package seed.utils;

import java.security.MessageDigest;

import javax.crypto.Cipher;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;

public class nCertDecryptor {
	public static int BLOCK_SIZE = 16;

	public String decrypt(String secretKey, String iv, String cipher) throws Exception {

		// 암호화 알고리즘/모드/패딩
		String algorithm = "AES/CBC/PKCS5PADDING";

		// 비밀 키 디코딩
		byte[] decodedSecretKey = keyInstance(secretKey, BLOCK_SIZE);

		// 초기화 벡터 디코딩
		byte[] decodedIv = iv.getBytes("UTF-8");

		// 암호문 디코딩
		byte[] decodecCipher = nCertBase64.decode(cipher);

		// 복호화 객체 생성
		Cipher decipherInstance = Cipher.getInstance(algorithm);

		// 복호화 스펙 정의
		SecretKeySpec keySpec = new SecretKeySpec(decodedSecretKey, "AES");
		IvParameterSpec ivSpec = new IvParameterSpec(decodedIv);

		// 복호화 객체 초기화
		decipherInstance.init(Cipher.DECRYPT_MODE, keySpec, ivSpec);

		// 복호화
		byte[] plain = decipherInstance.doFinal(decodecCipher);

		// 복호화 된 평문(byte[])을 문자로 변환 
		return new String(plain, "UTF-8");

	}

	public byte[] keyInstance(String secretkey, int size) {
		
		byte[] retHashValue = new byte[size];

		try {
			MessageDigest md = MessageDigest.getInstance("SHA1");
			byte[] hash = md.digest(secretkey.getBytes("UTF-8"));
			size = Math.min(size, hash.length);
			System.arraycopy(hash, 0, retHashValue, 0, size);
		}catch(Exception e) {
			e.printStackTrace();
		}
		
		return retHashValue;
	}
}