62 lines
1.6 KiB
Go
62 lines
1.6 KiB
Go
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// Copyright 2023 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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//go:build !purego && (amd64 || arm64 || ppc64le || s390x)
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package nistec
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import "sources.truenas.cloud/code/nistec/internal/fiat"
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// Negate sets p = -q and returns p.
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func (p *P256Point) Negate(q *P256Point) *P256Point {
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// fiat.P256Element is a little-endian Montgomery domain fully-reduced
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// element, like p256Element, so they are actually interchangable.
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qy := new(fiat.P256Element)
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*qy.Bits() = q.y
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py := new(fiat.P256Element).Sub(new(fiat.P256Element), qy)
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p.x = q.x
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p.y = *py.Bits()
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p.z = q.z
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return p
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}
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// IsInfinity returns 1 if p is the point-at-infinity, 0 otherwise.
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func (p *P256Point) IsInfinity() int {
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return p.isInfinity()
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}
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// Equal returns 1 if p and q represent the same point, 0 otherwise.
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func (p *P256Point) Equal(q *P256Point) int {
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pinf := p256Equal(&p.z, &p256Zero)
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qinf := p256Equal(&q.z, &p256Zero)
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bothinf := pinf & qinf
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noneinf := (1 - pinf) & (1 - qinf)
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// xp = Xp / Zp²
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// yp = Yp / Zp³
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// xq = Xq / Zq²
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// yq = Yq / Zq³
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// If Zp != 0 and Zq != 0, then:
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// xp == yp <=> Xp*Zq² == Xq*Zp²
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// xq == yq <=> Yp*Zq³ == Yq*Zp³
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px := new(p256Element)
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qx := new(p256Element)
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py := new(p256Element)
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qy := new(p256Element)
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pz := new(p256Element)
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qz := new(p256Element)
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p256Sqr(pz, &p.z, 1)
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p256Sqr(qz, &q.z, 1)
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p256Mul(px, &p.x, qz)
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p256Mul(qx, &q.x, pz)
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samex := p256Equal(px, qx)
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p256Mul(pz, pz, &p.z)
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p256Mul(qz, qz, &q.z)
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p256Mul(py, &p.y, qz)
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p256Mul(qy, &q.y, pz)
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samey := p256Equal(py, qy)
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return bothinf | (noneinf & samex & samey)
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}
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