From bd6879ac518431174a490ba42f7e6e822dcb3ee1 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?P=C3=A9ter=20Szil=C3=A1gyi?= <peterke@gmail.com>
Date: Mon, 5 Mar 2018 14:33:45 +0200
Subject: core/vm, crypto/bn256: switch over to cloudflare library (#16203)

* core/vm, crypto/bn256: switch over to cloudflare library

* crypto/bn256: unmarshal constraint + start pure go impl

* crypto/bn256: combo cloudflare and google lib

* travis: drop 386 test job
---
 crypto/bn256/cloudflare/gfp12.go | 160 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 160 insertions(+)
 create mode 100644 crypto/bn256/cloudflare/gfp12.go

(limited to 'crypto/bn256/cloudflare/gfp12.go')

diff --git a/crypto/bn256/cloudflare/gfp12.go b/crypto/bn256/cloudflare/gfp12.go
new file mode 100644
index 000000000..93fb368a7
--- /dev/null
+++ b/crypto/bn256/cloudflare/gfp12.go
@@ -0,0 +1,160 @@
+package bn256
+
+// For details of the algorithms used, see "Multiplication and Squaring on
+// Pairing-Friendly Fields, Devegili et al.
+// http://eprint.iacr.org/2006/471.pdf.
+
+import (
+	"math/big"
+)
+
+// gfP12 implements the field of size p¹² as a quadratic extension of gfP6
+// where ω²=τ.
+type gfP12 struct {
+	x, y gfP6 // value is xω + y
+}
+
+func (e *gfP12) String() string {
+	return "(" + e.x.String() + "," + e.y.String() + ")"
+}
+
+func (e *gfP12) Set(a *gfP12) *gfP12 {
+	e.x.Set(&a.x)
+	e.y.Set(&a.y)
+	return e
+}
+
+func (e *gfP12) SetZero() *gfP12 {
+	e.x.SetZero()
+	e.y.SetZero()
+	return e
+}
+
+func (e *gfP12) SetOne() *gfP12 {
+	e.x.SetZero()
+	e.y.SetOne()
+	return e
+}
+
+func (e *gfP12) IsZero() bool {
+	return e.x.IsZero() && e.y.IsZero()
+}
+
+func (e *gfP12) IsOne() bool {
+	return e.x.IsZero() && e.y.IsOne()
+}
+
+func (e *gfP12) Conjugate(a *gfP12) *gfP12 {
+	e.x.Neg(&a.x)
+	e.y.Set(&a.y)
+	return e
+}
+
+func (e *gfP12) Neg(a *gfP12) *gfP12 {
+	e.x.Neg(&a.x)
+	e.y.Neg(&a.y)
+	return e
+}
+
+// Frobenius computes (xω+y)^p = x^p ω·ξ^((p-1)/6) + y^p
+func (e *gfP12) Frobenius(a *gfP12) *gfP12 {
+	e.x.Frobenius(&a.x)
+	e.y.Frobenius(&a.y)
+	e.x.MulScalar(&e.x, xiToPMinus1Over6)
+	return e
+}
+
+// FrobeniusP2 computes (xω+y)^p² = x^p² ω·ξ^((p²-1)/6) + y^p²
+func (e *gfP12) FrobeniusP2(a *gfP12) *gfP12 {
+	e.x.FrobeniusP2(&a.x)
+	e.x.MulGFP(&e.x, xiToPSquaredMinus1Over6)
+	e.y.FrobeniusP2(&a.y)
+	return e
+}
+
+func (e *gfP12) FrobeniusP4(a *gfP12) *gfP12 {
+	e.x.FrobeniusP4(&a.x)
+	e.x.MulGFP(&e.x, xiToPSquaredMinus1Over3)
+	e.y.FrobeniusP4(&a.y)
+	return e
+}
+
+func (e *gfP12) Add(a, b *gfP12) *gfP12 {
+	e.x.Add(&a.x, &b.x)
+	e.y.Add(&a.y, &b.y)
+	return e
+}
+
+func (e *gfP12) Sub(a, b *gfP12) *gfP12 {
+	e.x.Sub(&a.x, &b.x)
+	e.y.Sub(&a.y, &b.y)
+	return e
+}
+
+func (e *gfP12) Mul(a, b *gfP12) *gfP12 {
+	tx := (&gfP6{}).Mul(&a.x, &b.y)
+	t := (&gfP6{}).Mul(&b.x, &a.y)
+	tx.Add(tx, t)
+
+	ty := (&gfP6{}).Mul(&a.y, &b.y)
+	t.Mul(&a.x, &b.x).MulTau(t)
+
+	e.x.Set(tx)
+	e.y.Add(ty, t)
+	return e
+}
+
+func (e *gfP12) MulScalar(a *gfP12, b *gfP6) *gfP12 {
+	e.x.Mul(&e.x, b)
+	e.y.Mul(&e.y, b)
+	return e
+}
+
+func (c *gfP12) Exp(a *gfP12, power *big.Int) *gfP12 {
+	sum := (&gfP12{}).SetOne()
+	t := &gfP12{}
+
+	for i := power.BitLen() - 1; i >= 0; i-- {
+		t.Square(sum)
+		if power.Bit(i) != 0 {
+			sum.Mul(t, a)
+		} else {
+			sum.Set(t)
+		}
+	}
+
+	c.Set(sum)
+	return c
+}
+
+func (e *gfP12) Square(a *gfP12) *gfP12 {
+	// Complex squaring algorithm
+	v0 := (&gfP6{}).Mul(&a.x, &a.y)
+
+	t := (&gfP6{}).MulTau(&a.x)
+	t.Add(&a.y, t)
+	ty := (&gfP6{}).Add(&a.x, &a.y)
+	ty.Mul(ty, t).Sub(ty, v0)
+	t.MulTau(v0)
+	ty.Sub(ty, t)
+
+	e.x.Add(v0, v0)
+	e.y.Set(ty)
+	return e
+}
+
+func (e *gfP12) Invert(a *gfP12) *gfP12 {
+	// See "Implementing cryptographic pairings", M. Scott, section 3.2.
+	// ftp://136.206.11.249/pub/crypto/pairings.pdf
+	t1, t2 := &gfP6{}, &gfP6{}
+
+	t1.Square(&a.x)
+	t2.Square(&a.y)
+	t1.MulTau(t1).Sub(t2, t1)
+	t2.Invert(t1)
+
+	e.x.Neg(&a.x)
+	e.y.Set(&a.y)
+	e.MulScalar(e, t2)
+	return e
+}
-- 
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