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package encryptiontest;

import java.io.UnsupportedEncodingException;
import java.math.BigInteger;
import java.nio.charset.Charset;
import java.security.GeneralSecurityException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
import java.util.Arrays;
import java.util.Base64;
import javax.crypto.Cipher;
import javax.crypto.spec.SecretKeySpec;

public class EncryptionTest {

  private static final SecureRandom random = new SecureRandom();

  public static String nextSessionId() {
    return new BigInteger(130, random).toString(63);
  }

    public static void main(String[] args) throws UnsupportedEncodingException, GeneralSecurityException, Exception {
        while(true) {
            String key = nextSessionId();
            String source = nextSessionId();
            String result = encrypt(getKey(key), source);

            System.out.println("source = " + source);
            System.out.println("key = " + key);
            System.out.println("result = " + result);

            result = decrypt(getKey(key), result);

            if (result.equals(source)) {
            } else {
                throw new Exception("Fail");
            }
        }
    }

    private static String encrypt(byte[] key, String value) throws GeneralSecurityException {
        // Argument validation.
        if (key.length != 16) {
            throw new IllegalArgumentException("Invalid key size.");
        }

        // Setup AES tool.
        SecretKeySpec secretKeySpec = new SecretKeySpec(key, "AES");
        Cipher cipher = Cipher.getInstance("AES");
        cipher.init(Cipher.ENCRYPT_MODE, secretKeySpec);

        // Do the job with AES tool.
        byte[] original = value.getBytes(Charset.forName("UTF-8"));
        byte[] binary = cipher.doFinal(original);
        return Base64.getEncoder().encodeToString(binary);
    }

    private static String decrypt(byte[] key, String encrypted) throws GeneralSecurityException {
        // Argument validation.
        if (key.length != 16) {
            throw new IllegalArgumentException("Invalid key size.");
        }

        // Setup AES tool.
        SecretKeySpec secretKeySpec = new SecretKeySpec(key, "AES");
        Cipher cipher = Cipher.getInstance("AES");
        cipher.init(Cipher.DECRYPT_MODE, secretKeySpec);

        // Do the job with AES tool.
        byte[] binary = Base64.getDecoder().decode(encrypted);
        byte[] original = cipher.doFinal(binary);
        return new String(original, Charset.forName("UTF-8"));
    }

    private static byte[] getKey(String string) throws UnsupportedEncodingException, NoSuchAlgorithmException {
        MessageDigest sha = MessageDigest.getInstance("SHA-1");
        byte[] key = sha.digest(string.getBytes("UTF-8"));
        key = Arrays.copyOf(key, 16);
        return key;
    }
}