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