JAVA实现RSA加密解密 非对称算法

首先RSA是一个非对称的加密算法。所以在使用该算法加密解密之前，必须先行生成密钥对。包含公钥和私钥

JDK中提供了生成密钥对的类KeyPairGenerator，实比例如以下：

public static Map<String, Object> genKeyPair() throws Exception {
		// 获取公钥私钥密钥对的生成器
		KeyPairGenerator kpg = KeyPairGenerator.getInstance("RSA");
		// 初始化确定密钥大小的密钥生成器
		kpg.initialize(1024);
		// 生成密钥对
		KeyPair kp = kpg.generateKeyPair();
		RSAPublicKey publicKey = (RSAPublicKey) kp.getPublic();
		RSAPrivateKey privateKey = (RSAPrivateKey) kp.getPrivate();
		Map<String, Object> keyMap = new HashMap<String, Object>();
		keyMap.put(PUBLIC_KEY, publicKey);
		keyMap.put(PRIVATE_KEY, privateKey);
		return keyMap;
	}

以上这段代码返回的是一个Map类型的数据。当中存储了公钥和私钥

当你完毕了密钥对的生成之后，你就能够将公钥公开出去了。让相关的加密程序通过该公钥对实施RSA加密

public static byte[] encryptByPublicKey(byte[] data, String publicKey)
            throws Exception {
        //data即是待加密的数据String.getBytes就可以
        byte[] keyBytes = Base64Utils.decode(publicKey);
        //依据指定的编码密钥创建一个新的X509EncodedKeySpec
        X509EncodedKeySpec x509KeySpec = new X509EncodedKeySpec(keyBytes);
        KeyFactory keyFactory = KeyFactory.getInstance(ENCRYPT_ALGORITHM);
        //依据提供的密钥规范生成公钥对象
        Key publicK = keyFactory.generatePublic(x509KeySpec);
        // 对数据加密
        Cipher cipher = Cipher.getInstance(keyFactory.getAlgorithm());
        //用密钥初始化加密模式的cipher。全部后面的doFinal方法做的是加密
        cipher.init(Cipher.ENCRYPT_MODE, publicK);
        int inputLen = data.length;
        ByteArrayOutputStream out = new ByteArrayOutputStream();
        int offSet = 0;
        byte[] cache;
        int i = 0;
        // 对数据分段加密
        while (inputLen - offSet > 0) {
            if (inputLen - offSet > MAX_ENCRYPT_BLOCK) {//一次加密的字节长度
                cache = cipher.doFinal(data, offSet, MAX_ENCRYPT_BLOCK);
            } else {
                cache = cipher.doFinal(data, offSet, inputLen - offSet);
            }
            out.write(cache, 0, cache.length);
            i++;
            offSet = i * MAX_ENCRYPT_BLOCK;
        }
        byte[] encryptedData = out.toByteArray();
        out.close();
        return encryptedData;
    }

加密完毕之后通过自己的私钥对密文进行解密

public static byte[] decryptByPrivateKey(byte[] data, String privateKey)
			throws Exception {
		byte[] keyBytes = Base64Utils.decode(privateKey);
		PKCS8EncodedKeySpec pkcs8KeySpec = new PKCS8EncodedKeySpec(keyBytes);
		KeyFactory keyFactory = KeyFactory.getInstance(ENCRYPT_ALGORITHM);
		Key privateK = keyFactory.generatePrivate(pkcs8KeySpec);
		Cipher cipher = Cipher.getInstance(keyFactory.getAlgorithm());
		cipher.init(Cipher.DECRYPT_MODE, privateK);
		int inputLen = data.length;
		ByteArrayOutputStream out = new ByteArrayOutputStream();
		int offSet = 0;
		byte[] cache;
		int i = 0;
		// 对数据分段解密
		while (inputLen - offSet > 0) {
			if (inputLen - offSet > MAX_DECRYPT_BLOCK) {
				cache = cipher.doFinal(data, offSet, MAX_DECRYPT_BLOCK);
			} else {
				cache = cipher.doFinal(data, offSet, inputLen - offSet);
			}
			out.write(cache, 0, cache.length);
			i++;
			offSet = i * MAX_DECRYPT_BLOCK;
		}
		byte[] decryptedData = out.toByteArray();
		out.close();
		return decryptedData;
	}

生成密钥对：

try {
			Map<String, Object> keyMap = RSAUtils.genKeyPair();
			publicKey = RSAUtils.getPublicKey(keyMap);
			privateKey = RSAUtils.getPrivateKey(keyMap);
			System.out.println("公钥-->" + publicKey);
			System.out.println("私钥-->" + privateKey);
		} catch (Exception e) {
			e.printStackTrace();
		}

执行结果展示：

公钥-->MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQCjJOdVRlDN/5nWHmpFtc9XffgmT2SAj7b+yBk55HSr1iQQt5k8/4O5qdnk3qxhgIgWuSyDpxR2FK5dzfXsomjc0L2CZGaStAkbbvw1wbOSYo11cxNpkphn3PIVbuBxrpEuCJ4HrMKTuBk662aA0ysxy2/BrK4NXxtRlMxI+/BYsQIDAQAB
私钥-->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

利用公钥加密。私钥解密：

System.out.println("公钥加密——私钥解密");
		System.out.println("加密前数据的内容是-->" + sourceStr);
		byte[] data = sourceStr.getBytes();
		byte[] encryptData = RSAUtils.encryptByPublicKey(data, publicKey);
		System.out.println("加密后的数据内容是-->" + new String(encryptData));
		byte[] decryptData = RSAUtils.decryptByPrivateKey(encryptData,
				privateKey);
		System.out.println("解密后的数据内容是-->" + new String(decryptData));

公钥加密——私钥解密
加密前数据的内容是-->这是一段待加密的数据
加密后的数据内容是-->(���%5    [�͖W��uA- ��m�u�&w�2��gQ���-5�Q���`7:Й�C,�8t�qM�gJ��e2"�)y��͓�����    �Y��@�y*_�M�����x*;�f1���v֚�@�h�}P?X�2
解密后的数据内容是-->这是一段待加密的数据

附Base64Utils.java

package rsa;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.OutputStream;

public class Base64Utils {
	private static final char[] legalChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/".toCharArray();

	/**
	 * data[]进行编码
	 * 
	 * @param data
	 * @return
	 */
	public static String encode(byte[] data) {
		int start = 0;
		int len = data.length;
		StringBuffer buf = new StringBuffer(data.length * 3 / 2);

		int end = len - 3;
		int i = start;
		int n = 0;

		while (i <= end) {
			int d = ((((int) data[i]) & 0x0ff) << 16) | ((((int) data[i + 1]) & 0x0ff) << 8) | (((int) data[i + 2]) & 0x0ff);

			buf.append(legalChars[(d >> 18) & 63]);
			buf.append(legalChars[(d >> 12) & 63]);
			buf.append(legalChars[(d >> 6) & 63]);
			buf.append(legalChars[d & 63]);

			i += 3;

			if (n++ >= 14) {
				n = 0;
				buf.append(" ");
			}
		}

		if (i == start + len - 2) {
			int d = ((((int) data[i]) & 0x0ff) << 16) | ((((int) data[i + 1]) & 255) << 8);

			buf.append(legalChars[(d >> 18) & 63]);
			buf.append(legalChars[(d >> 12) & 63]);
			buf.append(legalChars[(d >> 6) & 63]);
			buf.append("=");
		} else if (i == start + len - 1) {
			int d = (((int) data[i]) & 0x0ff) << 16;

			buf.append(legalChars[(d >> 18) & 63]);
			buf.append(legalChars[(d >> 12) & 63]);
			buf.append("==");
		}

		return buf.toString();
	}

	private static int decode(char c) {
		if (c >= 'A' && c <= 'Z')
			return ((int) c) - 65;
		else if (c >= 'a' && c <= 'z')
			return ((int) c) - 97 + 26;
		else if (c >= '0' && c <= '9')
			return ((int) c) - 48 + 26 + 26;
		else
			switch (c) {
			case '+':
				return 62;
			case '/':
				return 63;
			case '=':
				return 0;
			default:
				throw new RuntimeException("unexpected code: " + c);
			}
	}

	/**
	 * Decodes the given Base64 encoded String to a new byte array. The byte array holding the decoded data is returned.
	 */

	public static byte[] decode(String s) {

		ByteArrayOutputStream bos = new ByteArrayOutputStream();
		try {
			decode(s, bos);
		} catch (IOException e) {
			throw new RuntimeException();
		}
		byte[] decodedBytes = bos.toByteArray();
		try {
			bos.close();
			bos = null;
		} catch (IOException ex) {
			System.err.println("Error while decoding BASE64: " + ex.toString());
		}
		return decodedBytes;
	}

	private static void decode(String s, OutputStream os) throws IOException {
		int i = 0;

		int len = s.length();

		while (true) {
			while (i < len && s.charAt(i) <= ' ')
				i++;

			if (i == len)
				break;

			int tri = (decode(s.charAt(i)) << 18) + (decode(s.charAt(i + 1)) << 12) + (decode(s.charAt(i + 2)) << 6) + (decode(s.charAt(i + 3)));

			os.write((tri >> 16) & 255);
			if (s.charAt(i + 2) == '=')
				break;
			os.write((tri >> 8) & 255);
			if (s.charAt(i + 3) == '=')
				break;
			os.write(tri & 255);

			i += 4;
		}
	}
	
	/**
	 * data[]进行编码
	 * 
	 * @param data
	 * @return
	 */
	public static String Base64Encoder(byte[] data) {
		int start = 0;
		int len = data.length;
		StringBuffer buf = new StringBuffer(data.length * 3 / 2);

		int end = len - 3;
		int i = start;
		int n = 0;

		while (i <= end) {
			int d = ((((int) data[i]) & 0x0ff) << 16) | ((((int) data[i + 1]) & 0x0ff) << 8) | (((int) data[i + 2]) & 0x0ff);

			buf.append(legalChars[(d >> 18) & 63]);
			buf.append(legalChars[(d >> 12) & 63]);
			buf.append(legalChars[(d >> 6) & 63]);
			buf.append(legalChars[d & 63]);

			i += 3;

			if (n++ >= 14) {
				//不须要空格
				n = 0;
			}
		}

		if (i == start + len - 2) {
			int d = ((((int) data[i]) & 0x0ff) << 16) | ((((int) data[i + 1]) & 255) << 8);

			buf.append(legalChars[(d >> 18) & 63]);
			buf.append(legalChars[(d >> 12) & 63]);
			buf.append(legalChars[(d >> 6) & 63]);
			buf.append("=");
		} else if (i == start + len - 1) {
			int d = (((int) data[i]) & 0x0ff) << 16;

			buf.append(legalChars[(d >> 18) & 63]);
			buf.append(legalChars[(d >> 12) & 63]);
			buf.append("==");
		}

		return buf.toString();
	}
	
}