packet.java

面向应用的智能安全代理平台和工具包是一个综合网络应用的安全共性需求而设计和实现的一个通用性的网络信息安全应用支撑平台

package au.net.aba.pgp;

/*
 * $Id: Packet.java,v 1.2 1998/10/19 06:32:40 leachbj Exp $
 * $Author: leachbj $
 *
 * Copyright (C) 1996-1998 Australian Business Access Pty Ltd.
 * All rights reserved.
 * 
 * Use, modification, copying and distribution of this software is subject the
 * terms and conditions of the ABA Public Licence. See the file
 * "PUBLIC_LICENCE" for additional information.
 *
 * If you have not received a copy of the Public Licence, you must destroy all
 * copies of this file immediately. 
 *
 * $Source: /aba/CVSROOT/jdk1.1/src/au.net.aba/pgp/Packet.java,v $
 * $Revision: 1.2 $
 * $Date: 1998/10/19 06:32:40 $
 * $State: Exp $
 */

import java.io.*;


//
// Generic PGP packet.
//

class Packet
{
	public final static String ident = "$Id: Packet.java,v 1.2 1998/10/19 06:32:40 leachbj Exp $";

	//
	// Read a cipher packet header and build a data stream
	// for the remainder of the packet.
	//
	static DataInputStream buildCipherPacketInputStream (
		InputStream input, byte typeExpected, String errorMessage)
		throws IOException
	{
		// read cipher type byte
		DataInputStream data = new DataInputStream (input);
		byte ctb = data.readByte ();

		// sanity check
		if ((ctb & 0x80) == 0){
			throw new IOException ("not2 in PGP format " + ctb);
		}

		// extract type field
		byte type = (byte)((ctb & 0x3c) >>> 2);

		// check type field
		if (type != typeExpected){
			throw new IOException (errorMessage);
		}

		// read length field
		long length = ~0L;
		switch ((byte)(ctb & 0x03)){
		case 0x00:
			length = data.readByte ();
			break;

		case 0x01:
			length = data.readUnsignedShort ();
			break;

		case 0x02:
			length = data.readUnsignedShort () << 16;
			length |= data.readUnsignedShort ();
			break;
		}

		// length field provided?
		if (length != ~0L){
			// read rest of packet data
			byte[] buffer = new byte[(int)length];
			data.readFully (buffer);

			// use buffer as packet input stream
			data = new DataInputStream (
				new ByteArrayInputStream (buffer));
		}

		return (data);
	}
	//
	// Read a generic cipher packet.
	//
	public static Packet readCipherPacket (InputStream input)
		throws IOException
	{
		// peek at cipher type byte
		// pushback streams are buggy so we make do...
		input.mark (1);
		int ctb = input.read ();
		if (ctb == -1){
			throw new EOFException ();
		}
		input.reset ();

		// sanity check
		if ((ctb & 0x80) == 0){
			throw new IOException ("not1 in PGP format " + ctb);
		}

		// extract type field
		byte type = (byte)((ctb & 0x3c) >>> 2);

		// parse packet
		Packet packet = null;
		switch (type){
		case 0x02:
			packet = new SignaturePacket (input);
			break;

		case 0x05:
			packet = new SecretKeyCertificatePacket (input);
			break;

		case 0x06:
			packet = new PublicKeyCertificatePacket (input);
			break;

		case 0x0c:
			packet = new KeyringTrustPacket (input);
			break;

		case 0x0d:
			packet = new UserIDPacket (input);
			break;

		case 0x0e:
			// skip packet
			buildCipherPacketInputStream (input,(byte)0x09,"panic");
			break;

		default:
			throw new IOException (
				"unrecognised PGP packet " + type);
		}

		return (packet);
	}
}