signature.java

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      {
	java.security.cert.X509Certificate cert =
	  (java.security.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());
  }

  /**
     Initializes this class with the private key for 
     signing purposes.

     @param privateKey the private key to sign with

     @throws InvalidKeyException invalid key
   */
  public final void initSign(PrivateKey privateKey) throws InvalidKeyException
  {
    state = SIGN;
    engineInitSign(privateKey);
  }

  /**
     Initializes this class with the private key and source 
     of randomness for signing purposes.

     @param privateKey the private key to sign with
     @param random Source of randomness

     @throws InvalidKeyException invalid key

     @since JDK 1.2
   */
  public final void initSign(PrivateKey privateKey, SecureRandom random)
    throws InvalidKeyException
  {
    state = SIGN;
    engineInitSign(privateKey, random);
  }


  /**
     Returns the signature bytes of all the data fed to this class.
     The format of the output depends on the underlying signature
     algorithm.

     @return the signature

     @throws SignatureException engine not properly initialized
   */
  public final byte[] sign() throws SignatureException
  {
    if (state == SIGN)
      {
	state = UNINITIALIZED;
	return engineSign();
      }
    else
      throw new SignatureException();
  }

  /**
     Generates signature bytes of all the data fed to this class 
     and outputs it to the passed array. The format of the 
     output depends on the underlying signature algorithm.

     After calling this method, the signature is reset to its
     initial state and can be used to generate additional
     signatures.

     @param outbuf array of bytes
     @param offset the offset to start at in the array
     @param len the length of the bytes to put into the array. 
     Neither this method or the GNU provider will 
     return partial digests. If len is less than the 
     signature length, this method will throw 
     SignatureException. If it is greater than or equal
     then it is ignored.

     @return number of bytes in outbuf

     @throws SignatureException engine not properly initialized

     @since JDK 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();
  }

  /**
     Verifies the passed signature.

     @param signature the signature bytes to verify

     @return true if verified, false otherwise

     @throws SignatureException engine not properly initialized
     or wrong signature
   */
  public final boolean verify(byte[]signature) throws SignatureException
  {
    if (state == VERIFY)
      {
	state = UNINITIALIZED;
	return engineVerify(signature);
      }
    else
      throw new SignatureException();
  }

  /**
     Updates the data to be signed or verified with the specified 
     byte.

     @param b byte to update with

     @throws SignatureException Engine not properly initialized
   */
  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 with the specified 
     bytes.

     @param data array of bytes

     @throws SignatureException engine not properly initialized
   */
  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 with the specified 
     bytes.

     @param data array of bytes
     @param off the offset to start at in the array
     @param len the length of the bytes to use in the array

     @throws SignatureException engine not properly initialized
   */
  public final void update(byte[]data, int off, int len)
    throws SignatureException
  {
    if (state != UNINITIALIZED)
      engineUpdate(data, off, len);
    else
      throw new SignatureException();
  }

  /** 
     Gets the name of the algorithm currently used.
     The names of algorithms are usually SHA/DSA or SHA/RSA.

     @return name of algorithm.
   */
  public final String getAlgorithm()
  {
    return algorithm;
  }

  /**
     Returns a representation of the Signature as a String

     @return a string representing the signature
   */
  public String toString()
  {
    return (algorithm + " Signature");
  }

  /**
     Sets the specified algorithm parameter to the specified value.

     @param param parameter name
     @param value parameter value

     @throws InvalidParameterException invalid parameter, parameter 
     already set and cannot set again, a security exception, 
     etc.

     @deprecated use the other setParameter
   */
  public final void setParameter(String param, Object value)
    throws InvalidParameterException
  {
    engineSetParameter(param, value);
  }

  /**
     Sets the signature engine with the specified 
     AlgorithmParameterSpec;

     By default this always throws UnsupportedOperationException 
     if not overridden;

     @param params the parameters

     @throws InvalidParameterException invalid parameter, parameter 
     already set and cannot set again, a security exception, 
     etc.
   */
  public final void setParameter(AlgorithmParameterSpec params)
    throws InvalidAlgorithmParameterException
  {
    engineSetParameter(params);
  }

  /**
     Gets the value for the specified algorithm parameter.

     @param param parameter name

     @return parameter value

     @throws InvalidParameterException invalid parameter

     @deprecated use the other getParameter
   */
  public final Object getParameter(String param)
    throws InvalidParameterException
  {
    return engineGetParameter(param);
  }

  /**
     Returns a clone if cloneable.

     @return a clone if cloneable.

     @throws CloneNotSupportedException if the implementation does 
     not support cloning
   */
  public Object clone() throws CloneNotSupportedException
  {
    throw new CloneNotSupportedException();
  }
}