/*
 * nimbus-jose-jwt
 *
 * Copyright 2012-2016, Connect2id Ltd.
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use
 * this file except in compliance with the License. You may obtain a copy of the
 * License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * 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.nimbusds.jose.crypto;


import java.util.Set;
import javax.crypto.SecretKey;
import javax.crypto.spec.SecretKeySpec;

import net.jcip.annotations.ThreadSafe;

import com.nimbusds.jose.*;
import com.nimbusds.jose.jwk.OctetSequenceKey;
import com.nimbusds.jose.util.Base64URL;


/**
 * Direct decrypter of {@link com.nimbusds.jose.JWEObject JWE objects} with a
 * shared symmetric key.
 *
 * <p>See RFC 7518
 * <a href="https://tools.ietf.org/html/rfc7518#section-4.5">section 4.5</a>
 * for more information.</p>
 *
 * <p>This class is thread-safe.
 *
 * <p>Supports the following key management algorithms:
 *
 * <ul>
 *     <li>{@link com.nimbusds.jose.JWEAlgorithm#DIR}
 * </ul>
 *
 * <p>Supports the following content encryption algorithms:
 *
 * <ul>
 *     <li>{@link com.nimbusds.jose.EncryptionMethod#A128CBC_HS256} (requires 256 bit key)
 *     <li>{@link com.nimbusds.jose.EncryptionMethod#A192CBC_HS384} (requires 384 bit key)
 *     <li>{@link com.nimbusds.jose.EncryptionMethod#A256CBC_HS512} (requires 512 bit key)
 *     <li>{@link com.nimbusds.jose.EncryptionMethod#A128GCM} (requires 128 bit key)
 *     <li>{@link com.nimbusds.jose.EncryptionMethod#A192GCM} (requires 192 bit key)
 *     <li>{@link com.nimbusds.jose.EncryptionMethod#A256GCM} (requires 256 bit key)
 *     <li>{@link com.nimbusds.jose.EncryptionMethod#A128CBC_HS256_DEPRECATED} (requires 256 bit key)
 *     <li>{@link com.nimbusds.jose.EncryptionMethod#A256CBC_HS512_DEPRECATED} (requires 512 bit key)
 * </ul>
 * 
 * @author Vladimir Dzhuvinov
 * @version 2015-06-29
 */
@ThreadSafe
public class DirectDecrypter extends DirectCryptoProvider implements JWEDecrypter, CriticalHeaderParamsAware {


        /**
         * The critical header policy.
         */
        private final CriticalHeaderParamsDeferral critPolicy = new CriticalHeaderParamsDeferral();


        /**
         * Creates a new direct decrypter.
         *
         * @param key The symmetric key. Its algorithm must be "AES". Must be
         *            128 bits (16 bytes), 192 bits (24 bytes), 256 bits (32
         *            bytes), 384 bits (48 bytes) or 512 bits (64 bytes) long.
         *            Must not be {@code null}.
         *
         * @throws KeyLengthException If the symmetric key length is not
         *                            compatible.
         */
        public DirectDecrypter(final SecretKey key)
                throws KeyLengthException {

                super(key);
        }


        /**
         * Creates a new direct decrypter.
         *
         * @param keyBytes The symmetric key, as a byte array. Must be 128 bits
         *                 (16 bytes), 192 bits (24 bytes), 256 bits (32
         *                 bytes), 384 bits (48 bytes) or 512 bits (64 bytes)
         *                 long. Must not be {@code null}.
         *
         * @throws KeyLengthException If the symmetric key length is not
         *                            compatible.
         */
        public DirectDecrypter(final byte[] keyBytes)
                throws KeyLengthException {

                this(new SecretKeySpec(keyBytes, "AES"));
        }


        /**
         * Creates a new direct decrypter.
         *
         * @param octJWK The symmetric key, as a JWK. Must be 128 bits (16
         *               bytes), 192 bits (24 bytes), 256 bits (32 bytes), 384
         *               bits (48 bytes) or 512 bits (64 bytes) long. Must not
         *               be {@code null}.
         *
         * @throws KeyLengthException If the symmetric key length is not
         *                            compatible.
         */
        public DirectDecrypter(final OctetSequenceKey octJWK)
                throws KeyLengthException {

                this(octJWK.toSecretKey("AES"));
        }


        /**
         * Creates a new direct decrypter.
         *
         * @param key            The symmetric key. Its algorithm must be
         *                       "AES". Must be 128 bits (16 bytes), 192 bits
         *                       (24 bytes), 256 bits (32 bytes), 384 bits (48
         *                       bytes) or 512 bits (64 bytes) long. Must not
         *                       be {@code null}.
         * @param defCritHeaders The names of the critical header parameters
         *                       that are deferred to the application for
         *                       processing, empty set or {@code null} if none.
         *
         * @throws KeyLengthException If the symmetric key length is not
         *                            compatible.
         */
        public DirectDecrypter(final SecretKey key, final Set<String> defCritHeaders)
                throws KeyLengthException {

                super(key);

                critPolicy.setDeferredCriticalHeaderParams(defCritHeaders);
        }


        @Override
        public Set<String> getProcessedCriticalHeaderParams() {

                return critPolicy.getProcessedCriticalHeaderParams();
        }


        @Override
        public Set<String> getDeferredCriticalHeaderParams() {

                return critPolicy.getProcessedCriticalHeaderParams();
        }


        @Override
        public byte[] decrypt(final JWEHeader header,
                              final Base64URL encryptedKey,
                              final Base64URL iv,
                              final Base64URL cipherText,
                              final Base64URL authTag) 
                throws JOSEException {

                // Validate required JWE parts
                if (encryptedKey != null) {
                        throw new JOSEException("Unexpected present JWE encrypted key");
                }       

                if (iv == null) {
                        throw new JOSEException("Unexpected present JWE initialization vector (IV)");
                }

                if (authTag == null) {
                        throw new JOSEException("Missing JWE authentication tag");
                }
                

                JWEAlgorithm alg = header.getAlgorithm();

                if (! alg.equals(JWEAlgorithm.DIR)) {
                        throw new JOSEException(AlgorithmSupportMessage.unsupportedJWEAlgorithm(alg, SUPPORTED_ALGORITHMS));
                }

                critPolicy.ensureHeaderPasses(header);

                return ContentCryptoProvider.decrypt(header, null, iv, cipherText, authTag, getKey(), getJCAContext());
        }
}