Returns whether the Diffie-Hellman public key is valid or not. - Java Security

Java examples for Security:Key

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Description

Returns whether the Diffie-Hellman public key is valid or not.

Demo Code

/*//  ww  w.j  av a  2  s.c om
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 * by Oracle in the LICENSE file that accompanied this code.
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 * This code is distributed in the hope that it will be useful, but WITHOUT
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 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
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//package com.java2s;

import java.security.InvalidKeyException;

import javax.crypto.interfaces.DHPublicKey;
import javax.crypto.spec.DHParameterSpec;
import javax.crypto.spec.DHPublicKeySpec;
import java.math.BigInteger;

public class Main {
    /**
     * Returns whether the Diffie-Hellman public key is valid or not.
     *
     * Per RFC 2631 and NIST SP800-56A, the following algorithm is used to
     * validate Diffie-Hellman public keys:
     * 1. Verify that y lies within the interval [2,p-1]. If it does not,
     *    the key is invalid.
     * 2. Compute y^q mod p. If the result == 1, the key is valid.
     *    Otherwise the key is invalid.
     */
    private static void validateDHPublicKey(DHPublicKey publicKey)
            throws InvalidKeyException {
        DHParameterSpec paramSpec = publicKey.getParams();

        BigInteger p = paramSpec.getP();
        BigInteger g = paramSpec.getG();
        BigInteger y = publicKey.getY();

        validateDHPublicKey(p, g, y);
    }

    private static void validateDHPublicKey(DHPublicKeySpec publicKeySpec)
            throws InvalidKeyException {
        validateDHPublicKey(publicKeySpec.getP(), publicKeySpec.getG(),
                publicKeySpec.getY());
    }

    private static void validateDHPublicKey(BigInteger p, BigInteger g,
            BigInteger y) throws InvalidKeyException {

        // For better interoperability, the interval is limited to [2, p-2].
        BigInteger leftOpen = BigInteger.ONE;
        BigInteger rightOpen = p.subtract(BigInteger.ONE);
        if (y.compareTo(leftOpen) <= 0) {
            throw new InvalidKeyException(
                    "Diffie-Hellman public key is too small");
        }
        if (y.compareTo(rightOpen) >= 0) {
            throw new InvalidKeyException(
                    "Diffie-Hellman public key is too large");
        }

        // Don't bother to check against the y^q mod p if safe primes are used.
    }
}

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