package com.idea.util;

import javax.crypto.Cipher;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import java.nio.charset.StandardCharsets;
import java.security.MessageDigest;
import java.util.Base64;

public class AESUtil {
    public static String decryptKey(String tokenId, String pw) throws Exception {

// MD5加密

        byte[] md5Byte =MessageDigest.getInstance("MD5").digest(tokenId.getBytes());

// 转为16进制字符串

        String hexStr = bytesToHex(md5Byte);

// 截取

        String aesKey = hexStr.substring(8, 24);

// AES解密，返回结果

        return decrypt(pw, aesKey, aesKey);

    }

    private static String bytesToHex(byte[] bytes) {

        StringBuilder sb = new StringBuilder(bytes.length * 2);

        for (int i = 0; i < bytes.length; i++) {

            sb.append(Character.toUpperCase(Character.forDigit((bytes[i] >> 4) & 0x0F, 16)));

            sb.append(Character.toUpperCase(Character.forDigit(bytes[i] & 0x0F, 16)));

        }

        return sb.toString();

    }

    private static String decrypt(String pw, String aesKey, String viPara) throws Exception {

        IvParameterSpec zeroIv = new IvParameterSpec(viPara.getBytes());

        SecretKeySpec key = new SecretKeySpec(aesKey.getBytes(), "AES");

        Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");

        cipher.init(Cipher.DECRYPT_MODE, key, zeroIv);

        return new String(cipher.doFinal(Base64.getDecoder().decode(pw)), StandardCharsets.UTF_8);

    }

}