/**
 * 
 */
package com.github.ibole.infrastructure.security;

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.SecureRandom;
import java.security.Signature;
import java.security.interfaces.DSAPrivateKey;
import java.security.interfaces.DSAPublicKey;
import java.security.spec.PKCS8EncodedKeySpec;
import java.security.spec.X509EncodedKeySpec;
import java.util.HashMap;
import java.util.Map;

/*********************************************************************************************.
 * 
 * 
 * <p>Copyright 2016, iBole Inc. All rights reserved.
 * 
 * <p></p>
 *********************************************************************************************/


/**
 * @author bwang (chikaiwang@hotmail.com)
 *
 */
public class DSACoder extends Coder {

  public static final String ALGORITHM = "DSA";

  /**
   * 默认密钥字节数.
   * 
   * <pre>
   * DSA 
   * Default Keysize 1024  
   * Keysize must be a multiple of 64, ranging from 512 to 1024 (inclusive).
   * </pre>
   */
  private static final int KEY_SIZE = 1024;

  /**
   * 默认种子
   */
  private static final String DEFAULT_SEED = "0f22507a10bbddd07d8a3082122966e3";

  private static final String PUBLIC_KEY = "DSAPublicKey";
  private static final String PRIVATE_KEY = "DSAPrivateKey";

  /**
   * 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, String privateKey) throws Exception {
      // 解密由base64编码的私钥
      byte[] keyBytes = decryptBASE64(privateKey);

      // 构造PKCS8EncodedKeySpec对象
      PKCS8EncodedKeySpec pkcs8KeySpec = new PKCS8EncodedKeySpec(keyBytes);

      // KEY_ALGORITHM 指定的加密算法
      KeyFactory keyFactory = KeyFactory.getInstance(ALGORITHM);

      // 取私钥匙对象
      PrivateKey priKey = keyFactory.generatePrivate(pkcs8KeySpec);

      // 用私钥对信息生成数字签名
      Signature signature = Signature.getInstance(keyFactory.getAlgorithm());
      signature.initSign(priKey);
      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, String publicKey, String sign)
          throws Exception {

      // 解密由base64编码的公钥
      byte[] keyBytes = decryptBASE64(publicKey);

      // 构造X509EncodedKeySpec对象
      X509EncodedKeySpec keySpec = new X509EncodedKeySpec(keyBytes);

      // ALGORITHM 指定的加密算法
      KeyFactory keyFactory = KeyFactory.getInstance(ALGORITHM);

      // 取公钥匙对象
      PublicKey pubKey = keyFactory.generatePublic(keySpec);

      Signature signature = Signature.getInstance(keyFactory.getAlgorithm());
      signature.initVerify(pubKey);
      signature.update(data);

      // 验证签名是否正常
      return signature.verify(decryptBASE64(sign));
  }

  /**
   * 生成密钥.
   * 
   * @param seed
   *            种子
   * @return 密钥对象
   * @throws Exception
   */
  public static Map<String, Object> initKey(String seed) throws Exception {
      KeyPairGenerator keygen = KeyPairGenerator.getInstance(ALGORITHM);
      // 初始化随机产生器
      SecureRandom secureRandom = new SecureRandom();
      secureRandom.setSeed(seed.getBytes());
      keygen.initialize(KEY_SIZE, secureRandom);

      KeyPair keys = keygen.genKeyPair();

      DSAPublicKey publicKey = (DSAPublicKey) keys.getPublic();
      DSAPrivateKey privateKey = (DSAPrivateKey) keys.getPrivate();

      Map<String, Object> map = new HashMap<String, Object>(2);
      map.put(PUBLIC_KEY, publicKey);
      map.put(PRIVATE_KEY, privateKey);

      return map;
  }

  /**
   * 默认生成密钥.
   * 
   * @return 密钥对象
   * @throws Exception
   */
  public static Map<String, Object> initKey() throws Exception {
      return initKey(DEFAULT_SEED);
  }

  /**
   * 取得私钥.
   * 
   * @param keyMap
   * @return
   * @throws Exception
   */
  public static String getPrivateKey(Map<String, Object> keyMap)
          throws Exception {
      Key key = (Key) keyMap.get(PRIVATE_KEY);

      return encryptBASE64(key.getEncoded());
  }

  /**
   * 取得公钥.
   * 
   * @param keyMap
   * @return
   * @throws Exception
   */
  public static String getPublicKey(Map<String, Object> keyMap)
          throws Exception {
      Key key = (Key) keyMap.get(PUBLIC_KEY);

      return encryptBASE64(key.getEncoded());
  }
}
