107 lines
2.7 KiB
Java
107 lines
2.7 KiB
Java
package ShamirSecretSharing;
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import Communication.Network;
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import Communication.User;
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import meerkat.protobuf.DKGMessages;
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import java.math.BigInteger;
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import java.util.Random;
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/**
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* Created by Tzlil on 1/27/2016.
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* an implementation of Shamire's secret sharing scheme
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*/
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public class SecretSharing{
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protected final int t;
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protected final int n;
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protected final BigInteger q;
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protected final Polynomial polynomial;
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/**
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* constructor
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* @param q a large prime.
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* @param t threshold. Any t+1 share holders can recover the secret,
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* but any set of at most t share holders cannot
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* @param n number of share holders
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* @param x secret, chosen from Zq
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* @param random use for generate random polynomial
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*/
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public SecretSharing(int t, int n, BigInteger x, Random random, BigInteger q) {
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this.q = q;
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this.t = t;
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this.n = n;
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this.polynomial = generateRandomPolynomial(x,random);
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}
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/**
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* @param x
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* @param random
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* @return new Polynomial polynomial of degree t ,such that
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* 1. polynomial(0) = x
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* 2. polynomial coefficients randomly chosen from Zq (except of coefficients[0] = x)
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*/
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private Polynomial generateRandomPolynomial(BigInteger x, Random random) {
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BigInteger[] coefficients = new BigInteger[t + 1];
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coefficients[0] = x.mod(q);
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int bits = q.bitLength();
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for (int i = 1 ; i <= t; i++ ){
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coefficients[i] = new BigInteger(bits,random).mod(q);
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}
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return new Polynomial(coefficients);
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}
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/**
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* @param i in range of [1,...n]
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*
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* @return polynomial.image(i)%q
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*/
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public Polynomial.Point getShare(int i){
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assert (i > 0 && i <= n);
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return new Polynomial.Point(BigInteger.valueOf(i), polynomial, q);
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}
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/**
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* @param shares - subset of the original shares
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*
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* @return image of interpolation(shares) at x = 0
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*/
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public static BigInteger restoreSecrete(Polynomial.Point[] shares) throws Exception {
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Polynomial polynomial = Polynomial.interpolation(shares);
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return polynomial.image(BigInteger.ZERO);
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}
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/**
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* getter
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* @return threshold
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*/
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public int getT() {
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return t;
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}
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/**
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* getter
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* @return number of share holders
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*/
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public int getN() {
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return n;
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}
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/**
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* getter
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* @return the prime was given in the constructor
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*/
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public BigInteger getQ() {
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return q;
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}
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/**
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* getter
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* @return the polynomial was generated in constructor
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*/
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public Polynomial getPolynomial() {
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return polynomial;
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}
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}
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