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package nizk
import (
. "kesim.org/seal/common"
"kesim.org/seal/nizk/schnorr"
)
type Bit struct {
id Bytes
set bool
α *Scalar
β *Scalar
*Commitment
Proof *Proof
*Stage
}
type Commitment struct {
A *Point // g^α
B *Point // g^β
C *Point // g^(ab)g^(set)
}
// This is a construction of a proof of a statement of the form
//
// [(C = g^(αβ)) && (A = g^α) && (Β = g^β)]
// || [(C = g^(αβ+1)) && (A = g^α) && (Β = g^β)]
//
// for given C, A and B
type Proof struct {
A *schnorr.Proof // Proof for knowledge of α in A = G^α
B *schnorr.Proof // Proof for knowledge of β in B = G^β
C struct { // Proof for knowledge of statement above
Ch [2]*Scalar
R [2]*Scalar
}
}
func NewBit(id Bytes, set bool) *Bit {
α, β := Curve.RandomScalar(), Curve.RandomScalar()
return NewBitFromScalars(id, set, α, β)
}
func NewBitFromScalars(id Bytes, set bool, α, β *Scalar) *Bit {
b := &Bit{
id: id,
set: set,
α: α,
β: β,
}
b.commit()
b.proof()
return b
}
func (b *Bit) IsSet() bool {
return b.set
}
func (b *Bit) commit() {
if b.Commitment != nil {
return
}
var C *Point
c := b.α.Mul(b.β)
if b.set {
C = G.Exp(c.Add(One))
} else {
C = G.Exp(c)
}
b.Commitment = &Commitment{
C: C,
A: G.Exp(b.α),
B: G.Exp(b.β),
}
}
func (s *Bit) proof() {
if s.Proof != nil {
return
}
var e [2][2]*Point
var r1, r2, w *Scalar
r1 = Curve.RandomScalar()
r2 = Curve.RandomScalar()
w = Curve.RandomScalar()
s.commit()
c := s.Commitment
if s.set {
e[0][0] = G.Exp(r1)
e[0][1] = c.B.Exp(r1).Mul(G.Exp(w))
e[1][0] = G.Exp(r2)
e[1][1] = c.B.Exp(r2)
} else {
e[0][0] = G.Exp(r1)
e[0][1] = c.B.Exp(r1)
e[1][0] = G.Exp(r2).Mul(c.A.Exp(w))
e[1][1] = c.B.Exp(r2).Mul(c.C.Div(G).Exp(w))
}
ch := Challenge(G, c.C, c.A, c.B, e[0][0], e[0][1], e[1][0], e[1][1], s.id)
pr := &Proof{}
if s.set {
pr.C.Ch[0] = w
pr.C.Ch[1] = ch.Sub(w)
pr.C.R[0] = r1.Sub(s.α.Mul(pr.C.Ch[0]))
pr.C.R[1] = r2.Sub(s.α.Mul(pr.C.Ch[1]))
} else {
pr.C.Ch[0] = ch.Sub(w)
pr.C.Ch[1] = w
pr.C.R[0] = r1.Sub(s.α.Mul(pr.C.Ch[0]))
pr.C.R[1] = r2
}
pr.A = (*schnorr.Statement)(s.α).Proof(s.id)
pr.B = (*schnorr.Statement)(s.β).Proof(s.id)
s.Proof = pr
}
func (c *Commitment) Verify(id Bytes, p *Proof) bool {
var e [2][2]*Point
e[0][0] = G.Exp(p.C.R[0]).Mul(c.A.Exp(p.C.Ch[0]))
e[0][1] = c.B.Exp(p.C.R[0]).Mul(c.C.Exp(p.C.Ch[0]))
e[1][0] = G.Exp(p.C.R[1]).Mul(c.A.Exp(p.C.Ch[1]))
e[1][1] = c.B.Exp(p.C.R[1]).Mul(c.C.Div(G).Exp(p.C.Ch[1]))
ch := Challenge(G, c.C, c.A, c.B, e[0][0], e[0][1], e[1][0], e[1][1], id)
return p.C.Ch[0].Add(p.C.Ch[1]).Equal(ch) &&
(*schnorr.Commitment)(c.A).Verify(p.A, id) &&
(*schnorr.Commitment)(c.B).Verify(p.B, id)
}
|
