/* Signature.java --- Signature Class
   Copyright (C) 1999, 2002, 2003 Free Software Foundation, Inc.

This file is part of GNU Classpath.

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package java.security;

import java.security.cert.Certificate;
import java.security.cert.X509Certificate;
import java.security.spec.AlgorithmParameterSpec;

import gnu.java.security.Engine;

/**
 * <p>This <code>Signature</code> class is used to provide applications the
 * functionality of a digital signature algorithm. Digital signatures are used
 * for authentication and integrity assurance of digital data.</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 <i>DSA</i> algorithm using the
 * <i>SHA-1</i> message digest algorithm can be specified as <code>SHA1withDSA
 * </code>. 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>MD2withRSA</code>, <code>MD5withRSA</code>, or
 * <code>SHA1withRSA</code>. The algorithm name must be specified, as there is
 * no default.</p>
 *
 * <p>Like other algorithm-based classes in Java Security, <code>Signature</code>
 * provides implementation-independent algorithms, whereby a caller (application
 * code) requests a particular signature algorithm and is handed back a properly
 * initialized <code>Signature</code> object. It is also possible, if desired,
 * to request a particular algorithm from a particular provider. See the
 * <code>getInstance()</code> methods.</p>
 *
 * <p>Thus, there are two ways to request a <code>Signature</code> algorithm
 * object: by specifying either just an algorithm name, or both an algorithm
 * name and a package provider.</p>
 *
 * <p>If just an algorithm name is specified, the system will determine if there
 * is an implementation of the algorithm requested available in the environment,
 * and if there is more than one, if there is a preferred one.</p>
 *
 * <p>If both an algorithm name and a package provider are specified, the system
 * will determine if there is an implementation of the algorithm in the package
 * requested, and throw an exception if there is not.</p>
 *
 * <p>A <code>Signature</code> object can be used to generate and verify digital
 * signatures.</p>
 *
 * <p>There are three phases to the use of a <code>Signature</code> object for
 * either signing data or verifying a signature:</p>
 *
 * <ol>
 *    <li>Initialization, with either
 *      <ul>
 *        <li>a public key, which initializes the signature for verification
 *        (see <code>initVerify()</code>), or</li>
 *        <li>a private key (and optionally a Secure Random Number Generator),
 *        which initializes the signature for signing (see
 *        {@link #initSign(PrivateKey)} and {@link #initSign(PrivateKey, SecureRandom)}
 *        ).</li>
 *      </ul></li>
 *    <li>Updating<br/>
 *      Depending on the type of initialization, this will update the bytes to
 *      be signed or verified. See the update methods.<br/></li>
 *    <li>Signing or Verifying a signature on all updated bytes. See the
 *    <code>sign()</code> methods and the <code>verify()</code> method.</li>
 *  </ol>
 *
 * <p>Note that this class is abstract and extends from {@link SignatureSpi} for
 * historical reasons. Application developers should only take notice of the
 * methods defined in this <code>Signature</code> class; all the methods in the
 * superclass are intended for cryptographic service providers who wish to
 * supply their own implementations of digital signature algorithms.
 *
 * @author Mark Benvenuto <ivymccough@worldnet.att.net>
 */
public abstract class Signature extends SignatureSpi
{
  /** Service name for signatures. */
  private static final String SIGNATURE = "Signature";

  /**
   * Possible <code>state</code> value, signifying that this signature object
   * has not yet been initialized.
   */
  protected static final int UNINITIALIZED = 0;

  // Constructor.
  // ------------------------------------------------------------------------

  /**
   * Possible <code>state</code> value, signifying that this signature object
   * has been initialized for signing.
   */
  protected static final int SIGN = 2;

  /**
   * Possible <code>state</code> value, signifying that this signature object
   * has been initialized for verification.
   */
  protected static final int VERIFY = 3;

  /** Current state of this signature object. */
  protected int state = UNINITIALIZED;

  private String algorithm;
  Provider provider;

  /**
   * Creates a <code>Signature</code> object for the specified algorithm.
   *
   * @param algorithm the standard string name of the algorithm. See Appendix A
   * in the Java Cryptography Architecture API Specification &amp; Reference for
   * information about standard algorithm names.
   */
  protected Signature(String algorithm)
  {
    this.algorithm = algorithm;
    state = UNINITIALIZED;
  }

  /**
   * Generates a <code>Signature</code> object that implements the specified
   * digest algorithm. If the default provider package provides an
   * implementation of the requested digest algorithm, an instance of
   * <code>Signature</code> containing that implementation is returned. If the
   * algorithm is not available in the default package, other packages are
   * searched.
   *
   * @param algorithm the standard name of the algorithm requested. See Appendix
   * A in the Java Cryptography Architecture API Specification &amp; Reference
   * for information about standard algorithm names.
   * @return the new Signature object.
   * @throws NoSuchAlgorithmException if the algorithm is not available in the
   * environment.
   */
  public static Signature getInstance(String algorithm)
    throws NoSuchAlgorithmException
  {
    Provider[] p = Security.getProviders();
    for (int i = 0; i < p.length; i++)
      {
        try
          {
            return getInstance(algorithm, p[i]);
          }
        catch (NoSuchAlgorithmException ignored) {}
      }

    throw new NoSuchAlgorithmException(algorithm);
  }

  /**
   * Generates a <code>Signature</code> object implementing the specified
   * algorithm, as supplied from the specified provider, if such an algorithm
   * is available from the provider.
   *
   * @param algorithm the name of the algorithm requested. See Appendix A in
   * the Java Cryptography Architecture API Specification &amp; Reference for
   * information about standard algorithm names.
   * @param provider the name of the provider.
   * @return the new <code>Signature</code> object.
   * @throws NoSuchAlgorithmException if the algorithm is not available in the
   * package supplied by the requested provider.
   * @throws NoSuchProviderException if the provider is not available in the
   * environment.
   * @throws IllegalArgumentException if the provider name is <code>null</code>
   * or empty.
   * @see Provider
   */
  public static Signature getInstance(String algorithm, String provider)
    throws NoSuchAlgorithmException, NoSuchProviderException
  {
    if (provider == null || provider.length() == 0)
      throw new IllegalArgumentException("Illegal provider");
    
    Provider p = Security.getProvider(provider);
    if (p == null)
      throw new NoSuchProviderException(provider);

    return getInstance(algorithm, p);
  }

  /**
   * Generates a <code>Signature</code> object implementing the specified
   * algorithm, as supplied from the specified provider, if such an algorithm
   * is available from the provider. Note: the provider doesn't have to be
   * registered.
   *
   * @param algorithm the name of the algorithm requested. See Appendix A in
   * the Java Cryptography Architecture API Specification &amp; Reference for
   * information about standard algorithm names.
   * @param provider the provider.
   * @return the new <code>Signature</code> object.
   * @throws NoSuchAlgorithmException if the <code>algorithm</code> is not
   * available in the package supplied by the requested <code>provider</code>.
   * @throws IllegalArgumentException if the <code>provider</code> is
   * <code>null</code>.
   * @since 1.4
   * @see Provider
   */
  public static Signature getInstance(String algorithm, Provider provider)
    throws NoSuchAlgorithmException
  {
    if (provider == null)
      throw new IllegalArgumentException("Illegal provider");

    Signature result = null;
    Object o = null;
    try
      {
        o = Engine.getInstance(SIGNATURE, algorithm, provider);
      }
    catch (java.lang.reflect.InvocationTargetException ite)
      {
        throw new NoSuchAlgorithmException(algorithm);
      }

    if (o instanceof SignatureSpi)
      {
	result = new DummySignature((SignatureSpi) o, algorithm);
      }
    else if (o instanceof Signature)
      {
	result = (Signature) o;
	result.algorithm = algorithm;
      }
    else
      {
	throw new NoSuchAlgorithmException(algorithm);
      }
    result.provider = provider;
    return result;
  }

  /**
   * Returns the provider of this signature object.
   *
   * @return the provider of this signature object.
   */
  public final Provider getProvider()
  {
    return provider;
  }

  /**
   * Initializes this object for verification. If this method is called again
   * with a different argument, it negates the effect of this call.
   *
   * @param publicKey the public key of the identity whose signature is going
   * to be verified.
   * @throws InvalidKeyException if the key is invalid.
   */
  public final void initVerify(PublicKey publicKey) throws InvalidKeyException
  {
    state = VERIFY;
    engineInitVerify(publicKey);
  }

  /**
   * <p>Initializes this object for verification, using the public key from the
   * given certificate.</p>
   *
   * <p>If the certificate is of type <i>X.509</i> and has a <i>key usage</i>
   * extension field marked as <i>critical</i>, and the value of the <i>key
   * usage</i> extension field implies that the public key in the certificate
   * and its corresponding private key are not supposed to be used for digital
   * signatures, an {@link InvalidKeyException} is thrown.</p>
   *
   * @param certificate the certificate of the identity whose signature is
   * going to be verified.
   * @throws InvalidKeyException if the public key in the certificate is not
   * encoded properly or does not include required parameter information or
   * cannot be used for digital signature purposes.
   */
  public final void initVerify(Certificate certificate)
    throws InvalidKeyException
  {
    state = VERIFY;
    if (certificate.getType().equals("X509"))
      {
        X509Certificate cert = (X509Certificate) certificate;
	boolean[]array = cert.getKeyUsage();
	if (array != null && array[0] == false)
	  throw new InvalidKeyException(
              "KeyUsage of this Certificate indicates it cannot be used for digital signing");
      }
    this.initVerify(certificate.getPublicKey());
  }

  /**
   * Initialize this object for signing. If this method is called again with a
   * different argument, it negates the effect of this call.
   *
   * @param privateKey the private key of the identity whose signature is going
   * to be generated.
   * @throws InvalidKeyException if the key is invalid.
   */
  public final void initSign(PrivateKey privateKey) throws InvalidKeyException
  {
    state = SIGN;
    engineInitSign(privateKey);
  }

  /**
   * Initialize this object for signing. If this method is called again with a
   * different argument, it negates the effect of this call.
   *
   * @param privateKey the private key of the identity whose signature is going
   * to be generated.
   * @param random the source of randomness for this signature.
   * @throws InvalidKeyException if the key is invalid.
   */
  public final void initSign(PrivateKey privateKey, SecureRandom random)
    throws InvalidKeyException
  {
    state = SIGN;
    engineInitSign(privateKey, random);
  }

  /**
   * <p>Returns the signature bytes of all the data updated. The format of the
   * signature depends on the underlying signature scheme.</p>
   *
   * <p>A call to this method resets this signature object to the state it was
   * in when previously initialized for signing via a call to
   * <code>initSign(PrivateKey)</code>. That is, the object is reset and
   * available to generate another signature from the same signer, if desired,
   * via new calls to <code>update()</code> and <code>sign()</code>.</p>
   *
   * @return the signature bytes of the signing operation's result.
   * @throws SignatureException if this signature object is not initialized
   * properly.
   */
  public final byte[] sign() throws SignatureException
  {
    if (state == SIGN)
      {
        state = UNINITIALIZED;
        return engineSign();
      }
    else
      throw new SignatureException();
  }

  /**
   * <p>Finishes the signature operation and stores the resulting signature
   * bytes in the provided buffer <code>outbuf</code>, starting at <code>offset
   * </code>. The format of the signature depends on the underlying signature
   * scheme.</p>
   *
   * <p>This signature object is reset to its initial state (the state it was
   * in after a call to one of the <code>initSign()</code> methods) and can be
   * reused to generate further signatures with the same private key.</p>
   *
   * @param outbuf buffer for the signature result.
   * @param offset offset into outbuf where the signature is stored.
   * @param len number of bytes within outbuf allotted for the signature.
   * @return the number of bytes placed into outbuf.
   * @throws SignatureException if an error occurs or len is less than the
   * actual signature length.
   * @since 1.2
   */
  public final int sign(byte[] outbuf, int offset, int len)
    throws SignatureException
  {
    if (state == SIGN)
      {
        state = UNINITIALIZED;
        return engineSign(outbuf, offset, len);
      }
    else
      throw new SignatureException();
  }

  /**
   * <p>Verifies the passed-in signature.</p>
   *
   * <p>A call to this method resets this signature object to the state it was
   * in when previously initialized for verification via a call to
   * <code>initVerify(PublicKey)</code>. That is, the object is reset and
   * available to verify another signature from the identity whose public key
   * was specified in the call to <code>initVerify()</code>.</p>
   *
   * @param signature the signature bytes to be verified.
   * @return <code>true</code> if the signature was verified, <code>false</code>
   * if not.
   * @throws SignatureException if this signature object is not initialized
   * properly, or the passed-in signature is improperly encoded or of the wrong
   * type, etc.
   */
  public final boolean verify(byte[]signature) throws SignatureException
  {
    if (state == VERIFY)
      {
        state = UNINITIALIZED;
        return engineVerify(signature);
      }
    else
      throw new SignatureException();
  }

  /**
   * <p>Verifies the passed-in <code>signature</code> in the specified array of
   * bytes, starting at the specified <code>offset</code>.</p>
   *
   * <p>A call to this method resets this signature object to the state it was
   * in when previously initialized for verification via a call to
   * <code>initVerify(PublicKey)</code>. That is, the object is reset and
   * available to verify another signature from the identity whose public key
   * was specified in the call to <code>initVerify()</code>.</p>
   *
   * @param signature the signature bytes to be verified.
   * @param offset the offset to start from in the array of bytes.
   * @param length the number of bytes to use, starting at offset.
   * @return <code>true</code> if the signature was verified, <code>false</code>
   * if not.
   * @throws SignatureException if this signature object is not initialized
   * properly, or the passed-in <code>signature</code> is improperly encoded or
   * of the wrong type, etc.
   * @throws IllegalArgumentException if the <code>signature</code> byte array
   * is <code>null</code>, or the <code>offset</code> or <code>length</code> is
   * less than <code>0</code>, or the sum of the <code>offset</code> and
   * <code>length</code> is greater than the length of the <code>signature</code>
   * byte array.
   */
  public final boolean verify(byte[] signature, int offset, int length)
    throws SignatureException
  {
    if (state != VERIFY)
      throw new SignatureException("illegal state");

    if (signature == null)
      throw new IllegalArgumentException("signaure is null");
    if (offset < 0)
      throw new IllegalArgumentException("offset is less than 0");
    if (length < 0)
      throw new IllegalArgumentException("length is less than 0");
    if (offset + length < signature.length)
      throw new IllegalArgumentException("range is out of bounds");

    state = UNINITIALIZED;
    return engineVerify(signature, offset, length);
  }

  /**
   * Updates the data to be signed or verified by a byte.
   *
   * @param b the byte to use for the update.
   * @throws SignatureException if this signature object is not initialized
   * properly.
   */
  public final void update(byte b) throws SignatureException
  {
    if (state != UNINITIALIZED)
      engineUpdate(b);
    else
      throw new SignatureException();
  }

  /**
   * Updates the data to be signed or verified, using the specified array of
   * bytes.
   *
   * @param data the byte array to use for the update.
   * @throws SignatureException if this signature object is not initialized
   * properly.
   */
  public final void update(byte[]data) throws SignatureException
  {
    if (state != UNINITIALIZED)
      engineUpdate(data, 0, data.length);
    else
      throw new SignatureException();
  }

  /**
   * Updates the data to be signed or verified, using the specified array of
   * bytes, starting at the specified offset.
   *
   * @param data the array of bytes.
   * @param off the offset to start from in the array of bytes.
   * @param len the number of bytes to use, starting at offset.
   * @throws SignatureException if this signature object is not initialized
   * properly.
   */
  public final void update(byte[]data, int off, int len)
    throws SignatureException
  {
    if (state != UNINITIALIZED)
      engineUpdate(data, off, len);
    else
      throw new SignatureException();
  }

  /**
   * Returns the name of the algorithm for this signature object.
   *
   * @return the name of the algorithm for this signature object.
   */
  public final String getAlgorithm()
  {
    return algorithm;
  }

  /**
   * Returns a string representation of this signature object, providing
   * information that includes the state of the object and the name of the
   * algorithm used.
   *
   * @return a string representation of this signature object.
   */
  public String toString()
  {
    return (algorithm + " Signature");
  }

  /**
   * Sets the specified algorithm parameter to the specified value. This method
   * supplies a general-purpose mechanism through which it is possible to set
   * the various parameters of this object. A parameter may be any settable
   * parameter for the algorithm, such as a parameter size, or a source of
   * random bits for signature generation (if appropriate), or an indication of
   * whether or not to perform a specific but optional computation. A uniform
   * algorithm-specific naming scheme for each parameter is desirable but left
   * unspecified at this time.
   *
   * @param param the string identifier of the parameter.
   * @param value the parameter value.
   * @throws InvalidParameterException if param is an invalid parameter for this
   * signature algorithm engine, the parameter is already set and cannot be set
   * again, a security exception occurs, and so on.
   * @see #getParameter(String)
   * @deprecated Use setParameter(AlgorithmParameterSpec).
   */
  public final void setParameter(String param, Object value)
    throws InvalidParameterException
  {
    engineSetParameter(param, value);
  }

  /**
   * Initializes this signature engine with the specified parameter set.
   *
   * @param params the parameters.
   * @throws InvalidAlgorithmParameterException if the given parameters are
   * inappropriate for this signature engine.
   * @see #getParameters()
   */
  public final void setParameter(AlgorithmParameterSpec params)
    throws InvalidAlgorithmParameterException
  {
    engineSetParameter(params);
  }

  /**
   * <p>Returns the parameters used with this signature object.</p>
   *
   * <p>The returned parameters may be the same that were used to initialize
   * this signature, or may contain a combination of default and randomly
   * generated parameter values used by the underlying signature implementation
   * if this signature requires algorithm parameters but was not initialized
   * with any.
   *
   * @return the parameters used with this signature, or <code>null</code> if
   * this signature does not use any parameters.
   * @see #setParameter(AlgorithmParameterSpec)
   */
  public final AlgorithmParameters getParameters()
  {
    return engineGetParameters();
  }

  /**
   * Gets the value of the specified algorithm parameter. This method supplies
   * a general-purpose mechanism through which it is possible to get the various
   * parameters of this object. A parameter may be any settable parameter for
   * the algorithm, such as a parameter size, or a source of random bits for
   * signature generation (if appropriate), or an indication of whether or not
   * to perform a specific but optional computation. A uniform
   * algorithm-specific naming scheme for each parameter is desirable but left
   * unspecified at this time.
   *
   * @param param the string name of the parameter.
   * @return the object that represents the parameter value, or null if there
   * is none.
   * @throws InvalidParameterException if param is an invalid parameter for this
   * engine, or another exception occurs while trying to get this parameter.
   * @see #setParameter(String, Object)
   * @deprecated
   */
  public final Object getParameter(String param)
    throws InvalidParameterException
  {
    return engineGetParameter(param);
  }

  /**
   * Returns a clone if the implementation is cloneable.
   *
   * @return a clone if the implementation is cloneable.
   * @throws CloneNotSupportedException if this is called on an implementation
   * that does not support {@link Cloneable}.
   */
  public Object clone() throws CloneNotSupportedException
  {
    throw new CloneNotSupportedException();
  }
}