mcl/ffi/java/java.md

JNI for mcl (experimental)

This library provides functionality to compute the optimal ate pairing over Barreto-Naehrig (BN) or BLS12-381 curves.

Initialization

Load the library mcljava.

import com.herumi.mcl.*;

System.loadLibrary(System.mapLibraryName("mcljava"));
Mcl.SystemInit(curveType); // curveType = Mcl.BN254 or Mcl.BLS12_381

Classes

• G1 ; The cyclic group instantiated as E(Fp)[r] where where r = p + 1 - t.
• G2 ; The cyclic group instantiated as the inverse image of E'(Fp^2)[r].
• GT ; The cyclic group in the image of the optimal ate pairing.
  • e : G1 x G2 -> GT
• Fr ; The finite field with characteristic r.

Methods and Functions

Fr

• Fr::setInt(int x) ; set by x
• Fr::setStr(String str) ; set by str such as "123", "0xfff", etc.
• Fr::setByCSPRNG() ; randomly set
• Mcl.neg(Fr y, Fr x) ; y = -x
• Mcl.add(Fr z, Fr x, Fr y) ; z = x + y
• Mcl.sub(Fr z, Fr x, Fr y) ; z = x - y
• Mcl.mul(Fr z, Fr x, Fr y) ; z = x * y
• Mcl.div(Fr z, Fr x, Fr y) ; z = x / y

G1

• Mcl.neg(G1 y, G1 x) ; y = -x
• Mcl.dbl(G1 y, G1 x) ; y = 2x
• Mcl.add(G1 z, G1 x, G1 y) ; z = x + y
• Mcl.sub(G1 z, G1 x, G1 y) ; z = x - y
• Mcl.mul(G1 z, G1 x, Fr y) ; z = x * y

G2

• Mcl.neg(G2 y, G2 x) ; y = -x
• Mcl.dbl(G2 y, G2 x) ; y = 2x
• Mcl.add(G2 z, G2 x, G2 y) ; z = x + y
• Mcl.sub(G2 z, G2 x, G2 y) ; z = x - y
• Mcl.mul(G2 z, G2 x, Fr y) ; z = x * y

GT

• GT::setStr(String str) ; set by the result of toString() method
• Mcl.mul(GT z, GT x, GT y) ; z = x * y
• Mcl.pow(GT z, GT x, Fr y) ; z = x ^ y

pairing

• Mcl.pairing(GT e, G1 P, G2 Q) ; e = e(P, Q)

BLS signature sample

G2 Q = new G2();
Mcl.hashAndMapToG2(Q, "abc".getBytes());

Fr s = new Fr();
s.setByCSPRNG(); // secret key
G2 pub = new G2();
Mcl.mul(pub, Q, s); // public key = sQ

String m = "signature test";
G1 H = new G1();
Mcl.hashAndMapToG1(H, m.getBytes()); // H = Hash(m)
G1 sign = new G1();
Mcl.mul(sign, H, s); // signature of m = s H

GT e1 = new GT();
GT e2 = new GT();
Mcl.pairing(e1, H, pub); // e1 = e(H, s Q)
Mcl.pairing(e2, sign, Q); // e2 = e(s H, Q);
assertBool("verify signature", e1.equals(e2));

Make test

cd ffi/java
make test

Sample code

MclTest.java