RSA加密解密

实际分析所得 ：简单来说加密，那肯定是不希望数据被人看到，所以只有自己能解密，所以公钥负责加密，私钥负责解密；同理，既然是签名，那肯定是不希望有人冒充我发消息，只有我才能发布这个签名，所以可得出私钥负责签名，公钥负责验证

import java.io.ByteArrayOutputStream;
import java.math.BigInteger;
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.Signature;
import java.security.interfaces.RSAPrivateKey;
import java.security.interfaces.RSAPublicKey;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.RSAPrivateKeySpec;
import java.security.spec.RSAPublicKeySpec;
import java.security.spec.X509EncodedKeySpec;
import java.util.HashMap;
import java.util.Map;

import javax.crypto.Cipher;

import org.apache.commons.codec.binary.Base64;

/**
 * <p>
 * RSA公钥/私钥/签名(1024)工具包 字符串格式的密钥在未在特殊说明情况下都为hex编码格式<br/>
 * 由于非对称加密速度缓慢，一般文件不使用它来加密而是使用对称加密，<br/>
 * 非对称加密算法可以用来对对称加密的密钥加密，这样保证密钥的安全也就保证了数据的安全
 */
public class RSAUtil {

    /**
     * 加密算法RSA
     */
    public static final String KEY_ALGORITHM = "RSA";
    /**
     * 签名算法
     */
    public static final String SIGNATURE_ALGORITHM = "SHA256withRSA";
    /**
     * 获取公钥的key
     */
    private static final String PUBLIC_KEY = "RSAPublicKey";
    /**
     * 获取私钥的key
     */
    private static final String PRIVATE_KEY = "RSAPrivateKey";
    private static final String CHARACTER_ENCODEING = "UTF-8";
    /**
     * RSA最大加密明文大小
     */
    private static final int MAX_ENCRYPT_BLOCK = 117;
    /**
     * RSA最大解密密文大小
     */
    private static final int MAX_DECRYPT_BLOCK = 128;

    /**
     * <p>
     * 生成密钥对(公钥和私钥)
     * </p>
     * 
     * @return
     * @throws Exception
     */
    public static Map<String, Object> genKeyPair() throws Exception {
        KeyPairGenerator keyPairGen = KeyPairGenerator.getInstance(KEY_ALGORITHM);
        keyPairGen.initialize(1024);// 128位
        KeyPair keyPair = keyPairGen.generateKeyPair();
        RSAPublicKey publicKey = (RSAPublicKey) keyPair.getPublic();
        RSAPrivateKey privateKey = (RSAPrivateKey) keyPair.getPrivate();
        Map<String, Object> keyMap = new HashMap<String, Object>(2);
        keyMap.put(PUBLIC_KEY, publicKey);
        keyMap.put(PRIVATE_KEY, privateKey);
        return keyMap;
    }

    /**
     * <p>
     * 用私钥对信息生成数字签名
     * </p>
     * 
     * @param data
     *            已加密数据
     * @param privateKey
     *            私钥(hex编码)
     * 
     * @return
     * @throws Exception
     */
    public static String sign(String src, String privateKey) throws Exception {
        byte[] keyBytes = Base64.decodeBase64(privateKey);
        PKCS8EncodedKeySpec pkcs8KeySpec = new PKCS8EncodedKeySpec(keyBytes);
        KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);
        PrivateKey privateK = keyFactory.generatePrivate(pkcs8KeySpec);
        Signature signature = Signature.getInstance(SIGNATURE_ALGORITHM);
        signature.initSign(privateK);
        byte[] data = src.getBytes(CHARACTER_ENCODEING);
        signature.update(data);
        return Base64.encodeBase64URLSafeString(signature.sign());
    }

    /**
     * <p>
     * 校验数字签名
     * </p>
     * 
     * @param data
     *            已加密数据
     * @param publicKey
     *            公钥(hex编码)
     * @param sign
     *            数字签名
     * 
     * @return
     * @throws Exception
     * 
     */
    public static boolean verify(String src, String publicKey, String sign) throws Exception {
        byte[] keyBytes = Base64.decodeBase64(publicKey);
        X509EncodedKeySpec keySpec = new X509EncodedKeySpec(keyBytes);
        KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);
        PublicKey publicK = keyFactory.generatePublic(keySpec);
        Signature signature = Signature.getInstance(SIGNATURE_ALGORITHM);
        signature.initVerify(publicK);
        signature.update(src.getBytes(CHARACTER_ENCODEING));
        return signature.verify(Base64.decodeBase64(sign));
    }

    public static String encrypt(String s, String publicKey) throws Exception {
        byte[] keyBytes = Base64.decodeBase64(publicKey);
        X509EncodedKeySpec keySpec = new X509EncodedKeySpec(keyBytes);
        KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);
        PublicKey publicK = keyFactory.generatePublic(keySpec);
        Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
        cipher.init(Cipher.ENCRYPT_MODE, publicK);
        return Base64.encodeBase64URLSafeString(cipher.doFinal(s.getBytes(CHARACTER_ENCODEING)));
    }

    /**
     * <P>
     * 私钥解密
     * </p>
     * 
     * @param encryptedData
     *            已加密数据
     * @param privateKey
     *            私钥(hex编码)
     * @return
     * @throws Exception
     */
    public static String decryptByPrivateKey(String src, String privateKey) throws Exception {
        byte[] keyBytes = Base64.decodeBase64(privateKey);
        PKCS8EncodedKeySpec pkcs8KeySpec = new PKCS8EncodedKeySpec(keyBytes);
        KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);
        Key privateK = keyFactory.generatePrivate(pkcs8KeySpec);
        Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
        cipher.init(Cipher.DECRYPT_MODE, privateK);
        byte[] encryptedData = Base64.decodeBase64(src);
        int inputLen = encryptedData.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(encryptedData, offSet, MAX_DECRYPT_BLOCK);
            } else {
                cache = cipher.doFinal(encryptedData, offSet, inputLen - offSet);
            }
            out.write(cache, 0, cache.length);
            i++;
            offSet = i * MAX_DECRYPT_BLOCK;
        }
        byte[] decryptedData = out.toByteArray();
        out.close();
        return new String(decryptedData, CHARACTER_ENCODEING);
    }

    /**
     * <p>
     * 公钥解密
     * </p>
     * 
     * @param encryptedData已加密数据
     *            (hex编码)
     * @param publicKey公钥
     *            (hex编码)
     * @return
     * @throws Exception
     */
    public static String decryptByPublicKey(String src, String publicKey) throws Exception {
        byte[] keyBytes = Base64.decodeBase64(publicKey);
        X509EncodedKeySpec x509KeySpec = new X509EncodedKeySpec(keyBytes);
        KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);
        Key publicK = keyFactory.generatePublic(x509KeySpec);
        Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
        cipher.init(Cipher.DECRYPT_MODE, publicK);
        byte[] encryptedData = Base64.decodeBase64(src);
        int inputLen = encryptedData.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(encryptedData, offSet, MAX_DECRYPT_BLOCK);
            } else {
                cache = cipher.doFinal(encryptedData, offSet, inputLen - offSet);
            }
            out.write(cache, 0, cache.length);
            i++;
            offSet = i * MAX_DECRYPT_BLOCK;
        }
        byte[] decryptedData = out.toByteArray();
        out.close();
        return new String(decryptedData, CHARACTER_ENCODEING);
    }

    /**
     * <P>
     * 私钥解密
     * 
     * @param encryptedData
     *            已加密数据
     * @param privateKey
     *            私钥(hex编码)
     * @return
     * @throws Exception
     */
    public static String decrypt(String src, String privateKey) throws Exception {
        byte[] keyBytes = Base64.decodeBase64(privateKey);
        PKCS8EncodedKeySpec pkcs8KeySpec = new PKCS8EncodedKeySpec(keyBytes);
        KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);
        Key privateK = keyFactory.generatePrivate(pkcs8KeySpec);
        Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
        cipher.init(Cipher.DECRYPT_MODE, privateK);
        byte[] encryptedData = Base64.decodeBase64(src);
        int inputLen = encryptedData.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(encryptedData, offSet, MAX_DECRYPT_BLOCK);
            } else {
                cache = cipher.doFinal(encryptedData, offSet, inputLen - offSet);
            }
            out.write(cache, 0, cache.length);
            i++;
            offSet = i * MAX_DECRYPT_BLOCK;
        }
        byte[] decryptedData = out.toByteArray();
        out.close();
        return new String(decryptedData, CHARACTER_ENCODEING);
    }

    /**
     * <p>
     * 公钥加密
     * </p>
     * 
     * @param data
     *            源数据
     * @param publicKey公钥
     *            (hex编码)
     * @return
     * @throws Exception
     */
    public static String encryptByPublicKey(String src, String publicKey) throws Exception {
        byte[] keyBytes = Base64.decodeBase64(publicKey.getBytes("utf-8"));
        X509EncodedKeySpec x509KeySpec = new X509EncodedKeySpec(keyBytes);
        KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);
        Key publicK = keyFactory.generatePublic(x509KeySpec);
        // 对数据加密
        Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
        cipher.init(Cipher.ENCRYPT_MODE, publicK);
        byte[] data = src.getBytes(CHARACTER_ENCODEING);
        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) {
                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 Base64.encodeBase64URLSafeString(encryptedData);
    }

    /**
     * <p>
     * 获取私钥
     * </p>
     * 
     * @param keyMap密钥对
     * @return
     * @throws Exception
     */
    public static String getPrivateKey(Map<String, Object> keyMap) throws Exception {
        Key key = (Key) keyMap.get(PRIVATE_KEY);
        return Base64.encodeBase64URLSafeString(key.getEncoded());
    }

    /**
     * <p>
     * 获取公钥
     * </p>
     * 
     * @param keyMap密钥对
     * @return
     * @throws Exception
     */
    public static String getPublicKey(Map<String, Object> keyMap) throws Exception {
        Key key = (Key) keyMap.get(PUBLIC_KEY);
        return Base64.encodeBase64URLSafeString(key.getEncoded());
    }

    /**
     * 使用模和指数生成RSA公钥
     * 
     * @param modulus模
     * @param exponent指数
     * @return
     */
    public static RSAPublicKey getPublicKey(String modulus, String exponent) {
        try {
            BigInteger b1 = new BigInteger(modulus);
            BigInteger b2 = new BigInteger(exponent);
            KeyFactory keyFactory = KeyFactory.getInstance(SIGNATURE_ALGORITHM);
            RSAPublicKeySpec keySpec = new RSAPublicKeySpec(b1, b2);
            return (RSAPublicKey) keyFactory.generatePublic(keySpec);
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }

    /**
     * 使用模和指数生成RSA私钥
     * 
     * @param modulus模
     * @param exponent指数
     * @return
     */
    public static RSAPrivateKey getPrivateKey(String modulus, String exponent) {
        try {
            BigInteger b1 = new BigInteger(modulus);
            BigInteger b2 = new BigInteger(exponent);
            KeyFactory keyFactory = KeyFactory.getInstance(SIGNATURE_ALGORITHM);
            RSAPrivateKeySpec keySpec = new RSAPrivateKeySpec(b1, b2);
            return (RSAPrivateKey) keyFactory.generatePrivate(keySpec);
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }

    public static void main(String[] args) throws Exception {
        Map<String, Object> key = RSAUtil.genKeyPair();
        String publicKey = getPublicKey(key);
        String privateKey = getPrivateKey(key);
        String a = encryptByPublicKey("11213",getPublicKey(key));
 
        System.out.println(decrypt(a,getPrivateKey(key)));
        
        String  b = sign("1213", privateKey);
     
        System.out.println(verify("1213", publicKey, b));

    }
}

运行main函数 得出结果

11213true

从结果上可以看到  使用公钥对“11213”加密， 通过私钥解密得出加密前的数据；同理 用私钥对数据签名，再用公钥验证 数据是否正确 ，这里用了“1213”，如果验证的数据不是原始数据  会返回false

想多试其他情况  ，可以试试