itextpdf-master/itext/src/main/java/com/itextpdf/text/pdf/security/TSAClient.java
/*
 *
 * This file is part of the iText (R) project.
    Copyright (c) 1998-2022 iText Group NV
 * Authors: Bruno Lowagie, Paulo Soares, et al.
 *
 * This program is free software; you can redistribute it and/or modify
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package com.itextpdf.text.pdf.security;

import java.security.GeneralSecurityException;
import java.security.MessageDigest;

/**
 * Time Stamp Authority client (caller) interface.
 * <p>
 * Interface used by the PdfPKCS7 digital signature builder to call
 * Time Stamp Authority providing RFC 3161 compliant time stamp token.
 * @author Martin Brunecky, 07/17/2007
 * @since	2.1.6
 */
public interface TSAClient {
    /**
     * Get the time stamp token size estimate.
     * Implementation must return value large enough to accomodate the entire token
     * returned by getTimeStampToken() _prior_ to actual getTimeStampToken() call.
     * @return	an estimate of the token size
     */
    public int getTokenSizeEstimate();
    
    /**
     * Gets the MessageDigest to digest the data imprint
     * @return the digest algorithm name
     */
    public MessageDigest getMessageDigest() throws GeneralSecurityException;
    
    /**
     * Get RFC 3161 timeStampToken.
     * Method may return null indicating that timestamp should be skipped.
     * @param imprint byte[] - data imprint to be time-stamped
     * @return byte[] - encoded, TSA signed data of the timeStampToken
     * @throws Exception - TSA request failed
     */
    public byte[] getTimeStampToken(byte[] imprint) throws Exception;
    
}
