/*

 * Copyright (c) 1997, 2017, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code 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

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

package java.security;

import java.io.*;

/**

 * <p> SignedObject is a class for the purpose of creating authentic

 * runtime objects whose integrity cannot be compromised without being

 * detected.

 *

 * <p> More specifically, a SignedObject contains another Serializable

 * object, the (to-be-)signed object and its signature.

 *

 * <p> The signed object is a "deep copy" (in serialized form) of an

 * original object.  Once the copy is made, further manipulation of

 * the original object has no side effect on the copy.

 *

 * <p> The underlying signing algorithm is designated by the Signature

 * object passed to the constructor and the {@code verify} method.

 * A typical usage for signing is the following:

 *

 * <pre>{@code

 * Signature signingEngine = Signature.getInstance(algorithm,

 *                                                 provider);

 * SignedObject so = new SignedObject(myobject, signingKey,

 *                                    signingEngine);

 * }</pre>

 *

 * <p> A typical usage for verification is the following (having

 * received SignedObject {@code so}):

 *

 * <pre>{@code

 * Signature verificationEngine =

 *     Signature.getInstance(algorithm, provider);

 * if (so.verify(publickey, verificationEngine))

 *     try {

 *         Object myobj = so.getObject();

 *     } catch (java.lang.ClassNotFoundException e) {};

 * }</pre>

 *

 * <p> Several points are worth noting.  First, there is no need to

 * initialize the signing or verification engine, as it will be

 * re-initialized inside the constructor and the {@code verify}

 * method. Secondly, for verification to succeed, the specified

 * public key must be the public key corresponding to the private key

 * used to generate the SignedObject.

 *

 * <p> More importantly, for flexibility reasons, the

 * constructor and {@code verify} method allow for

 * customized signature engines, which can implement signature

 * algorithms that are not installed formally as part of a crypto

 * provider.  However, it is crucial that the programmer writing the

 * verifier code be aware what {@code Signature} engine is being

 * used, as its own implementation of the {@code verify} method

 * is invoked to verify a signature.  In other words, a malicious

 * {@code Signature} may choose to always return true on

 * verification in an attempt to bypass a security check.

 *

 * <p> The signature algorithm can be, among others, the NIST standard

 * DSA, using DSA and SHA-256.  The algorithm is specified using the

 * same convention as that for signatures. The DSA algorithm using the

 * SHA-256 message digest algorithm can be specified, for example, as

 * "SHA256withDSA".  In the case of

 * RSA the signing algorithm could be specified as, for example,

 * "SHA256withRSA".  The algorithm name must be

 * specified, as there is no default.

 *

 * <p> The name of the Cryptography Package Provider is designated

 * also by the Signature parameter to the constructor and the

 * {@code verify} method.  If the provider is not

 * specified, the default provider is used.  Each installation can

 * be configured to use a particular provider as default.

 *

 * <p> Potential applications of SignedObject include:

 * <ul>

 * <li> It can be used

 * internally to any Java runtime as an unforgeable authorization

 * token -- one that can be passed around without the fear that the

 * token can be maliciously modified without being detected.

 * <li> It

 * can be used to sign and serialize data/object for storage outside

 * the Java runtime (e.g., storing critical access control data on

 * disk).

 * <li> Nested SignedObjects can be used to construct a logical

 * sequence of signatures, resembling a chain of authorization and

 * delegation.

 * </ul>

 *

 * @see Signature

 *

 * @author Li Gong

 */

public final class SignedObject implements Serializable {

    private static final long serialVersionUID = 720502720485447167L;

    /*

     * The original content is "deep copied" in its serialized format

     * and stored in a byte array.  The signature field is also in the

     * form of byte array.

     */

    private byte[] content;

    private byte[] signature;

    private String thealgorithm;

    /**

     * Constructs a SignedObject from any Serializable object.

     * The given object is signed with the given signing key, using the

     * designated signature engine.

     *

     * @param object the object to be signed.

     * @param signingKey the private key for signing.

     * @param signingEngine the signature signing engine.

     *

     * @exception IOException if an error occurs during serialization

     * @exception InvalidKeyException if the key is invalid.

     * @exception SignatureException if signing fails.

     */

    public SignedObject(Serializable object, PrivateKey signingKey,

                        Signature signingEngine)

        throws IOException, InvalidKeyException, SignatureException {

            // creating a stream pipe-line, from a to b

            ByteArrayOutputStream b = new ByteArrayOutputStream();

            ObjectOutput a = new ObjectOutputStream(b);

            // write and flush the object content to byte array

            a.writeObject(object);

            a.flush();

            a.close();

            this.content = b.toByteArray();

            b.close();

            // now sign the encapsulated object

            this.sign(signingKey, signingEngine);

    }

    /**

     * Retrieves the encapsulated object.

     * The encapsulated object is de-serialized before it is returned.

     *

     * @return the encapsulated object.

     *

     * @exception IOException if an error occurs during de-serialization

     * @exception ClassNotFoundException if an error occurs during

     * de-serialization

     */

    public Object getObject()

        throws IOException, ClassNotFoundException

    {

        // creating a stream pipe-line, from b to a

        ByteArrayInputStream b = new ByteArrayInputStream(this.content);

        ObjectInput a = new ObjectInputStream(b);

        Object obj = a.readObject();

        b.close();

        a.close();

        return obj;

    }

    /**

     * Retrieves the signature on the signed object, in the form of a

     * byte array.

     *

     * @return the signature. Returns a new array each time this

     * method is called.

     */

    public byte[] getSignature() {

        return this.signature.clone();

    }

    /**

     * Retrieves the name of the signature algorithm.

     *

     * @return the signature algorithm name.

     */

    public String getAlgorithm() {

        return this.thealgorithm;

    }

    /**

     * Verifies that the signature in this SignedObject is the valid

     * signature for the object stored inside, with the given

     * verification key, using the designated verification engine.

     *

     * @param verificationKey the public key for verification.

     * @param verificationEngine the signature verification engine.

     *

     * @exception SignatureException if signature verification failed.

     * @exception InvalidKeyException if the verification key is invalid.

     *

     * @return {@code true} if the signature

     * is valid, {@code false} otherwise

     */

    public boolean verify(PublicKey verificationKey,

                          Signature verificationEngine)

         throws InvalidKeyException, SignatureException {

             verificationEngine.initVerify(verificationKey);

             verificationEngine.update(this.content.clone());

             return verificationEngine.verify(this.signature.clone());

    }

    /*

     * Signs the encapsulated object with the given signing key, using the

     * designated signature engine.

     *

     * @param signingKey the private key for signing.

     * @param signingEngine the signature signing engine.

     *

     * @exception InvalidKeyException if the key is invalid.

     * @exception SignatureException if signing fails.

     */

    private void sign(PrivateKey signingKey, Signature signingEngine)

        throws InvalidKeyException, SignatureException {

            // initialize the signing engine

            signingEngine.initSign(signingKey);

            signingEngine.update(this.content.clone());

            this.signature = signingEngine.sign().clone();

            this.thealgorithm = signingEngine.getAlgorithm();

    }

    /**

     * readObject is called to restore the state of the SignedObject from

     * a stream.

     */

    private void readObject(java.io.ObjectInputStream s)

        throws java.io.IOException, ClassNotFoundException {

            java.io.ObjectInputStream.GetField fields = s.readFields();

            content = ((byte[])fields.get("content", null)).clone();

            signature = ((byte[])fields.get("signature", null)).clone();

            thealgorithm = (String)fields.get("thealgorithm", null);

    }

}