gcc/libjava/java/security/SignedObject.java

/* SignedObject.java --- Signed Object Class
   Copyright (C) 1999, 2003, Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
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any later version.

GNU Classpath is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
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General Public License for more details.

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Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
02111-1307 USA.

Linking this library statically or dynamically with other modules is
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As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
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terms of your choice, provided that you also meet, for each linked
independent module, the terms and conditions of the license of that
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exception statement from your version. */

package java.security;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.ObjectInput;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;

/**
 * <p><code>SignedObject</code> is a class for the purpose of creating authentic
 * runtime objects whose integrity cannot be compromised without being detected.
 * </p>
 *
 * <p>More specifically, a <code>SignedObject</code> contains another
 * {@link Serializable} object, the (to-be-)signed object and its signature.</p>
 *
 * <p>The signed object is a <i>"deep copy"</i> (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>
 *
 * <p>The underlying signing algorithm is designated by the {@link Signature}
 * object passed to the constructor and the <code>verify()</code> method. A
 * typical usage for signing is the following:</p>
 *
 * <pre>
 * 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
 * <code>SignedObject</code> so):</p>
 *
 * <pre>
 * Signature verificationEngine = Signature.getInstance(algorithm, provider);
 * if (so.verify(publickey, verificationEngine))
 *   try
 *     {
 *       Object myobj = so.getObject();
 *     }
 *   catch (ClassNotFoundException ignored) {};
 * </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()</code> method. Secondly, for verification
 * to succeed, the specified public key must be the public key corresponding to
 * the private key used to generate the <code>SignedObject</code>.</p>
 *
 * <p>More importantly, for flexibility reasons, the <code>constructor</code>
 * and <code>verify()</code> 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 {@link Signature} engine is being used, as
 * its own implementation of the <code>verify()</code> method is invoked to
 * verify a signature. In other words, a malicious {@link Signature} may choose
 * to always return <code>true</code> on verification in an attempt to bypass a
 * security check.</p>
 *
 * <p>The signature algorithm can be, among others, the NIST standard <i>DSS</i>,
 * using <i>DSA</i> and <i>SHA-1</i>. The algorithm is specified using the same
 * convention as that for signatures. The <i>DSA</i> algorithm using the
 * </i>SHA-1</i> message digest algorithm can be specified, for example, as
 * <code>"SHA/DSA"</code> or <code>"SHA-1/DSA"</code> (they are equivalent). In
 * the case of <i>RSA</i>, there are multiple choices for the message digest
 * algorithm, so the signing algorithm could be specified as, for example,
 * <code>"MD2/RSA"</code>, <code>"MD5/RSA"</code> or <code>"SHA-1/RSA"</code>.
 * The algorithm name must be specified, as there is no default.</p>
 *
 * <p>The name of the Cryptography Package Provider is designated also by the
 * {@link Signature} parameter to the <code>constructor</code> and the <code>
 * verify()</code> 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>
 *
 * <p>Potential applications of <code>SignedObject</code> include:</p>
 *
 * <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>
 *  <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>
 *  <li>Nested <i>SignedObjects</i> can be used to construct a logical sequence
 *  of signatures, resembling a chain of authorization and delegation.</li>
 * </ul>
 *
 * @author Mark Benvenuto <ivymccough@worldnet.att.net>
 * @since 1.2
 * @see Signature
 */
public final class SignedObject implements Serializable
{
  private static final long serialVersionUID = 720502720485447167L;

  /** @serial */
  private byte[] content;
  /** @serial */
  private byte[] signature;
  /** @serial */
  private String thealgorithm;

  /**
   * Constructs a <code>SignedObject</code> from any {@link 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.
   * @throws IOException if an error occurs during serialization.
   * @throws InvalidKeyException if the key is invalid.
   * @throws SignatureException if signing fails.
   */
  public SignedObject(Serializable object, PrivateKey signingKey,
		      Signature signingEngine)
    throws IOException, InvalidKeyException, SignatureException
  {
    thealgorithm = signingEngine.getAlgorithm();

    ByteArrayOutputStream ostream = new ByteArrayOutputStream();
    ObjectOutputStream p = new ObjectOutputStream(ostream);
    p.writeObject(object);
    p.flush();
    p.close();

    content = ostream.toByteArray();

    signingEngine.initSign(signingKey);
    signingEngine.update(content);
    signature = signingEngine.sign();
  }

  /**
   * Retrieves the encapsulated object. The encapsulated object is de-serialized
   * before it is returned.
   *
   * @return the encapsulated object.
   * @throws IOException if an error occurs during de-serialization.
   * @throws ClassNotFoundException if an error occurs during de-serialization.
   */
  public Object getObject() throws IOException, ClassNotFoundException
  {
    ByteArrayInputStream bais = new ByteArrayInputStream(content);
    ObjectInput oi = new ObjectInputStream(bais);
    Object obj = oi.readObject();
    oi.close();
    bais.close();

    return obj;
  }

  /**
   * Retrieves the signature on the signed object, in the form of a byte array.
   *
   * @return a copy of the signature.
   */
  public byte[] getSignature()
  {
    return (byte[]) signature.clone();

  }

  /**
   * Retrieves the name of the signature algorithm.
   *
   * @return the signature algorithm name.
   */
  public String getAlgorithm()
  {
    return thealgorithm;
  }

  /**
   * Verifies that the signature in this <code>SignedObject</code> 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.
   * @return <code>true</code> if the signature is valid, <code>false</code>
   * otherwise.
   * @throws SignatureException if signature verification failed.
   * @throws InvalidKeyException if the verification key is invalid.
   */
  public boolean verify(PublicKey verificationKey, Signature verificationEngine)
    throws InvalidKeyException, SignatureException
  {
    verificationEngine.initVerify(verificationKey);
    verificationEngine.update(content);
    return verificationEngine.verify(signature);
  }

  /** Called to restore the state of the SignedObject from a stream. */
  private void readObject(ObjectInputStream s)
    throws IOException, ClassNotFoundException
  {
    s.defaultReadObject();
    content = (byte[]) content.clone();
    signature = (byte[]) signature.clone();
  }
}