mirror of https://github.com/cheat/cheat.git
63 lines
1.4 KiB
Go
63 lines
1.4 KiB
Go
package goldilocks
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import (
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"crypto/subtle"
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mlsb "github.com/cloudflare/circl/math/mlsbset"
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)
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const (
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// MLSBRecoding parameters
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fxT = 448
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fxV = 2
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fxW = 3
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fx2w1 = 1 << (uint(fxW) - 1)
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)
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// ScalarBaseMult returns kG where G is the generator point.
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func (e twistCurve) ScalarBaseMult(k *Scalar) *twistPoint {
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m, err := mlsb.New(fxT, fxV, fxW)
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if err != nil {
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panic(err)
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}
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if m.IsExtended() {
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panic("not extended")
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}
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var isZero int
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if k.IsZero() {
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isZero = 1
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}
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subtle.ConstantTimeCopy(isZero, k[:], order[:])
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minusK := *k
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isEven := 1 - int(k[0]&0x1)
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minusK.Neg()
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subtle.ConstantTimeCopy(isEven, k[:], minusK[:])
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c, err := m.Encode(k[:])
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if err != nil {
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panic(err)
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}
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gP := c.Exp(groupMLSB{})
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P := gP.(*twistPoint)
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P.cneg(uint(isEven))
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return P
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}
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type groupMLSB struct{}
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func (e groupMLSB) ExtendedEltP() mlsb.EltP { return nil }
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func (e groupMLSB) Sqr(x mlsb.EltG) { x.(*twistPoint).Double() }
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func (e groupMLSB) Mul(x mlsb.EltG, y mlsb.EltP) { x.(*twistPoint).mixAddZ1(y.(*preTwistPointAffine)) }
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func (e groupMLSB) Identity() mlsb.EltG { return twistCurve{}.Identity() }
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func (e groupMLSB) NewEltP() mlsb.EltP { return &preTwistPointAffine{} }
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func (e groupMLSB) Lookup(a mlsb.EltP, v uint, s, u int32) {
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Tabj := &tabFixMult[v]
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P := a.(*preTwistPointAffine)
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for k := range Tabj {
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P.cmov(&Tabj[k], uint(subtle.ConstantTimeEq(int32(k), u)))
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}
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P.cneg(int(s >> 31))
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}
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