/*
 * Copyright © 1997 - 1999 IBM Corporation.
 * 
 * Redistribution and use in source (source code) and binary (object code)
 * forms, with or without modification, are permitted provided that the
 * following conditions are met:
 * 1. Redistributed source code must retain the above copyright notice, this
 * list of conditions and the disclaimer below.
 * 2. Redistributed object code must reproduce the above copyright notice,
 * this list of conditions and the disclaimer below in the documentation
 * and/or other materials provided with the distribution.
 * 3. The name of IBM may not be used to endorse or promote products derived
 * from this software or in any other form without specific prior written
 * permission from IBM.
 * 4. Redistribution of any modified code must be labeled "Code derived from
 * the original OpenCard Framework".
 * 
 * THIS SOFTWARE IS PROVIDED BY IBM "AS IS" FREE OF CHARGE. IBM SHALL NOT BE
 * LIABLE FOR INFRINGEMENTS OF THIRD PARTIES RIGHTS BASED ON THIS SOFTWARE.  ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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 * SOFTWARE.
 */
package opencard.opt.security;

/**
 * Credential used by a card service to sign a block of data
 * that matches the key's input length.
 * SignCredentials can for example be used for external authentication.
 * External authentication means that the outside world (the application)
 * authenticates itself by encrypting a challenge (random number) that the card
 * sends to the application.
 * The algorithm used to sign the challenge can either be a symmetric
 * algorithm like DES or an asymmetric public key algorithm (PKA) like RSA.
 * The SignCredential can only sign challenges that match its defined
 * input length (it does neither compute a hash nor pad data).
 * Padding of the challenge up to the defined input length is card specific
 * and is done by the card service.
 */
public interface SignCredential extends opencard.opt.security.Credential {

  /**
   * Sign/encrypt a block of data.
   * @param data The length must match the credential's input length
   *        obtained with getInputLength()
   * @return the signature/cryptogram
   * @exception RuntimeException
   *            A credential must not throw checked exceptions
   *            because otherwise each card service using credentials
   *            would have to declare all possible exceptions.
   */
  byte[] sign(byte[] data) throws RuntimeException;

  /**
   * Return the input length that the cryptographic algorithm can process.
   * @return int
   */
  int getInputLength();

}
