Java RSA加密/解密

Java RSA加密&解密如下：

import sun.misc.BASE64Decoder;
import sun.misc.BASE64Encoder;

import javax.crypto.Cipher;
import java.io.IOException;
import java.nio.charset.Charset;
import java.security.*;
import java.security.interfaces.RSAPrivateKey;
import java.security.interfaces.RSAPublicKey;
import java.security.spec.InvalidKeySpecException;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;

public class Sample {
    public static final String RSA_ALGORITHM = "RSA";
    public static final Charset UTF8 = Charset.forName("UTF-8");

    public static void main(String [] args) throws Exception {
        // generate public and private keys
        KeyPair keyPair = buildKeyPair();
        PublicKey publicKey = keyPair.getPublic();
        PrivateKey privateKey = keyPair.getPrivate();

        // encrypt the message
        byte [] encrypted = encrypt(privateKey, "This is a secret message");     
        System.out.println(base64Encode(encrypted));  // <>
        
        // decrypt the message
        byte[] secret = decrypt(publicKey, encrypted);
        System.out.println(new String(secret, UTF8));     // This is a secret message
    }

    public static KeyPair buildKeyPair() throws NoSuchAlgorithmException {
        final int keySize = 2048;
        KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance(RSA_ALGORITHM);
        keyPairGenerator.initialize(keySize);
        return keyPairGenerator.genKeyPair();
    }

    public static byte[] encrypt(PrivateKey privateKey, String message) throws Exception {
        Cipher cipher = Cipher.getInstance(RSA_ALGORITHM);
        cipher.init(Cipher.ENCRYPT_MODE, privateKey);  

        return cipher.doFinal(message.getBytes(UTF8));
    }
    
    public static byte[] decrypt(PublicKey publicKey, byte [] encrypted) throws Exception {
        Cipher cipher = Cipher.getInstance(RSA_ALGORITHM);
        cipher.init(Cipher.DECRYPT_MODE, publicKey);
        
        return cipher.doFinal(encrypted);
    }

    public static String base64Encode(byte[] data) {
        return new BASE64Encoder().encode(data);
    }
    public static byte[] base64Decode(String data) throws IOException {
        return new BASE64Decoder().decodeBuffer(data);
    }
}

拿到RSA 公钥和私钥后我们可以保存到文件中，代码如下：

    public void savePublicKey(PublicKey publicKey) throws IOException {
        // 得到公钥字符串
        String publicKeyString = base64Encode(publicKey.getEncoded());
        System.out.println("publicKeyString="+publicKeyString);
        FileWriter fw = new FileWriter("publicKey.keystore");
        BufferedWriter bw = new BufferedWriter(fw);
        bw.write(publicKeyString);
        bw.close();
    }

    public void savePrivateKey(PrivateKey privateKey) throws IOException {
        // 得到私钥字符串
        String privateKeyString = base64Encode(privateKey.getEncoded());
        System.out.println("privateKeyString="+privateKeyString);

        FileWriter fw = new FileWriter("privateKey.keystore");
        BufferedWriter bw = new BufferedWriter(fw);
        bw.write(privateKeyString);
        bw.close();
    }

    public static String base64Encode(byte[] data) {
        return new BASE64Encoder().encode(data);
    }
    public static byte[] base64Decode(String data) throws IOException {
        return new BASE64Decoder().decodeBuffer(data);
    }

解析已有的公钥和私钥，代码如下：

    public static RSAPublicKey loadPublicKey(String publicKeyStr) throws Exception {
        try {
            byte[] buffer = base64Decode(publicKeyStr);
            KeyFactory keyFactory = KeyFactory.getInstance(RSA_ALGORITHM);
            X509EncodedKeySpec keySpec = new X509EncodedKeySpec(buffer);
            return (RSAPublicKey) keyFactory.generatePublic(keySpec);
        } catch (NoSuchAlgorithmException e) {
            throw new RuntimeException(e);
        } catch (InvalidKeySpecException e) {
            throw new RuntimeException(e);
        }
    }

    public static RSAPrivateKey loadPrivateKey(String privateKeyStr) throws Exception {
        try {
            byte[] buffer = base64Decode(privateKeyStr);
            PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(buffer);
            KeyFactory keyFactory = KeyFactory.getInstance(RSA_ALGORITHM);
            return (RSAPrivateKey) keyFactory.generatePrivate(keySpec);
        } catch (NoSuchAlgorithmException e) {
            throw new RuntimeException(e);
        } catch (InvalidKeySpecException e) {
            throw new RuntimeException(e);
        }
    }

    public static String base64Encode(byte[] data) {
        return new BASE64Encoder().encode(data);
    }
    public static byte[] base64Decode(String data) throws IOException {
        return new BASE64Decoder().decodeBuffer(data);
    }

完整代码如下：

package util;

import sun.misc.BASE64Decoder;
import sun.misc.BASE64Encoder;

import javax.crypto.Cipher;
import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.IOException;
import java.nio.charset.Charset;
import java.security.*;
import java.security.interfaces.RSAPrivateKey;
import java.security.interfaces.RSAPublicKey;
import java.security.spec.InvalidKeySpecException;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;

public class Sample {
    public static final String RSA_ALGORITHM = "RSA";
    public static final Charset UTF8 = Charset.forName("UTF-8");

    public static void main(String [] args) throws Exception {
        // generate public and private keys
        KeyPair keyPair = buildKeyPair();
        PublicKey publicKey = keyPair.getPublic();
        PrivateKey privateKey = keyPair.getPrivate();

        // encrypt the message
        byte [] encrypted = encrypt(privateKey, "This is a secret message");     
        System.out.println(base64Encode(encrypted));  // <>
        
        // decrypt the message
        byte[] secret = decrypt(publicKey, encrypted);
        System.out.println(new String(secret, UTF8));     // This is a secret message
    }

    public static KeyPair buildKeyPair() throws NoSuchAlgorithmException {
        final int keySize = 2048;
        KeyPairGenerator keyPairGenerator = KeyPairGenerator.getInstance(RSA_ALGORITHM);
        keyPairGenerator.initialize(keySize);
        return keyPairGenerator.genKeyPair();
    }

    public static byte[] encrypt(PrivateKey privateKey, String message) throws Exception {
        Cipher cipher = Cipher.getInstance(RSA_ALGORITHM);
        cipher.init(Cipher.ENCRYPT_MODE, privateKey);  

        return cipher.doFinal(message.getBytes(UTF8));
    }
    
    public static byte[] decrypt(PublicKey publicKey, byte [] encrypted) throws Exception {
        Cipher cipher = Cipher.getInstance(RSA_ALGORITHM);
        cipher.init(Cipher.DECRYPT_MODE, publicKey);
        
        return cipher.doFinal(encrypted);
    }

    /**
     * 从字符串中加载公钥
     *
     */
    public static RSAPublicKey loadPublicKey(String publicKeyStr) throws Exception {
        try {
            byte[] buffer = base64Decode(publicKeyStr);
            KeyFactory keyFactory = KeyFactory.getInstance(RSA_ALGORITHM);
            X509EncodedKeySpec keySpec = new X509EncodedKeySpec(buffer);
            return (RSAPublicKey) keyFactory.generatePublic(keySpec);
        } catch (NoSuchAlgorithmException e) {
            throw new RuntimeException(e);
        } catch (InvalidKeySpecException e) {
            throw new RuntimeException(e);
        }
    }

    public static RSAPrivateKey loadPrivateKey(String privateKeyStr) throws Exception {
        try {
            byte[] buffer = base64Decode(privateKeyStr);
            PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(buffer);
            KeyFactory keyFactory = KeyFactory.getInstance(RSA_ALGORITHM);
            return (RSAPrivateKey) keyFactory.generatePrivate(keySpec);
        } catch (NoSuchAlgorithmException e) {
            throw new RuntimeException(e);
        } catch (InvalidKeySpecException e) {
            throw new RuntimeException(e);
        }
    }

    public void savePublicKey(PublicKey publicKey) throws IOException {
        // 得到公钥字符串
        String publicKeyString = base64Encode(publicKey.getEncoded());
        System.out.println("publicKeyString="+publicKeyString);
        FileWriter fw = new FileWriter("publicKey.keystore");
        BufferedWriter bw = new BufferedWriter(fw);
        bw.write(publicKeyString);
        bw.close();
    }

    public void savePrivateKey(PrivateKey privateKey) throws IOException {
        // 得到私钥字符串
        String privateKeyString = base64Encode(privateKey.getEncoded());
        System.out.println("privateKeyString="+privateKeyString);

        BufferedWriter bw = new BufferedWriter(new FileWriter("privateKey.keystore"));
        bw.write(privateKeyString);
        bw.close();
    }

    public static String base64Encode(byte[] data) {
        return new BASE64Encoder().encode(data);
    }
    public static byte[] base64Decode(String data) throws IOException {
        return new BASE64Decoder().decodeBuffer(data);
    }
}