/* SignatureSpi.java --- Signature Service Provider Interface
   Copyright (C) 1999, 2003, Free Software Foundation, Inc.

This file is part of GNU Classpath.

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package java.security;

import java.nio.ByteBuffer;
import java.security.spec.AlgorithmParameterSpec;

/**
 * <code>SignatureSpi</code> defines the Service Provider Interface (SPI) for
 * the {@link Signature} class. The signature class provides an interface to a
 * digital signature algorithm. Digital signatures are used for authentication
 * and integrity of data.
 *
 * @author Mark Benvenuto (ivymccough@worldnet.att.net)
 * @since 1.2
 * @see Signature
 */
public abstract class SignatureSpi
{
  /** Source of randomness. */
  protected SecureRandom appRandom;

  /**
   * Creates a new instance of <code>SignatureSpi</code>.
   */
  public SignatureSpi()
  {
    appRandom = null;
  }

  /**
   * Initializes this instance with the public key for verification purposes.
   * 
   * @param publicKey
   *          the public key to verify with.
   * @throws InvalidKeyException
   *           if the key is invalid.
   */
  protected abstract void engineInitVerify(PublicKey publicKey)
    throws InvalidKeyException;

  /**
   * Initializes this instance with the private key for signing purposes.
   * 
   * @param privateKey
   *          the private key to sign with.
   * @throws InvalidKeyException
   *           if the key is invalid.
   */
  protected abstract void engineInitSign(PrivateKey privateKey)
    throws InvalidKeyException;

  /**
   * Initializes this instance with the private key and source of randomness for
   * signing purposes.
   * 
   * <p>This method cannot be abstract for backward compatibility reasons.</p>
   * 
   * @param privateKey
   *          the private key to sign with.
   * @param random
   *          the {@link SecureRandom} to use.
   * @throws InvalidKeyException
   *           if the key is invalid.
   * @since 1.2
   */
  protected void engineInitSign(PrivateKey privateKey, SecureRandom random)
    throws InvalidKeyException
  {
    appRandom = random;
    engineInitSign(privateKey);
  }

  /**
   * Updates the data to be signed or verified with the specified byte.
   * 
   * @param b
   *          byte to update with.
   * @throws SignatureException
   *           if the engine is not properly initialized.
   */
  protected abstract void engineUpdate(byte b) throws SignatureException;

  /**
   * Updates the data to be signed or verified with the specified bytes.
   * 
   * @param b
   *          the array of bytes to use.
   * @param off
   *          the offset to start at in the array.
   * @param len
   *          the number of the bytes to use from the array.
   * @throws SignatureException
   *           if the engine is not properly initialized.
   */
  protected abstract void engineUpdate(byte[] b, int off, int len)
    throws SignatureException;

  /**
   * Update this signature with the {@link java.nio.Buffer#remaining()}
   * bytes of the given buffer.
   * 
   * @param input The input buffer.
   * @throws IllegalStateException if the engine is not properly initialized.
   */
  protected void engineUpdate(ByteBuffer input)
  {
    byte[] buf = new byte[4096];
    while (input.hasRemaining())
      {
        int l = Math.min(input.remaining(), buf.length);
        input.get(buf, 0, l);
        try
          {
            engineUpdate(buf, 0, l);
          }
        catch (SignatureException se)
          {
            throw new IllegalStateException(se);
          }
      }
  }
  
  /**
   * Returns the signature bytes of all the data fed to this instance. The
   * format of the output depends on the underlying signature algorithm.
   * 
   * @return the signature bytes.
   * @throws SignatureException
   *           if the engine is not properly initialized.
   */
  protected abstract byte[] engineSign() throws SignatureException;

  /**
   * Generates signature bytes of all the data fed to this instance and stores
   * the result in the designated array. The format of the output depends on
   * the underlying signature algorithm.
   * 
   * <p>This method cannot be abstract for backward compatibility reasons.
   * After calling this method, the signature is reset to its initial state and
   * can be used to generate additional signatures.</p>
   * 
   * <p><b>IMPLEMENTATION NOTE:</b>: Neither this method nor the GNU provider
   * will return partial digests. If <code>len</code> is less than the
   * signature length, this method will throw a {@link SignatureException}. If
   * it is greater than or equal then it is ignored.</p>
   * 
   * @param outbuf
   *          the array of bytes to store the result in.
   * @param offset
   *          the offset to start at in the array.
   * @param len
   *          the number of the bytes to use in the array.
   * @return the real number of bytes used.
   * @throws SignatureException
   *           if the engine is not properly initialized.
   * @since 1.2
   */
  protected int engineSign(byte[] outbuf, int offset, int len)
    throws SignatureException
  {
    byte[] tmp = engineSign();
    if (tmp.length > len)
      throw new SignatureException("Invalid Length");

    System.arraycopy(outbuf, offset, tmp, 0, tmp.length);
    return tmp.length;
  }

  /**
   * Verifies a designated signature.
   * 
   * @param sigBytes
   *          the signature bytes to verify.
   * @return <code>true</code> if verified, <code>false</code> otherwise.
   * @throws SignatureException
   *           if the engine is not properly initialized or if it is the wrong
   *           signature.
   */
  protected abstract boolean engineVerify(byte[] sigBytes)
    throws SignatureException;

  /**
   * Convenience method which calls the method with the same name and one
   * argument after copying the designated bytes into a temporary byte array.
   * Subclasses may override this method for performance reasons.
   * 
   * @param sigBytes
   *          the array of bytes to use.
   * @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 verified, <code>false</code> otherwise.
   * @throws SignatureException
   *           if the engine is not properly initialized.
   */
  protected boolean engineVerify(byte[] sigBytes, int offset, int length)
    throws SignatureException
  {
    byte[] tmp = new byte[length];
    System.arraycopy(sigBytes, offset, tmp, 0, length);
    return engineVerify(tmp);
  }

  /**
   * Sets the specified algorithm parameter to the specified value.
   * 
   * @param param
   *          the parameter name.
   * @param value
   *          the parameter value.
   * @throws InvalidParameterException
   *           if the parameter invalid, the parameter is already set and
   *           cannot be changed, a security exception occured, etc.
   * @deprecated use the other setParameter.
   */
  protected abstract void engineSetParameter(String param, Object value)
    throws InvalidParameterException;

  /**
   * Sets the signature engine with the specified {@link AlgorithmParameterSpec}.
   * 
   * <p>This method cannot be abstract for backward compatibility reasons. By
   * default it always throws {@link UnsupportedOperationException} unless
   * overridden.</p>
   * 
   * @param params
   *          the parameters.
   * @throws InvalidParameterException
   *           if the parameter is invalid, the parameter is already set and
   *           cannot be changed, a security exception occured, etc.
   */
  protected void engineSetParameter(AlgorithmParameterSpec params)
    throws InvalidAlgorithmParameterException
  {
    throw new UnsupportedOperationException();
  }

  /**
   * The default implementaion of this method always throws a
   * {@link UnsupportedOperationException}. It MUST be overridden by concrete
   * implementations to return the appropriate {@link AlgorithmParameters} for
   * this signature engine (or <code>null</code> when that engine does not use
   * any parameters.
   * 
   * @return the parameters used with this signature engine, or
   *         <code>null</code> if it does not use any parameters.
   * @throws UnsupportedOperationException
   *           always.
   */
  protected AlgorithmParameters engineGetParameters()
  {
    throw new UnsupportedOperationException();
  }

  /**
   * Returns the value for the specified algorithm parameter.
   * 
   * @param param
   *          the parameter name.
   * @return the parameter value.
   * @throws InvalidParameterException
   *           if the parameter is invalid.
   * @deprecated use the other getParameter
   */
  protected abstract Object engineGetParameter(String param)
    throws InvalidParameterException;

  /**
   * Returns a clone of this instance.
   * 
   * @return a clone of this instance.
   * @throws CloneNotSupportedException
   *           if the implementation does not support cloning.
   */
  public Object clone() throws CloneNotSupportedException
  {
    return super.clone();
  }
}