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-rw-r--r--crypto/bn256/google/example_test.go43
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+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package bn256
+
+import (
+ "crypto/rand"
+)
+
+func ExamplePair() {
+ // This implements the tripartite Diffie-Hellman algorithm from "A One
+ // Round Protocol for Tripartite Diffie-Hellman", A. Joux.
+ // http://www.springerlink.com/content/cddc57yyva0hburb/fulltext.pdf
+
+ // Each of three parties, a, b and c, generate a private value.
+ a, _ := rand.Int(rand.Reader, Order)
+ b, _ := rand.Int(rand.Reader, Order)
+ c, _ := rand.Int(rand.Reader, Order)
+
+ // Then each party calculates g₁ and g₂ times their private value.
+ pa := new(G1).ScalarBaseMult(a)
+ qa := new(G2).ScalarBaseMult(a)
+
+ pb := new(G1).ScalarBaseMult(b)
+ qb := new(G2).ScalarBaseMult(b)
+
+ pc := new(G1).ScalarBaseMult(c)
+ qc := new(G2).ScalarBaseMult(c)
+
+ // Now each party exchanges its public values with the other two and
+ // all parties can calculate the shared key.
+ k1 := Pair(pb, qc)
+ k1.ScalarMult(k1, a)
+
+ k2 := Pair(pc, qa)
+ k2.ScalarMult(k2, b)
+
+ k3 := Pair(pa, qb)
+ k3.ScalarMult(k3, c)
+
+ // k1, k2 and k3 will all be equal.
+}