java 使用pem密钥进行RSA加解密

1.使用openssl生成私钥和公钥

openssl下载地址：http://www.openssl.org/source

openssl生成私钥命令： genrsa -out rsa_private_key.pem 1024

openssl生成公钥命令： rsa -in rsa_private_key.pem -pubout -out rsa_public_key.pem

2.此时在openssl安装目录下的bin文件夹可以看到 rsa_private_key.pem 和 rsa_public_key.pem 两个文件。这时候的私钥是不能直接使用的，需要进行 pkcs8 编码

openssl的pkcs8编码命令：pkcs8 -topk8 -in rsa_private_key.pem -out pkcs8_rsa_private_key.pem -nocrypt

那么在bin文件夹可以看到 pkcs8_rsa_private_key.pem 文件。至此，可用的密钥对已经生成好了，私钥使用pkcs8_rsa_private_key.pem，公钥采用rsa_public_key.pem。

3.使用密钥对进行签名、加解密

public class RSAPemCoder {
    public static final String KEY_SHA = "SHA";   
    public static final String KEY_MD5 = "MD5";
    public static final String KEY_ALGORITHM = "RSA";
    public static final String SIGNATURE_ALGORITHM = "MD5withRSA";

    /**
     * 用私钥对信息生成数字签名
     *
     * @param data 加密数据
     * @param privateKey 私钥
     * @return
     * @throws Exception
     */
    public static String sign(byte[] data, PrivateKey privateKey) throws Exception {  
        Signature signature = Signature.getInstance(SIGNATURE_ALGORITHM);
        signature.initSign(privateKey);
        signature.update(data);
        return encryptBASE64(signature.sign());
    }

    /**
     * 校验数字签名
     *
     * @param data 加密数据
     * @param publicKey 公钥
     * @param sign 数字签名
     * @return 校验成功返回true 失败返回false
     * @throws Exception
     */
    public static boolean verify(byte[] data, PublicKey publicKey, String sign) throws Exception {
        Signature signature = Signature.getInstance(SIGNATURE_ALGORITHM);
        signature.initVerify(publicKey);
        signature.update(data);
        return signature.verify(decryptBASE64(sign));
    }

    /**
     * 私钥解密
     *
     * @param data 密文
     * @param PrivateKey 私钥
     * @return
     * @throws Exception
     */
    public static byte[] decryptByPrivateKey(byte[] data, PrivateKey privateKey) throws Exception {
        KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);
        Cipher cipher = Cipher.getInstance(keyFactory.getAlgorithm());
        cipher.init(Cipher.DECRYPT_MODE, privateKey);
        return cipher.doFinal(data);
    }

    /**
     * 用公钥解密
     *
     * @param data 密文
     * @param publicKey 公钥 
     * @return
     * @throws Exception
     */
    public static byte[] decryptByPublicKey(byte[] data, PublicKey publicKey) throws Exception {
        KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);
        Cipher cipher = Cipher.getInstance(keyFactory.getAlgorithm());
        cipher.init(Cipher.DECRYPT_MODE, publicKey);
        return cipher.doFinal(data);
    }

    /**
     * 用公钥加密
     *
     * @param data 明文
     * @param PublicKey 公钥
     * @return
     * @throws Exception
     */
    public static byte[] encryptByPublicKey(byte[] data, PublicKey publicKey) throws Exception {
        KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);
        Cipher cipher = Cipher.getInstance(keyFactory.getAlgorithm());
        cipher.init(Cipher.ENCRYPT_MODE, publicKey);
        return cipher.doFinal(data);
    }

    /**
     * 用私钥加密
     *
     * @param data 明文
     * @param privateKey 私钥
     * @return
     * @throws Exception
     */
    public static byte[] encryptByPrivateKey(byte[] data, PrivateKey privateKey) throws Exception {
        KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);
        Cipher cipher = Cipher.getInstance(keyFactory.getAlgorithm());
        cipher.init(Cipher.ENCRYPT_MODE, privateKey);
        return cipher.doFinal(data);
    }

    public static PrivateKey getPrivateKeyFromPem() throws Exception {
        BufferedReader br = new BufferedReader(new FileReader("e:/pkcs8_privatekey.pem"));
        String s = br.readLine();
        String str = "";
        s = br.readLine();
        while (s.charAt(0) != '-') {
            str += s + "\r";
            s = br.readLine();
        }
        BASE64Decoder base64decoder = new BASE64Decoder();
        byte[] b = base64decoder.decodeBuffer(str);

        // 生成私匙  
        KeyFactory kf = KeyFactory.getInstance("RSA");
        PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(b);
        PrivateKey privateKey = kf.generatePrivate(keySpec);
        return privateKey;
    }

    public static PublicKey getPublicKeyFromPem() throws Exception {
        BufferedReader br = new BufferedReader(new FileReader("e:/publickey.pem"));
        String s = br.readLine();
        String str = "";
        s = br.readLine();
        while (s.charAt(0) != '-') {
            str += s + "\r";
            s = br.readLine();
        }
        BASE64Decoder base64decoder = new BASE64Decoder();
        byte[] b = base64decoder.decodeBuffer(str);
        KeyFactory kf = KeyFactory.getInstance("RSA");
        X509EncodedKeySpec keySpec = new X509EncodedKeySpec(b);
        PublicKey pubKey = kf.generatePublic(keySpec);
        return pubKey;
    }
    
    public static byte[] decryptBASE64(String key) throws Exception {   
        return (new BASE64Decoder()).decodeBuffer(key);   
    }   
  
    public static String encryptBASE64(byte[] key) throws Exception {   
        return (new BASE64Encoder()).encodeBuffer(key);   
    }   

    public static byte[] encryptMD5(byte[] data) throws Exception {   
  
        MessageDigest md5 = MessageDigest.getInstance(KEY_MD5);   
        md5.update(data);   
  
        return md5.digest();   
  
    }   
  
    public static byte[] encryptSHA(byte[] data) throws Exception {   
  
        MessageDigest sha = MessageDigest.getInstance(KEY_SHA);   
        sha.update(data);   
  
        return sha.digest();   
  
    }   
}