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package org.springframework.security.crypto.encrypt;

import static org.springframework.security.crypto.encrypt.CipherUtils.doFinal;
import static org.springframework.security.crypto.encrypt.CipherUtils.initCipher;
import static org.springframework.security.crypto.encrypt.CipherUtils.newSecretKey;
import static org.springframework.security.crypto.util.EncodingUtils.concatenate;
import static org.springframework.security.crypto.util.EncodingUtils.subArray;

import javax.crypto.Cipher;
import javax.crypto.SecretKey;
import javax.crypto.spec.PBEKeySpec;
import javax.crypto.spec.SecretKeySpec;

import org.springframework.security.crypto.codec.Hex;
import org.springframework.security.crypto.encrypt.AesBytesEncryptor.CipherAlgorithm;
import org.springframework.security.crypto.keygen.BytesKeyGenerator;

/**
 * @see org.springframework.security.crypto.encrypt.AesBytesEncryptor
 * @see javax.crypto.SecretKeyFactory#getInstance(String)
 */
public class AesBytesEncryptorCustom implements BytesEncryptor {
  private final SecretKey secretKey;
  private final Cipher encryptor;
  private final Cipher decryptor;
  private final BytesKeyGenerator ivGenerator;
  private CipherAlgorithm alg;

  public AesBytesEncryptorCustom(String password, CharSequence salt, BytesKeyGenerator ivGenerator, CipherAlgorithm alg, int iterationCount, int keyLength, String algorithm) {
    PBEKeySpec keySpec = new PBEKeySpec(password.toCharArray(), Hex.decode(salt), iterationCount, keyLength);
    SecretKey secretKey = newSecretKey(algorithm, keySpec);
    this.secretKey = new SecretKeySpec(secretKey.getEncoded(), "AES");
    this.alg = alg;
    this.encryptor = alg.createCipher();
    this.decryptor = alg.createCipher();
    this.ivGenerator = ivGenerator != null ? ivGenerator : alg.defaultIvGenerator();
  }

  @Override
  public byte[] encrypt(byte[] bytes) {
    synchronized (this.encryptor) {
      byte[] iv = this.ivGenerator.generateKey();
      initCipher(this.encryptor, Cipher.ENCRYPT_MODE, this.secretKey, this.alg.getParameterSpec(iv));
      byte[] encrypted = doFinal(this.encryptor, bytes);
      return this.ivGenerator != NULL_IV_GENERATOR ? concatenate(iv, encrypted) : encrypted;
    }
  }

  @Override
  public byte[] decrypt(byte[] encryptedBytes) {
    synchronized (this.decryptor) {
      byte[] iv = iv(encryptedBytes);
      initCipher(this.decryptor, Cipher.DECRYPT_MODE, this.secretKey, this.alg.getParameterSpec(iv));
      return doFinal(this.decryptor, this.ivGenerator != NULL_IV_GENERATOR ? encrypted(encryptedBytes, iv.length) : encryptedBytes);
    }
  }

  // internal helpers
  private byte[] iv(byte[] encrypted) {
    return this.ivGenerator != NULL_IV_GENERATOR ? subArray(encrypted, 0, this.ivGenerator.getKeyLength()) : NULL_IV_GENERATOR.generateKey();
  }

  private byte[] encrypted(byte[] encryptedBytes, int ivLength) {
    return subArray(encryptedBytes, ivLength, encryptedBytes.length);
  }

  private static final BytesKeyGenerator NULL_IV_GENERATOR = new BytesKeyGenerator() {
    private final byte[] VALUE = new byte[16];

    @Override
    public int getKeyLength() {
      return this.VALUE.length;
    }

    @Override
    public byte[] generateKey() {
      return this.VALUE;
    }
  };
}