/**
* Encryptor.java
* Copyright 2008 Zach Scrivena
* zachscrivena@gmail.com
* http://zs.freeshell.org/
*
* TERMS AND CONDITIONS:
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
package org.freeshell.zs.common;
import java.security.MessageDigest;
import java.security.SecureRandom;
import java.util.Arrays;
import javax.crypto.Cipher;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;
/**
* Perform AES-128 encryption.
*/
public final class Encryptor
{
/** name of the character set to use for converting between characters and bytes */
private static final String CHARSET_NAME = "UTF-8";
/** random number generator algorithm */
private static final String RNG_ALGORITHM = "SHA1PRNG";
/** message digest algorithm (must be sufficiently long to provide the key and initialization vector) */
private static final String DIGEST_ALGORITHM = "SHA-256";
/** key algorithm (must be compatible with CIPHER_ALGORITHM) */
private static final String KEY_ALGORITHM = "AES";
/** cipher algorithm (must be compatible with KEY_ALGORITHM) */
private static final String CIPHER_ALGORITHM = "AES/CBC/PKCS5Padding";
/**
* Private constructor that should never be called.
*/
private Encryptor()
{}
/**
* Encrypt the specified cleartext using the given password.
* With the correct salt, number of iterations, and password, the decrypt() method reverses
* the effect of this method.
* This method generates and uses a random salt, and the user-specified number of iterations
* and password to create a 16-byte secret key and 16-byte initialization vector.
* The secret key and initialization vector are then used in the AES-128 cipher to encrypt
* the given cleartext.
*
* @param salt
* salt that was used in the encryption (to be populated)
* @param iterations
* number of iterations to use in salting
* @param password
* password to be used for encryption
* @param cleartext
* cleartext to be encrypted
* @return
* ciphertext
* @throws Exception
* on any error encountered in encryption
*/
public static byte[] encrypt(
final byte[] salt,
final int iterations,
final String password,
final byte[] cleartext)
throws Exception
{
/* generate salt randomly */
SecureRandom.getInstance(RNG_ALGORITHM).nextBytes(salt);
/* compute key and initialization vector */
final MessageDigest shaDigest = MessageDigest.getInstance(DIGEST_ALGORITHM);
byte[] pw = password.getBytes(CHARSET_NAME);
for (int i = 0; i < iterations; i++)
{
/* add salt */
final byte[] salted = new byte[pw.length + salt.length];
System.arraycopy(pw, 0, salted, 0, pw.length);
System.arraycopy(salt, 0, salted, pw.length, salt.length);
Arrays.fill(pw, (byte) 0x00);
/* compute SHA-256 digest */
shaDigest.reset();
pw = shaDigest.digest(salted);
Arrays.fill(salted, (byte) 0x00);
}
/* extract the 16-byte key and initialization vector from the SHA-256 digest */
final byte[] key = new byte[16];
final byte[] iv = new byte[16];
System.arraycopy(pw, 0, key, 0, 16);
System.arraycopy(pw, 16, iv, 0, 16);
Arrays.fill(pw, (byte) 0x00);
/* perform AES-128 encryption */
final Cipher cipher = Cipher.getInstance(CIPHER_ALGORITHM);
cipher.init(
Cipher.ENCRYPT_MODE,
new SecretKeySpec(key, KEY_ALGORITHM),
new IvParameterSpec(iv));
Arrays.fill(key, (byte) 0x00);
Arrays.fill(iv, (byte) 0x00);
return cipher.doFinal(cleartext);
}
/**
* Decrypt the specified ciphertext using the given password.
* With the correct salt, number of iterations, and password, this method reverses the effect
* of the encrypt() method.
* This method uses the user-specified salt, number of iterations, and password
* to recreate the 16-byte secret key and 16-byte initialization vector.
* The secret key and initialization vector are then used in the AES-128 cipher to decrypt
* the given ciphertext.
*
* @param salt
* salt to be used in decryption
* @param iterations
* number of iterations to use in salting
* @param password
* password to be used for decryption
* @param ciphertext
* ciphertext to be decrypted
* @return
* cleartext
* @throws Exception
* on any error encountered in decryption
*/
public static byte[] decrypt(
final byte[] salt,
final int iterations,
final String password,
final byte[] ciphertext)
throws Exception
{
/* compute key and initialization vector */
final MessageDigest shaDigest = MessageDigest.getInstance(DIGEST_ALGORITHM);
byte[] pw = password.getBytes(CHARSET_NAME);
for (int i = 0; i < iterations; i++)
{
/* add salt */
final byte[] salted = new byte[pw.length + salt.length];
System.arraycopy(pw, 0, salted, 0, pw.length);
System.arraycopy(salt, 0, salted, pw.length, salt.length);
Arrays.fill(pw, (byte) 0x00);
/* compute SHA-256 digest */
shaDigest.reset();
pw = shaDigest.digest(salted);
Arrays.fill(salted, (byte) 0x00);
}
/* extract the 16-byte key and initialization vector from the SHA-256 digest */
final byte[] key = new byte[16];
final byte[] iv = new byte[16];
System.arraycopy(pw, 0, key, 0, 16);
System.arraycopy(pw, 16, iv, 0, 16);
Arrays.fill(pw, (byte) 0x00);
/* perform AES-128 decryption */
final Cipher cipher = Cipher.getInstance(CIPHER_ALGORITHM);
cipher.init(
Cipher.DECRYPT_MODE,
new SecretKeySpec(key, KEY_ALGORITHM),
new IvParameterSpec(iv));
Arrays.fill(key, (byte) 0x00);
Arrays.fill(iv, (byte) 0x00);
return cipher.doFinal(ciphertext);
}
}