrypted under a collective public-key, whose
// secret-shares are distributed among j parties, re-encrypting the ciphertext under another public-key, whose secret-shares are also known to the
// parties.
func NewCKSProtocol(params rlwe.Parameters, sigmaSmudging float64) *CKSProtocol {
cks := new(CKSProtocol)
cks.params = params
cks.sigmaSmudging = sigmaSmudging
prng, err := utils.NewPRNG()
if err != nil {
panic(err)
}
cks.gaussianSampler = ring.NewGaussianSampler(prng, params.RingQ(), sigmaSmudging, int(6*sigmaSmudging))
if cks.params.RingP() != nil {
cks.basisExtender = ring.NewBasisExtender(params.RingQ(), params.RingP())
}
cks.tmpQP = params.RingQP().NewPoly()
cks.tmpDelta = params.RingQ().NewPoly()
return cks
}
// AllocateShare allocates the shares of the CKSProtocol
func (cks *CKSProtocol) AllocateShare(level int) *CKSShare {
return &CKSShare{cks.params.RingQ().NewPolyLvl(level)}
}
// SampleCRP samples a common random polynomial to be used in the CKS protocol from the provided
// common reference string.
func (cks *CKSProtocol) SampleCRP(level int, crs CRS) CKSCRP {
crp := cks.params.RingQ().NewPolyLvl(level)
ring.NewUniformSampler(crs, cks.params.RingQ()).ReadLvl(level, crp)
return CKSCRP(*crp)
}
// GenShare computes a party's share in the CKS protocol from secret-key skInput to secret-key skOutput.
// ct is the rlwe.Ciphertext to keyswitch. Note that ct.Value[0] is not used by the function and can be nil/zero.
func (cks *CKSProtocol) GenShare(skInput, skOutput *rlwe.SecretKey, ct *rlwe.Ciphertext, shareOut *CKSShare) {
ringQ := cks.params.RingQ()
ringP := cks.params.RingP()
ringQP := cks.params.RingQP()
c1 := ct.Value[1]
levelQ := utils.MinInt(shareOut.Value.Level(), c1.Level())
levelP := cks.params.PCount() - 1
ringQ.SubLvl(levelQ, skInput.Value.Q, skOutput.Value.Q, cks.tmpDelta)
ct1 := c1
if !ct.IsNTT {
ringQ.NTTLazyLvl(levelQ, c1, cks.tmpQP.Q)
ct1 = cks.tmpQP.Q
}
// a * (skIn - skOut) mod Q
ringQ.MulCoeffsMontgomeryConstantLvl(levelQ, ct1, cks.tmpDelta, shareOut.Value)
if ringP != nil {
// P * a * (skIn - skOut) mod QP (mod P = 0)
ringQ.MulScalarBigintLvl(levelQ, shareOut.Value, ringP.ModulusAtLevel[levelP], shareOut.Value)
}
if !ct.IsNTT {
// InvNTT(P * a * (skIn - skOut)) mod QP (mod P = 0)
ringQ.InvNTTLazyLvl(levelQ, shareOut.Value, shareOut.Value)
// Samples e in Q
cks.gaussianSampler.ReadLvl(levelQ, cks.tmpQP.Q)
if ringP != nil {
// Extend e to P (assumed to have norm < qi)
ringQP.ExtendBasisSmallNormAndCenter(cks.tmpQP.Q, levelP, nil, cks.tmpQP.P)
}
// InvNTT(P * a * (skIn - skOut) + e) mod QP (mod P = e)
ringQ.AddLvl(levelQ, shareOut.Value, cks.tmpQP.Q, shareOut.Value)
if ringP != nil {
// InvNTT(P * a * (skIn - skOut) + e) * (1/P) mod QP (mod P = e)
cks.basisExtender.ModDownQPtoQ(levelQ, levelP, shareOut.Value, cks.tmpQP.P, shareOut.Value)
}
} else {
// Sample e in Q
cks.gaussianSampler.ReadLvl(levelQ, cks.tmpQP.Q)
if ringP != nil {
// Extend e to P (assumed to have norm < qi)
ringQP.ExtendBasisSmallNormAndCenter(cks.tmpQP.Q, levelP, nil, cks.tmpQP.P)
}
// Takes the error to the NTT domain
ringQ.InvNTTLvl(levelQ, shareOut.Value, shareOut.Value)
// P * a * (skIn - skOut) + e mod Q (mod P = 0, so P = e)
ringQ.AddLvl(levelQ, shareOut.Value, cks.tmpQP.Q, shareOut.Value)
if ringP != nil {
// (P * a * (skIn - skOut) + e) * (1/P) mod QP (mod P = e)
cks.basisExtender.ModDownQPtoQ(levelQ, levelP, shareOut.Value, cks.tmpQP.P, shareOut.Value)
}
ringQ.NTTLvl(levelQ, shareOut.Value, shareOut.Value)
}
shareOut.Value.Resize(levelQ)
}
// AggregateShares is the second part of the unique round of the CKSProtocol protocol. Upon receiving the j-1 elements each party computes :
//
// [ctx[0] + sum((skInput_i - skOutput_i) * ctx[0] + e_i), ctx[1]]
func (cks *CKSProtocol) AggregateShares(share1, share2, shareOut *CKSShare) {
cks.params.RingQ().AddLvl(share1.Value.Level(), share1.Value, share2.Value, shareOut.Value)
}
// KeySwitch performs the actual keyswitching operation on a ciphertext ct and put the result in ctOut
func (cks *CKSProtocol) KeySwitch(ctIn *rlwe.Ciphertext, combined *CKSShare, ctOut *rlwe.Ciphertext) {
level := ctIn.Level()
if ctIn != ctOut {
ctOut.Resize(ctIn.Degree(), level)
ring.CopyLvl(level, ctIn.Value[1], ctOut.Value[1])
ctOut.MetaData = ctIn.MetaData
}
cks.params.RingQ().AddLvl(level, ctIn.Value[0], combined.Value, ctOut.Value[0])
}
func NewNizkCKSProtocol(params rlwe.Parameters, sigmaSmudging float64) *NizkCKSProtocol {
nizkCKS := new(NizkCKSProtocol)
nizkCKS.params = params
nizkCKS.sigmaSmudging = sigmaSmudging
prng, err := utils.NewPRNG()
if err != nil {
panic(err)
}
nizkCKS.gaussianSampler = ring.NewGaussianSampler(prng, params.RingQ(), sigmaSmudging, int(6*sigmaSmudging))
if nizkCKS.params.RingP() != nil {
nizkCKS.basisExtender = ring.NewBasisExtender(params.RingQ(), params.RingP())
}
nizkCKS.tmpQP = params.RingQP().NewPoly()
nizkCKS.tmpDelta = params.RingQ().NewPoly()
nizkCKS.e = params.RingQ().NewPoly()
return nizkCKS
}
func (nizkCKS *NizkCKSProtocol) AllocateShare(level int) *CKSShare {
return &CKSShare{nizkCKS.params.RingQ().NewPolyLvl(level)}
}
func (nizkCKS *NizkCKSProtocol) SampleCRP(level int, crs CRS) CKSCRP {
crp := nizkCKS.params.RingQ().NewPolyLvl(level)
ring.NewUniformSampler(crs, nizkCKS.params.RingQ()).ReadLvl(level, crp)
return CKSCRP(*crp)
}
func (nizkCKS *NizkCKSProtocol) GenShare(skInput, skOutput *rlwe.SecretKey, ct *rlwe.Ciphertext, shareOut *CKSShare) {
ringQ := nizkCKS.params.RingQ()
ringP := nizkCKS.params.RingP()
ringQP := nizkCKS.params.RingQP()
c1 := ct.Value[1]
levelQ := utils.MinInt(shareOut.Value.Level(), c1.Level())
levelP := nizkCKS.params.PCount() - 1
ringQ.SubLvl(levelQ, skInput.Value.Q, skOutput.Value.Q, nizkCKS.tmpDelta)
ct1 := c1
if !ct.IsNTT {
ringQ.NTTLazyLvl(levelQ, c1, nizkCKS.tmpQP.Q)
ct1 = nizkCKS.tmpQP.Q
}
ringQ.MulCoeffsMontgomeryConstantLvl(levelQ, ct1, nizkCKS.tmpDelta, shareOut.Value)
if ringP != nil {
ringQ.MulScalarBigintLvl(levelQ, shareOut.Value, ringP.ModulusAtLevel[levelP], shareOut.Value)
}
if !ct.IsNTT {
ringQ.InvNTTLazyLvl(levelQ, shareOut.Value, shareOut.Value)
nizkCKS.gaussianSampler.ReadLvl(levelQ, nizkCKS.tmpQP.Q)
nizkCKS.e = nizkCKS.tmpQP.Q.CopyNew()
if ringP != nil {
ringQP.ExtendBasisSmallNormAndCenter(nizkCKS.tmpQP.Q, levelP, nil, nizkCKS.tmpQP.P)
}
ringQ.AddLvl(levelQ, shareOut.Value, nizkCKS.tmpQP.Q, shareOut.Value)
if ringP != nil {
nizkCKS.basisExtender.ModDownQPtoQ(levelQ, levelP, shareOut.Value, nizkCKS.tmpQP.P, shareOut.Value)
}
} else {
nizkCKS.gaussianSampler.ReadLvl(levelQ, nizkCKS.tmpQP.Q)
nizkCKS.e = nizkCKS.tmpQP.Q.CopyNew()
if ringP != nil {
ringQP.ExtendBasisSmallNormAndCenter(nizkCKS.tmpQP.Q, levelP, nil, nizkCKS.tmpQP.P)
}
ringQ.InvNTTLvl(levelQ, shareOut.Value, shareOut.Value)
ringQ.AddLvl(levelQ, shareOut.Value, nizkCKS.tmpQP.Q, shareOut.Value)
if ringP != nil {
nizkCKS.basisExtender.ModDownQPtoQ(levelQ, levelP, shareOut.Value, nizkCKS.tmpQP.P, shareOut.Value)
}
ringQ.NTTLvl(levelQ, shareOut.Value, shareOut.Value)
}
shareOut.Value.Resize(levelQ)
}
func (nizkCKS *NizkCKSProtocol) AggregateShares(share1, share2, shareOut *CKSShare) {
nizkCKS.params.RingQ().AddLvl(share1.Value.Level(), share1.Value, share2.Value, shareOut.Value)
}
func (nizkCKS *NizkCKSProtocol) KeySwitch(ctIn *rlwe.Ciphertext, combined *CKSShare, ctOut *rlwe.Ciphertext) {
level := ctIn.Level()
if ctIn != ctOut {
ctOut.Resize(ctIn.Degree(), level)
ring.CopyLvl(level, ctIn.Value[1], ctOut.Value[1])
ctOut.MetaData = ctIn.MetaData
}
nizkCKS.params.RingQ().AddLvl(level, ctIn.Value[0], combined.Value, ctOut.Value[0])
}
func (nizkCKS *NizkCKSProtocol) MarshalNizkParams() []byte {
eBytes, _ := nizkCKS.e.MarshalBinary()
return eBytes
}
func (nizkCKS *NizkCKSProtocol) GetNizkParams() *ring.Poly {
return nizkCKS.e.CopyNew()
}