bouncycastle(7)Learn from others DSA

bouncycastle(7)Learn from others DSA

DSA (Digital Signature Algorithm)

A will generate the key pair, share the public key to B.
A will use private key to generate the signature, send the signature and data to B.
B will use public key to validate the signature and data.

package com.sillycat.easycastle.encryption;

import java.security.Key;
import java.security.KeyFactory;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.SecureRandom;
import java.security.Signature;
import java.security.interfaces.DSAPrivateKey;
import java.security.interfaces.DSAPublicKey;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;
import java.util.HashMap;
import java.util.Map;

public abstract class DSACoder extends Coder {

     public static final String ALGORITHM = "DSA";
     
    /**
     * default key size
     * <pre>
     * DSA
     * Default Keysize 1024 
     * Keysize must be a multiple of 64, ranging from 512 to 1024 (inclusive).
     * </pre>
     */
    private static final int KEY_SIZE = 1024;

    /**
     * default seed
     */
    private static final String DEFAULT_SEED = "0f22507a10bbddd07d8a3082122966e3";

    private static final String PUBLIC_KEY = "DSAPublicKey";
    private static final String PRIVATE_KEY = "DSAPrivateKey";

    /**
     * use private key to signature the data
     * @param data
     * @param privateKey
     *
     * @return
     * @throws Exception
     */
    public static String sign(byte[] data, String privateKey) throws Exception {
         // decrypt the private key
        byte[] keyBytes = decryptBASE64(privateKey);
        PKCS8EncodedKeySpec pkcs8KeySpec = new PKCS8EncodedKeySpec(keyBytes);
        // KEY_ALGORITHM
        KeyFactory keyFactory = KeyFactory.getInstance(ALGORITHM);
        // convert to private key object
        PrivateKey priKey = keyFactory.generatePrivate(pkcs8KeySpec);
        // signature the data
        Signature signature = Signature.getInstance(keyFactory.getAlgorithm());
        signature.initSign(priKey);
        signature.update(data);
        return encryptBASE64(signature.sign());
    }

    /**
     * validate the signature
     * @param data
     * @param publicKey
     * @param sign
     * @return true false
     * @throws Exception
     */
    public static boolean verify(byte[] data, String publicKey, String sign)
            throws Exception {
        byte[] keyBytes = decryptBASE64(publicKey);
        X509EncodedKeySpec keySpec = new X509EncodedKeySpec(keyBytes);
        // ALGORITHM
        KeyFactory keyFactory = KeyFactory.getInstance(ALGORITHM);
        // convert to public key object
        PublicKey pubKey = keyFactory.generatePublic(keySpec);

        Signature signature = Signature.getInstance(keyFactory.getAlgorithm());
        signature.initVerify(pubKey);
        signature.update(data);
        return signature.verify(decryptBASE64(sign));
    }
    /**
     * generate the key pair
     * @param seed
     * @return
     * @throws Exception
     */
    public static Map<String, Object> initKey(String seed) throws Exception {
        KeyPairGenerator keygen = KeyPairGenerator.getInstance(ALGORITHM);
        SecureRandom secureRandom = new SecureRandom();
        secureRandom.setSeed(seed.getBytes());
        keygen.initialize(KEY_SIZE, secureRandom);
        KeyPair keys = keygen.genKeyPair();
        DSAPublicKey publicKey = (DSAPublicKey) keys.getPublic();
        DSAPrivateKey privateKey = (DSAPrivateKey) keys.getPrivate();
        Map<String, Object> map = new HashMap<String, Object>(2);
        map.put(PUBLIC_KEY, publicKey);
        map.put(PRIVATE_KEY, privateKey);
        return map;
    }
    /**
     * return key map object
     * @return
     * @throws Exception
     */
    public static Map<String, Object> initKey() throws Exception {
        return initKey(DEFAULT_SEED);
    }
    /**
     * return private key
     * @param keyMap
     * @return
     * @throws Exception
     */
    public static String getPrivateKey(Map<String, Object> keyMap)
            throws Exception {
        Key key = (Key) keyMap.get(PRIVATE_KEY);
        return encryptBASE64(key.getEncoded());
    }
    /**
     * return public key
     * @param keyMap
     * @return
     * @throws Exception
     */
    public static String getPublicKey(Map<String, Object> keyMap)
            throws Exception {
        Key key = (Key) keyMap.get(PUBLIC_KEY);
        return encryptBASE64(key.getEncoded());
    }
}


The test case will be as follow:
package com.sillycat.easycastle.encryption;

importstatic org.junit.Assert.assertTrue;

import java.util.Map;

import org.junit.Test;

publicclass DSACoderTest {

@Test
publicvoid test() throws Exception {
String inputStr = "hello world";
byte[] data = inputStr.getBytes();

// init the key pair
Map<String, Object> keyMap = DSACoder.initKey();

// get the public and private key
String publicKey = DSACoder.getPublicKey(keyMap);
String privateKey = DSACoder.getPrivateKey(keyMap);

System.out.println("public key:\r" + publicKey);
System.out.println("private key:\r" + privateKey);

// generate the signature
String sign = DSACoder.sign(data, privateKey);
System.out.println("signature:\r" + sign);

// validate the signature
boolean status = DSACoder.verify(data, publicKey, sign);
System.out.println("status:\r" + status);
assertTrue(status);
}

}


references:
http://snowolf.iteye.com/blog/382749