ASN1.java

//  SmartCard Applet
//      Authors:          Robert Relyea     <rrelyea@redhat.com>
//      Package:          CardEdgeApplet
//      Description:      CardEdge implementation with JavaCard
//
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package com.redhat.ckey.applet;

import javacard.framework.ISOException;
import javacard.framework.JCSystem;
import javacard.framework.Util;

/**
 * ASN1 parser Class
 *
 * <p>This Simplistic ASN.1 parser does not interpret tags, it simply finds
 * elements based on where their fields are supposed to wind up at. </p>
 *
 *
 * Object fields:
 * <pre>
 *    short[] newSize; // way to get around java's restrictions on pass by ref. 
 *    byte[] data
 * </pre>
 *
 * @author Robert Relyea
 * @version 0.0.1
 *
 */
public class ASN1
{
    public static final short SW_BAD_DER_DATA = (short)0x9cd0;
    private final short NEXT = 0;
    private final short SIZE = 1;
    private final short END  = 2;
    private short[] params;

    public ASN1() 
    {
	params=JCSystem.makeTransientShortArray((short)3,
						JCSystem.CLEAR_ON_DESELECT);
    }
  
    public short GetEnd()
    {
	return params[END];
    } 

    public short GetSize()
    {
	return params[SIZE];
    } 

    public short GetNext()
    {
	return params[NEXT];
    } 

    public byte GetTag(byte buf[], short offset, short end)
    {
	if (end <= offset) {
	    ISOException.throwIt(SW_BAD_DER_DATA);
	}
	return buf[offset];
    }
	
    public short Unwrap(byte buf[], short offset, short end, short dbg)
    {
	byte tag;
	byte len;
	short length = 0;

	if (end < (short)(offset+2)) {
	    ISOException.throwIt(SW_BAD_DER_DATA);
	}
	tag = buf[offset++];
	if (tag == 0) {
	    ISOException.throwIt(SW_BAD_DER_DATA);
	}
	len = buf[offset++];
	length = Util.makeShort((byte)0,len);

	if ((len & 0x80) != 0) {
	    short count = Util.makeShort((byte)0,(byte)(len & 0x7f));
	    if (end < (short)(offset+count)) {
	        ISOException.throwIt(SW_BAD_DER_DATA);
	    }
	    if (count > 2) {
	        ISOException.throwIt(SW_BAD_DER_DATA);
	    }
            length = 0;
	    while (count-- > 0) {
		length = (short)((length << 8) 
				| Util.makeShort((byte)0,buf[offset++]));
	    }
	}
	params[SIZE] = length;
	params[NEXT] = ((short)(offset+length));
	params[END] = ((short)(offset+length));
	return offset;
    }

    public short Skip(byte buf[], short offset, short end, short dbg)
    {
	Unwrap(buf,offset,end,dbg);
	return params[NEXT];
    }

    public short UnwrapBitString(byte buf[], short offset, short end, short dbg)
    {
	if (buf[offset] != 0) {
	    ISOException.throwIt(SW_BAD_DER_DATA);
	}
	if (end < (short)(offset+1)) {
	    ISOException.throwIt(SW_BAD_DER_DATA);
	}
	params[SIZE]--;
	return (short)(offset+1);
    }

    public short Signed2Unsigned(byte buf[], short offset, short end, short dbg)
    {
	short startOffset = offset;
	short startSize=params[SIZE];
	for (; offset < end && buf[offset] == 0 ; offset++){
	    params[SIZE]--;
	}
	if (offset >= end) {
	    ISOException.throwIt(SW_BAD_DER_DATA);
	}
	return offset;
    }
}