java RSA公钥加密，私钥解密算法例子.

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RSA 是一种非对称加密算法，一般很难破解，因此一些要求比较高的系统通常会采用rsa加密算法，一般来说用RSA加密有如下几个步骤.
1. 生成公钥与私钥
2. 用公钥对需要加密的字符串等进行加密
3. 在需要解密的地方，用私钥进行解密
下面对上面的几个部分贴出代码.

1. 生成公钥与私钥

 程序代码

package com.rsa;
import java.io.FileOutputStream; 
import java.security.KeyPair; 
import java.security.KeyPairGenerator; 
import java.security.SecureRandom; 
import java.util.Date;

public class GenKeys {
    public static void main(String[] args) throws Exception {
        KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance("RSA"); 
        SecureRandom secureRandom = new SecureRandom(new Date().toString().getBytes());
        keyPairGenerator.initialize(1024, secureRandom);
        KeyPair keyPair = keyPairGenerator.genKeyPair();
        String publicKeyFilename = "D:/publicKeyFile";
        byte[] publicKeyBytes = keyPair.getPublic().getEncoded();
        FileOutputStream fos = new FileOutputStream(publicKeyFilename); 
        fos.write(publicKeyBytes); 
        fos.close();
        String privateKeyFilename = "D:/privateKeyFile"; 
        byte[] privateKeyBytes = keyPair.getPrivate().getEncoded();
        fos = new FileOutputStream(privateKeyFilename); 
        fos.write(privateKeyBytes); 
        fos.close();
    }
}

2. 读取公钥方法

 程序代码

package com.rsa;

import java.io.DataInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.security.PublicKey;
import java.security.spec.X509EncodedKeySpec;
import java.security.KeyFactory;

public class PublicKeyReader {    
    public static PublicKey get(String filename) throws Exception {
        File f = new File(filename);
        FileInputStream fis = new FileInputStream(f); 
        DataInputStream dis = new DataInputStream(fis);
        byte[] keyBytes = new byte[(int)f.length()]; 
        dis.readFully(keyBytes); 
        dis.close();
        X509EncodedKeySpec spec = new X509EncodedKeySpec(keyBytes);
        KeyFactory kf = KeyFactory.getInstance("RSA"); 
        return kf.generatePublic(spec);
    }


}

3.读取私钥方法

 程序代码

package com.rsa;

import java.io.DataInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.security.KeyFactory;
import java.security.PrivateKey;
import java.security.spec.InvalidKeySpecException;
import java.security.spec.PKCS8EncodedKeySpec;
public class PrivateKeyReader {    
    public static PrivateKey get(String filename)throws Exception {
        File f = new File(filename);
        FileInputStream fis = new FileInputStream(f);
        DataInputStream dis = new DataInputStream(fis);
        byte[] keyBytes = new byte[(int)f.length()];
        dis.readFully(keyBytes);
        dis.close();
        PKCS8EncodedKeySpec spec =new PKCS8EncodedKeySpec(keyBytes);
        KeyFactory kf = KeyFactory.getInstance("RSA");
        return kf.generatePrivate(spec);
      }

    
    public static void main(String[] args) throws Exception, InvalidKeySpecException, IOException {
        PrivateKeyReader.get("d:/privateKeyFile");
    }
}

4. 测试公钥加密，私钥解密

 程序代码

package com.rsa;

import java.security.interfaces.RSAPrivateKey;
import java.security.interfaces.RSAPublicKey;
import javax.crypto.Cipher;

public class TestEncryptAndDecrypt {    
    public static void main(String[] args) throws Exception {
        String input = "thisIsMyPassword$7788";
        Cipher cipher = Cipher.getInstance("RSA");        
        RSAPublicKey pubKey = (RSAPublicKey) PublicKeyReader.get("d:/publicKeyFile");
        RSAPrivateKey privKey = (RSAPrivateKey) PrivateKeyReader.get("d:/privateKeyFile");
        cipher.init(Cipher.ENCRYPT_MODE, pubKey);
        byte[] cipherText = cipher.doFinal(input.getBytes());
        //加密后的东西
        System.out.println("cipher: " + new String(cipherText));        
        //开始解密
        cipher.init(Cipher.DECRYPT_MODE, privKey); 
        byte[] plainText = cipher.doFinal(cipherText);
        System.out.println("plain : " + new String(plainText));
    }

}

查看结果:

 程序代码

cipher: J???
?nE??J?b9??CO??I???g[B{?w??u0????}?r6
?Q??Xa???????N}n?]?@??_9!D??_?|k??&g?^????XTa$?7??*?{7?R???v?S
plain : thisIsMyPassword$7788

说明加密解密成功。

备注，这里记录的只是测试方法，当然在实际使用过程中，可能还需要 对加密后的 byte[] 采用 base64 编码，转换成字符串存储起来，在解密的时候，先通过 base64 还原成 byte, 然后在解密，这样会更好。详细的方法，

可以参考这篇文章 ：http://www.yihaomen.com/article/java/376.htm

java RSA公钥加密，私钥解密算法例子.

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原文地址：http://my.oschina.net/u/2284972/blog/525301