常用数字签名算法RSA与DSA的Java程序内实现示例

RSA加密算法
我们来回顾一下RSA的加密算法。我们从公钥加密算法和签名算法的定义出发，用比较规范的语言来描述这一算法。
RSA公钥加密体制包含如下3个算法：KeyGen（密钥生成算法），Encrypt（加密算法）以及Decrypt（解密算法）。
密钥生成算法以安全常数作为输入，输出一个公钥PK，和一个私钥SK。安全常数用于确定这个加密算法的安全性有多高，一般以加密算法使用的质数p的大小有关。越大，质数p一般越大，保证体制有更高的安全性。在RSA中，密钥生成算法如下：算法首先随机产生两个不同大质数p和q，计算N=pq。随后，算法计算欧拉函数。接下来，算法随机选择一个小于的整数e，并计算e关于的模反元素d。最后，公钥为PK=(N, e)，私钥为SK=（N, d）。
加密算法以公钥PK和待加密的消息M作为输入，输出密文CT。在RSA中，加密算法如下：算法直接输出密文为
解密算法以私钥SK和密文CT作为输入，输出消息M。在RSA中，解密算法如下：算法直接输出明文为。由于e和d在下互逆，因此我们有：
所以，从算法描述中我们也可以看出：公钥用于对数据进行加密，私钥用于对数据进行解密。当然了，这个也可以很直观的理解：公钥就是公开的密钥，其公开了大家才能用它来加密数据。私钥是私有的密钥，谁有这个密钥才能够解密密文。否则大家都能看到私钥，就都能解密，那不就乱套了。
下面就来看一下Java中的简单实现：

package com.stone.security; 
 
import java.security.KeyPair; 
import java.security.KeyPairGenerator; 
import java.security.PrivateKey; 
import java.security.PublicKey; 
import java.util.Arrays; 
 
import javax.crypto.Cipher; 
 
 
public class RSA { 
 public static final String KEY_ALGORITHM = "RSA"; 
 public static final String CIPHER_ALGORITHM_ECB1 = "RSA/ECB/PKCS1Padding"; 
 public static final String CIPHER_ALGORITHM_ECB2 = "RSA/ECB/OAEPWithSHA-1AndMGF1Padding"; //不能用 
 public static final String CIPHER_ALGORITHM_ECB3 = "OAEPWithSHA-256AndMGF1Padding"; //不能用 
 
 static PublicKey publicKey; 
 static PrivateKey privateKey; 
 static Cipher cipher; 
 static KeyPair keyPair; 
 
 public static void main(String[] args) throws Exception { 
 method1("斯柯达U*(Sfsad7f()*^%%$"); 
 method2("斯柯达U*(Sfsad7f()*^%%$"); 
 method3("斯柯达U*(Sfsad7f()*^%%$"); 
  
 } 
 
  
 static void method1(String str) throws Exception { 
 KeyPairGenerator keyGenerator = KeyPairGenerator.getInstance(KEY_ALGORITHM); 
 KeyPair keyPair = keyGenerator.generateKeyPair(); 
 publicKey = keyPair.getPublic(); 
 privateKey = keyPair.getPrivate(); 
 cipher = Cipher.getInstance(KEY_ALGORITHM); 
 cipher.init(Cipher.ENCRYPT_MODE, publicKey); //公钥加密 
 byte[] encrypt = cipher.doFinal(str.getBytes()); 
 System.out.println("公钥加密后1：" + Arrays.toString(encrypt)); 
  
 cipher.init(Cipher.DECRYPT_MODE, privateKey);//私钥解密 
 byte[] decrypt = cipher.doFinal(encrypt); 
 System.out.println("私钥解密后1：" + new String(decrypt)); 
 } 
 
  
 static void method2(String str) throws Exception { 
 KeyPairGenerator keyGenerator = KeyPairGenerator.getInstance(KEY_ALGORITHM); 
 KeyPair keyPair = keyGenerator.generateKeyPair(); 
 publicKey = keyPair.getPublic(); 
 privateKey = keyPair.getPrivate(); 
 cipher = Cipher.getInstance(KEY_ALGORITHM); 
 cipher.init(Cipher.ENCRYPT_MODE, privateKey); //私钥加密 
 byte[] encrypt = cipher.doFinal(str.getBytes()); 
 System.out.println("私钥加密后2：" + Arrays.toString(encrypt)); 
  
 cipher.init(Cipher.DECRYPT_MODE, publicKey);//公钥解密 
 byte[] decrypt = cipher.doFinal(encrypt); 
 System.out.println("公钥解密后2：" + new String(decrypt)); 
 } 
 
  
 static void method3(String str) throws Exception { 
 KeyPairGenerator keyGenerator = KeyPairGenerator.getInstance(KEY_ALGORITHM); 
 KeyPair keyPair = keyGenerator.generateKeyPair(); 
 publicKey = keyPair.getPublic(); 
 privateKey = keyPair.getPrivate(); 
 cipher = Cipher.getInstance(CIPHER_ALGORITHM_ECB1); 
 cipher.init(Cipher.ENCRYPT_MODE, privateKey); //私钥加密 
 byte[] encrypt = cipher.doFinal(str.getBytes()); 
 System.out.println("私钥加密后3：" + Arrays.toString(encrypt)); 
  
 cipher.init(Cipher.DECRYPT_MODE, publicKey);//公钥解密 
 byte[] decrypt = cipher.doFinal(encrypt); 
 System.out.println("公钥解密后3：" + new String(decrypt)); 
 } 
} 

DSA算法和数字签名
DSA 一般用于数字签名和认证。
DSA是Schnorr和ElGamal签名算法的变种，被美国NIST作为DSS(DigitalSignature Standard)。
DSA是基于整数有限域离散对数难题的，其安全性与RSA相比差不多。
在DSA数字签名和认证中，发送者使用自己的私钥对文件或消息进行签名，接受者收到消息后使用发送者的公钥
来验证签名的真实性。DSA只是一种算法，和RSA不同之处在于它不能用作加密和解密，也不能进行密钥交换，
只用于签名,它比RSA要快很多.

package com.stone.security; 
 
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.spec.PKCS8EncodedKeySpec; 
import java.security.spec.X509EncodedKeySpec; 
import java.util.HashMap; 
import java.util.Map; 
 
import sun.misc.base64Decoder; 
import sun.misc.base64Encoder; 
 
 
public class DSA { 
  
 public static final String KEY_ALGORITHM = "RSA"; 
 public static final String SIGNATURE_ALGORITHM = "MD5withRSA";*/ 
 
 public static final String KEY_ALGORITHM = "DSA"; 
 public static final String SIGNATURE_ALGORITHM = "DSA"; 
 
 public static final String DEFAULT_SEED = "$%^*%^()(HJG8awfjas7"; //默认种子 
 public static final String PUBLIC_KEY = "DSAPublicKey"; 
 public static final String PRIVATE_KEY = "DSAPrivateKey"; 
 
 public static void main(String[] args) throws Exception { 
 String str = "!@#$!#^$#&ZXVDF呆军工路爱着你*()_+"; 
 byte[] data = str.getBytes(); 
  
 Map keyMap = initKey();// 构建密钥 
 PublicKey publicKey = (PublicKey) keyMap.get(PUBLIC_KEY); 
 PrivateKey privateKey = (PrivateKey) keyMap.get(PRIVATE_KEY); 
 System.out.println("私钥format：" + privateKey.getFormat()); 
 System.out.println("公钥format：" + publicKey.getFormat()); 
  
  
 // 产生签名 
 String sign = sign(data, getPrivateKey(keyMap)); 
  
 // 验证签名 
 boolean verify1 = verify("aaa".getBytes(), getPublicKey(keyMap), sign); 
 System.err.println("经验证 数据和签名匹配:" + verify1); 
  
 boolean verify = verify(data, getPublicKey(keyMap), sign); 
 System.err.println("经验证 数据和签名匹配:" + verify); 
 } 
 
  
 public static Map initKey(String seed) throws Exception { 
 System.out.println("生成密钥"); 
  
 KeyPairGenerator keygen = KeyPairGenerator.getInstance(KEY_ALGORITHM); 
 SecureRandom secureRandom = new SecureRandom(); 
 secureRandom.setSeed(seed.getBytes()); 
 //Modulus size must range from 512 to 1024 and be a multiple of 64 
 keygen.initialize(640, secureRandom); 
  
 KeyPair keys = keygen.genKeyPair(); 
 PrivateKey privateKey = keys.getPrivate(); 
 PublicKey publicKey = keys.getPublic(); 
  
 Map map = new HashMap(2); 
 map.put(PUBLIC_KEY, publicKey); 
 map.put(PRIVATE_KEY, privateKey); 
 return map; 
 } 
 
  
 public static Map initKey() throws Exception { 
 return initKey(DEFAULT_SEED); 
 } 
 
  
 public static String getPrivateKey(Map keyMap) throws Exception { 
 Key key = (Key) keyMap.get(PRIVATE_KEY); 
 return encryptbase64(key.getEncoded()); //base64加密私钥 
 } 
 
  
 public static String getPublicKey(Map keyMap) throws Exception { 
 Key key = (Key) keyMap.get(PUBLIC_KEY); 
 return encryptbase64(key.getEncoded()); //base64加密公钥 
 } 
 
  
 public static String sign(byte[] data, String privateKey) throws Exception { 
 System.out.println("用私钥对信息进行数字签名"); 
  
 byte[] keyBytes = decryptbase64(privateKey); 
 PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(keyBytes); 
 KeyFactory factory = KeyFactory.getInstance(KEY_ALGORITHM); 
 PrivateKey priKey = factory.generatePrivate(keySpec);//生成 私钥 
  
 //用私钥对信息进行数字签名 
 Signature signature = Signature.getInstance(SIGNATURE_ALGORITHM); 
 signature.initSign(priKey); 
 signature.update(data); 
 return encryptbase64(signature.sign()); 
 } 
 
  
 private static String encryptbase64(byte[] data) { 
 base64Encoder encoder = new base64Encoder(); 
 String encode = encoder.encode(data); 
 return encode; 
 } 
 
  
 private static byte[] decryptbase64(String data) throws Exception { 
 base64Decoder decoder = new base64Decoder(); 
 byte[] buffer = decoder.decodeBuffer(data); 
 return buffer; 
 } 
 
  
 public static boolean verify(byte[] data, String publicKey, String sign) throws Exception { 
 byte[] keyBytes = decryptbase64(publicKey); 
 X509EncodedKeySpec keySpec = new X509EncodedKeySpec(keyBytes); 
 KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM); 
 PublicKey pubKey = keyFactory.generatePublic(keySpec); 
  
 Signature signature = Signature.getInstance(SIGNATURE_ALGORITHM); 
 signature.initVerify(pubKey); 
 signature.update(data); 
  
 return signature.verify(decryptbase64(sign)); //验证签名 
 } 
 
}