Java tutorial
/** * Copyright 2013 Jim Burton. * * Licensed under the MIT license (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://opensource.org/licenses/mit-license.php * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package com.google.bitcoin.crypto; import com.google.protobuf.ByteString; import com.lambdaworks.crypto.SCrypt; import org.bitcoinj.wallet.Protos; import org.bitcoinj.wallet.Protos.ScryptParameters; import org.bitcoinj.wallet.Protos.Wallet.EncryptionType; import org.slf4j.Logger; import org.slf4j.LoggerFactory; import org.bouncycastle.crypto.BufferedBlockCipher; import org.bouncycastle.crypto.engines.AESFastEngine; import org.bouncycastle.crypto.modes.CBCBlockCipher; import org.bouncycastle.crypto.paddings.PaddedBufferedBlockCipher; import org.bouncycastle.crypto.params.KeyParameter; import org.bouncycastle.crypto.params.ParametersWithIV; import java.io.Serializable; import java.security.SecureRandom; import java.util.Arrays; import static com.google.common.base.Preconditions.checkNotNull; /** * <p>This class encrypts and decrypts byte arrays and strings using scrypt as the * key derivation function and AES for the encryption.</p> * * <p>You can use this class to:</p> * * <p>1) Using a user password, create an AES key that can encrypt and decrypt your private keys. * To convert the password to the AES key, scrypt is used. This is an algorithm resistant * to brute force attacks. You can use the ScryptParameters to tune how difficult you * want this to be generation to be.</p> * * <p>2) Using the AES Key generated above, you then can encrypt and decrypt any bytes using * the AES symmetric cipher. Eight bytes of salt is used to prevent dictionary attacks.</p> */ public class KeyCrypterScrypt implements KeyCrypter, Serializable { private static final Logger log = LoggerFactory.getLogger(KeyCrypterScrypt.class); private static final long serialVersionUID = 949662512049152670L; /** * Key length in bytes. */ public static final int KEY_LENGTH = 32; // = 256 bits. /** * The size of an AES block in bytes. * This is also the length of the initialisation vector. */ public static final int BLOCK_LENGTH = 16; // = 128 bits. /** * The length of the salt used. */ public static final int SALT_LENGTH = 8; private static final transient SecureRandom secureRandom = new SecureRandom(); // Scrypt parameters. private final transient ScryptParameters scryptParameters; /** * Encryption/ Decryption using default parameters and a random salt */ public KeyCrypterScrypt() { byte[] salt = new byte[SALT_LENGTH]; secureRandom.nextBytes(salt); Protos.ScryptParameters.Builder scryptParametersBuilder = Protos.ScryptParameters.newBuilder() .setSalt(ByteString.copyFrom(salt)); this.scryptParameters = scryptParametersBuilder.build(); } /** * Encryption/ Decryption using specified Scrypt parameters. * * @param scryptParameters ScryptParameters to use * @throws NullPointerException if the scryptParameters or any of its N, R or P is null. */ public KeyCrypterScrypt(ScryptParameters scryptParameters) { this.scryptParameters = checkNotNull(scryptParameters); // Check there is a non-empty salt. // (Some early MultiBit wallets has a missing salt so it is not a hard fail). if (scryptParameters.getSalt() == null || scryptParameters.getSalt().toByteArray() == null || scryptParameters.getSalt().toByteArray().length == 0) { log.warn( "You are using a ScryptParameters with no salt. Your encryption may be vulnerable to a dictionary attack."); } } /** * Generate AES key. * * This is a very slow operation compared to encrypt/ decrypt so it is normally worth caching the result. * * @param password The password to use in key generation * @return The KeyParameter containing the created AES key * @throws KeyCrypterException */ @Override public KeyParameter deriveKey(CharSequence password) throws KeyCrypterException { byte[] passwordBytes = null; try { passwordBytes = convertToByteArray(password); byte[] salt = new byte[0]; if (scryptParameters.getSalt() != null) { salt = scryptParameters.getSalt().toByteArray(); } else { // Warn the user that they are not using a salt. // (Some early MultiBit wallets had a blank salt). log.warn( "You are using a ScryptParameters with no salt. Your encryption may be vulnerable to a dictionary attack."); } byte[] keyBytes = SCrypt.scrypt(passwordBytes, salt, (int) scryptParameters.getN(), scryptParameters.getR(), scryptParameters.getP(), KEY_LENGTH); return new KeyParameter(keyBytes); } catch (Exception e) { throw new KeyCrypterException("Could not generate key from password and salt.", e); } finally { // Zero the password bytes. if (passwordBytes != null) { java.util.Arrays.fill(passwordBytes, (byte) 0); } } } /** * Password based encryption using AES - CBC 256 bits. */ @Override public EncryptedPrivateKey encrypt(byte[] plainBytes, KeyParameter aesKey) throws KeyCrypterException { checkNotNull(plainBytes); checkNotNull(aesKey); try { // Generate iv - each encryption call has a different iv. byte[] iv = new byte[BLOCK_LENGTH]; secureRandom.nextBytes(iv); ParametersWithIV keyWithIv = new ParametersWithIV(aesKey, iv); // Encrypt using AES. BufferedBlockCipher cipher = new PaddedBufferedBlockCipher(new CBCBlockCipher(new AESFastEngine())); cipher.init(true, keyWithIv); byte[] encryptedBytes = new byte[cipher.getOutputSize(plainBytes.length)]; final int length1 = cipher.processBytes(plainBytes, 0, plainBytes.length, encryptedBytes, 0); final int length2 = cipher.doFinal(encryptedBytes, length1); return new EncryptedPrivateKey(iv, Arrays.copyOf(encryptedBytes, length1 + length2)); } catch (Exception e) { throw new KeyCrypterException("Could not encrypt bytes.", e); } } /** * Decrypt bytes previously encrypted with this class. * * @param privateKeyToDecode The private key to decrypt * @param aesKey The AES key to use for decryption * @return The decrypted bytes * @throws KeyCrypterException if bytes could not be decoded to a valid key */ @Override public byte[] decrypt(EncryptedPrivateKey privateKeyToDecode, KeyParameter aesKey) throws KeyCrypterException { checkNotNull(privateKeyToDecode); checkNotNull(aesKey); try { ParametersWithIV keyWithIv = new ParametersWithIV(new KeyParameter(aesKey.getKey()), privateKeyToDecode.getInitialisationVector()); // Decrypt the message. BufferedBlockCipher cipher = new PaddedBufferedBlockCipher(new CBCBlockCipher(new AESFastEngine())); cipher.init(false, keyWithIv); byte[] cipherBytes = privateKeyToDecode.getEncryptedBytes(); byte[] decryptedBytes = new byte[cipher.getOutputSize(cipherBytes.length)]; final int length1 = cipher.processBytes(cipherBytes, 0, cipherBytes.length, decryptedBytes, 0); final int length2 = cipher.doFinal(decryptedBytes, length1); return Arrays.copyOf(decryptedBytes, length1 + length2); } catch (Exception e) { throw new KeyCrypterException("Could not decrypt bytes", e); } } /** * Convert a CharSequence (which are UTF16) into a byte array. * * Note: a String.getBytes() is not used to avoid creating a String of the password in the JVM. */ private static byte[] convertToByteArray(CharSequence charSequence) { checkNotNull(charSequence); byte[] byteArray = new byte[charSequence.length() << 1]; for (int i = 0; i < charSequence.length(); i++) { int bytePosition = i << 1; byteArray[bytePosition] = (byte) ((charSequence.charAt(i) & 0xFF00) >> 8); byteArray[bytePosition + 1] = (byte) (charSequence.charAt(i) & 0x00FF); } return byteArray; } public ScryptParameters getScryptParameters() { return scryptParameters; } /** * Return the EncryptionType enum value which denotes the type of encryption/ decryption that this KeyCrypter * can understand. */ @Override public EncryptionType getUnderstoodEncryptionType() { return EncryptionType.ENCRYPTED_SCRYPT_AES; } @Override public String toString() { return "Scrypt/AES"; } @Override public int hashCode() { return com.google.common.base.Objects.hashCode(scryptParameters); } @Override public boolean equals(Object obj) { if (obj == null) { return false; } if (getClass() != obj.getClass()) { return false; } final KeyCrypterScrypt other = (KeyCrypterScrypt) obj; return com.google.common.base.Objects.equal(this.scryptParameters, other.scryptParameters); } }