JceKeyCipher.java

/*
 * Copyright 2019 Amazon.com, Inc. or its affiliates. All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License"). You may not use this file except
 * in compliance with the License. A copy of the License is located at
 *
 * http://aws.amazon.com/apache2.0
 *
 * or in the "license" file accompanying this file. This file 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.amazonaws.encryptionsdk.internal;

import com.amazonaws.encryptionsdk.EncryptedDataKey;
import com.amazonaws.encryptionsdk.exception.AwsCryptoException;
import com.amazonaws.encryptionsdk.model.KeyBlob;
import org.apache.commons.lang3.ArrayUtils;

import javax.crypto.Cipher;
import javax.crypto.SecretKey;
import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;
import java.security.GeneralSecurityException;
import java.security.Key;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.util.Map;

/**
 * Abstract class for encrypting and decrypting JCE data keys.
 */
public abstract class JceKeyCipher {

    private final Key wrappingKey;
    private final Key unwrappingKey;
    private static final Charset KEY_NAME_ENCODING = StandardCharsets.UTF_8;

    /**
     * Returns a new instance of a JceKeyCipher based on the
     * Advanced Encryption Standard in Galois/Counter Mode.
     *
     * @param secretKey The secret key to use for encrypt/decrypt operations.
     * @return The JceKeyCipher.
     */
    public static JceKeyCipher aesGcm(SecretKey secretKey) {
        return new AesGcmJceKeyCipher(secretKey);
    }

    /**
     * Returns a new instance of a JceKeyCipher based on RSA.
     *
     * @param wrappingKey The public key to use for encrypting the key.
     * @param unwrappingKey The private key to use for decrypting the key.
     * @param transformation The transformation.
     * @return The JceKeyCipher.
     */
    public static JceKeyCipher rsa(PublicKey wrappingKey, PrivateKey unwrappingKey, String transformation) {
        return new RsaJceKeyCipher(wrappingKey, unwrappingKey, transformation);
    }

    JceKeyCipher(Key wrappingKey, Key unwrappingKey) {
        this.wrappingKey = wrappingKey;
        this.unwrappingKey = unwrappingKey;
    }

    abstract WrappingData buildWrappingCipher(Key key, Map<String, String> encryptionContext) throws GeneralSecurityException;

    abstract Cipher buildUnwrappingCipher(Key key, byte[] extraInfo, int offset,
                                          Map<String, String> encryptionContext) throws GeneralSecurityException;


    /**
     * Encrypts the given key, incorporating the given keyName and encryptionContext.
     * @param key The key to encrypt.
     * @param keyName A UTF-8 encoded representing a name for the key.
     * @param keyNamespace A UTF-8 encoded value that namespaces the key.
     * @param encryptionContext A key-value mapping of arbitrary, non-secret, UTF-8 encoded strings used
     *                         during encryption and decryption to provide additional authenticated data (AAD).
     * @return The encrypted data key.
     */
    public EncryptedDataKey encryptKey(final byte[] key, final String keyName, final String keyNamespace,
                                       final Map<String, String> encryptionContext) {

        final byte[] keyNameBytes = keyName.getBytes(KEY_NAME_ENCODING);

        try {
            final JceKeyCipher.WrappingData wData = buildWrappingCipher(wrappingKey, encryptionContext);
            final Cipher cipher = wData.cipher;
            final byte[] encryptedKey = cipher.doFinal(key);

            final byte[] provInfo;
            if (wData.extraInfo.length == 0) {
                provInfo = keyNameBytes;
            } else {
                provInfo = new byte[keyNameBytes.length + wData.extraInfo.length];
                System.arraycopy(keyNameBytes, 0, provInfo, 0, keyNameBytes.length);
                System.arraycopy(wData.extraInfo, 0, provInfo, keyNameBytes.length, wData.extraInfo.length);
            }

            return new KeyBlob(keyNamespace, provInfo, encryptedKey);
        } catch (final GeneralSecurityException gsex) {
            throw new AwsCryptoException(gsex);
        }
    }

    /**
     * Decrypts the given encrypted data key.
     *
     * @param edk The encrypted data key.
     * @param keyName A UTF-8 encoded String representing a name for the key.
     * @param encryptionContext A key-value mapping of arbitrary, non-secret, UTF-8 encoded strings used
     *                          during encryption and decryption to provide additional authenticated data (AAD).
     * @return The decrypted key.
     * @throws GeneralSecurityException If a problem occurred decrypting the key.
     */
    public byte[] decryptKey(final EncryptedDataKey edk, final String keyName,
                              final Map<String, String> encryptionContext) throws GeneralSecurityException {
        final byte[] keyNameBytes = keyName.getBytes(KEY_NAME_ENCODING);

        final Cipher cipher = buildUnwrappingCipher(unwrappingKey, edk.getProviderInformation(),
                keyNameBytes.length, encryptionContext);
        return cipher.doFinal(edk.getEncryptedDataKey());
    }

    static class WrappingData {
        public final Cipher cipher;
        public final byte[] extraInfo;

        WrappingData(final Cipher cipher, final byte[] extraInfo) {
            this.cipher = cipher;
            this.extraInfo = extraInfo != null ? extraInfo : ArrayUtils.EMPTY_BYTE_ARRAY;
        }
    }
}