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avoid race condition in MakeAffine/ValidatePairing #59

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May 10, 2024
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avoid race condition in MakeAffine/ValidatePairing #59

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9 changes: 6 additions & 3 deletions pairing/bn254/suite.go
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Original file line number Diff line number Diff line change
Expand Up @@ -132,10 +132,13 @@ func (s *Suite) Pair(p1 kyber.Point, p2 kyber.Point) kyber.Point {
return s.GT().Point().(*pointGT).Pair(p1, p2)
}

// NB: Not safe for concurrent calls
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I'm not 100% sure this is actually true since now you clone the inputs 🤔

func (s *Suite) ValidatePairing(p1, p2, inv1, inv2 kyber.Point) bool {
p2.(*pointG2).g.MakeAffine()
inv2.(*pointG2).g.MakeAffine()
return s.Pair(p1, p2).Equal(s.Pair(inv1, inv2))
p2Norm := p2.Clone()
inv2Norm := inv2.Clone()
p2Norm.(*pointG2).g.MakeAffine()
inv2Norm.(*pointG2).g.MakeAffine()
return s.Pair(p1, p2Norm).Equal(s.Pair(inv1, inv2Norm))
}

// Not used other than for reflect.TypeOf()
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27 changes: 15 additions & 12 deletions pairing/bn254/twist.go
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Original file line number Diff line number Diff line change
Expand Up @@ -177,24 +177,27 @@ func (c *twistPoint) Mul(a *twistPoint, scalar *big.Int) {
c.Set(sum)
}

// NB: Not safe for concurrent calls
func (c *twistPoint) MakeAffine() {
if c.z.IsOne() {
g := c.Clone()
if g.z.IsOne() {
return
} else if c.z.IsZero() {
c.x.SetZero()
c.y.SetOne()
c.t.SetZero()
} else if g.z.IsZero() {
g.x.SetZero()
g.y.SetOne()
g.t.SetZero()
return
}

zInv := (&gfP2{}).Invert(&c.z)
t := (&gfP2{}).Mul(&c.y, zInv)
zInv := (&gfP2{}).Invert(&g.z)
t := (&gfP2{}).Mul(&g.y, zInv)
zInv2 := (&gfP2{}).Square(zInv)
c.y.Mul(t, zInv2)
t.Mul(&c.x, zInv2)
c.x.Set(t)
c.z.SetOne()
c.t.SetOne()
g.y.Mul(t, zInv2)
t.Mul(&g.x, zInv2)
g.x.Set(t)
g.z.SetOne()
g.t.SetOne()
c.Set(g)
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Because of this Set here, I don't think using a Cloned g actually changes much, except it makes the timing of a race more difficult to "hit" in prod/tests...
This function should definitively have a "not safe for concurrent use" in the comment.

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Yeah this bit is dicey. I added the "not safe for concurrent use" warning above the function.

}

func (c *twistPoint) Neg(a *twistPoint) {
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