example/src/com/fr/privilege/RSAUtil.java

package com.fr.privilege;

import javax.crypto.Cipher;
import java.io.ByteArrayOutputStream;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.math.BigInteger;
import java.security.KeyFactory;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.NoSuchAlgorithmException;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.SecureRandom;
import java.security.interfaces.RSAPrivateKey;
import java.security.interfaces.RSAPublicKey;
import java.security.spec.InvalidKeySpecException;
import java.security.spec.RSAPrivateKeySpec;
import java.security.spec.RSAPublicKeySpec;

/**
 * RSA 工具类。提供加密，解密，生成密钥对等方法。
 * 需要到http://www.bouncycastle.org下载bcprov-jdk14-123.jar。
 */
public class RSAUtil {
    /**
     * * 生成密钥对 *
     *
     * @return KeyPair *
     * @throws EncryptException
     */
    public static KeyPair generateKeyPair() throws Exception {
        try {
            KeyPairGenerator keyPairGen = KeyPairGenerator.getInstance("RSA",
                    new org.bouncycastle.jce.provider.BouncyCastleProvider());
            final int KEY_SIZE = 1024;// 没什么好说的了，这个值关系到块加密的大小，可以更改，但是不要太大，否则效率会低
            keyPairGen.initialize(KEY_SIZE, new SecureRandom());
            KeyPair keyPair = keyPairGen.generateKeyPair();
            saveKeyPair(keyPair);
            return keyPair;
        } catch (Exception e) {
            throw new Exception(e.getMessage());
        }
    }

    public static KeyPair getKeyPair() throws Exception {
        FileInputStream fis = new FileInputStream("C:/RSAKey.txt");
        ObjectInputStream oos = new ObjectInputStream(fis);
        KeyPair kp = (KeyPair) oos.readObject();
        oos.close();
        fis.close();
        return kp;
    }

    public static void saveKeyPair(KeyPair kp) throws Exception {

        FileOutputStream fos = new FileOutputStream("C:/RSAKey.txt");
        ObjectOutputStream oos = new ObjectOutputStream(fos);
        // 生成密钥
        oos.writeObject(kp);
        oos.close();
        fos.close();
    }

    /**
     * * 生成公钥 *
     *
     * @param modulus        *
     * @param publicExponent *
     * @return RSAPublicKey *
     * @throws Exception
     */
    public static RSAPublicKey generateRSAPublicKey(byte[] modulus,
                                                    byte[] publicExponent) throws Exception {
        KeyFactory keyFac = null;
        try {
            keyFac = KeyFactory.getInstance("RSA",
                    new org.bouncycastle.jce.provider.BouncyCastleProvider());
        } catch (NoSuchAlgorithmException ex) {
            throw new Exception(ex.getMessage());
        }

        RSAPublicKeySpec pubKeySpec = new RSAPublicKeySpec(new BigInteger(
                modulus), new BigInteger(publicExponent));
        try {
            return (RSAPublicKey) keyFac.generatePublic(pubKeySpec);
        } catch (InvalidKeySpecException ex) {
            throw new Exception(ex.getMessage());
        }
    }

    /**
     * * 生成私钥 *
     *
     * @param modulus         *
     * @param privateExponent *
     * @return RSAPrivateKey *
     * @throws Exception
     */
    public static RSAPrivateKey generateRSAPrivateKey(byte[] modulus,
                                                      byte[] privateExponent) throws Exception {
        KeyFactory keyFac = null;
        try {
            keyFac = KeyFactory.getInstance("RSA",
                    new org.bouncycastle.jce.provider.BouncyCastleProvider());
        } catch (NoSuchAlgorithmException ex) {
            throw new Exception(ex.getMessage());
        }

        RSAPrivateKeySpec priKeySpec = new RSAPrivateKeySpec(new BigInteger(
                modulus), new BigInteger(privateExponent));
        try {
            return (RSAPrivateKey) keyFac.generatePrivate(priKeySpec);
        } catch (InvalidKeySpecException ex) {
            throw new Exception(ex.getMessage());
        }
    }

    /**
     * * 加密 *
     *
     * @param key  加密的密钥 *
     * @param data 待加密的明文数据 *
     * @return 加密后的数据 *
     * @throws Exception
     */
    public static byte[] encrypt(PublicKey pk, byte[] data) throws Exception {
        try {
            Cipher cipher = Cipher.getInstance("RSA",
                    new org.bouncycastle.jce.provider.BouncyCastleProvider());
            cipher.init(Cipher.ENCRYPT_MODE, pk);
            int blockSize = cipher.getBlockSize();// 获得加密块大小，如：加密前数据为128个byte，而key_size=1024
            // 加密块大小为127
            // byte,加密后为128个byte;因此共有2个加密块，第一个127
            // byte第二个为1个byte
            int outputSize = cipher.getOutputSize(data.length);// 获得加密块加密后块大小
            int leavedSize = data.length % blockSize;
            int blocksSize = leavedSize != 0 ? data.length / blockSize + 1
                    : data.length / blockSize;
            byte[] raw = new byte[outputSize * blocksSize];
            int i = 0;
            while (data.length - i * blockSize > 0) {
                if (data.length - i * blockSize > blockSize)
                    cipher.doFinal(data, i * blockSize, blockSize, raw, i
                            * outputSize);
                else
                    cipher.doFinal(data, i * blockSize, data.length - i
                            * blockSize, raw, i * outputSize);
                // 这里面doUpdate方法不可用，查看源代码后发现每次doUpdate后并没有什么实际动作除了把byte[]放到
                // ByteArrayOutputStream中，而最后doFinal的时候才将所有的byte[]进行加密，可是到了此时加密块大小很可能已经超出了
                // OutputSize所以只好用dofinal方法。

                i++;
            }
            return raw;
        } catch (Exception e) {
            throw new Exception(e.getMessage());
        }
    }

    /**
     * * 解密 *
     *
     * @param key 解密的密钥 *
     * @param raw 已经加密的数据 *
     * @return 解密后的明文 *
     * @throws Exception
     */
    public static byte[] decrypt(PrivateKey pk, byte[] raw) throws Exception {
        try {
            Cipher cipher = Cipher.getInstance("RSA",
                    new org.bouncycastle.jce.provider.BouncyCastleProvider());
            cipher.init(cipher.DECRYPT_MODE, pk);
            int blockSize = cipher.getBlockSize();
            ByteArrayOutputStream bout = new ByteArrayOutputStream(64);
            int j = 0;

            while (raw.length - j * blockSize > 0) {
                bout.write(cipher.doFinal(raw, j * blockSize, blockSize));
                j++;
            }
            return bout.toByteArray();
        } catch (Exception e) {
            throw new Exception(e.getMessage());
        }
    }

    /**
     * * *
     *
     * @param args *
     * @throws Exception
     */
    public static void main(String[] args) throws Exception {
        RSAPublicKey rsap = (RSAPublicKey) RSAUtil.generateKeyPair()
                .getPublic();
        String test = "hello world";
        byte[] en_test = encrypt(getKeyPair().getPublic(), test.getBytes());
        System.out.println("123:" + new String(en_test));
        byte[] de_test = decrypt(getKeyPair().getPrivate(), en_test);
        System.out.println(new String(de_test));
    }
}