/*
* IsoApplet: A Java Card PKI applet aimiing for ISO 7816 compliance.
* Copyright (C) 2014 Philip Wendland (wendlandphilip@gmail.com)
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software Foundation,
* Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
package net.pwendland.javacard.pki.isoapplet;
import javacard.framework.Util;
/**
* \brief Utility class for TLV-realted operations.
*/
public class UtilTLV {
/** \brief Find the position of the tag at level 1.
*
* \attention This method only searches level 1 of TLV encoded arrays (i.e. no nested TLVs are searched).
*
* \param tlv The array containing the TLV-encoded object to search.
*
* \param tlvOffset The position at which the TLV structure begins.
*
* \param tlvLength The length of the TLV structure.
*
* \param tag The tag to search for.
*
* \return The position of the tag.
*
* \throw NotFoundException If the tag could not be found.
*
* \throw InvalidArgumentsException Malformatted TLV data.
*/
public static short findTag(byte[] tlv, short tlvOffset, short tlvLength, byte tag) throws NotFoundException, InvalidArgumentsException {
short tagPos = tlvOffset;
short len;
while(tagPos < (short)(tlvLength+tlvOffset-1)) {
if(tlv[tagPos] == tag) {
return tagPos;
}
len = decodeLengthField(tlv, (short)(tagPos+1));
// Increase the position by: T length (1), L length, V length.
// I.e. look at the next Tag, jump over current L and V field.
// This saves execution time and ensures that no byte from V is misinterpreted.
tagPos += 1 + getLengthFieldLength(len) + len;
}
throw NotFoundException.getInstance();
}
/**
* \brief Check the consistency of the TLV structure.
*
* Basically, we jump from one tag to the next. At the end, we must be at the position
* where the next tag would be, if it was there. If the position is any other than that,
* the TLV structure is not consistent.
*
* \param tlv The array containing the TLV-encoded object to search.
*
* \param offset The position at which the TLV structure begins.
*
* \param length The length of the TLV structure.
*
* \return True if the TLV structure is valid, else false.
*/
public static boolean isTLVconsistent(byte[] tlv, short offset, short length) {
short pos = offset;
short len;
while(pos < (short)(length+offset-1)) {
try {
len = decodeLengthField(tlv, (short)(pos+1));
pos += 1 + getLengthFieldLength(len) + len;
} catch (InvalidArgumentsException e) {
return false;
}
}
return (pos == (short)(offset+length));
}
/**
* \brief Decode the length field of a TLV-entry.
*
* The length field itself can be 1, 2 or 3 bytes long:
* - If the length is between 0 and 127, it is 1 byte long.
* - If the length is between 128 and 255, it is 2 bytes long.
* The first byte is 0x81 to indicate this.
* - If the length is between 256 and 65535, it is 3 bytes long.
* The first byte is 0x82, the following 2 contain the actual length.
* Note: Only lengths up to 0x7FFF (32767) are supported here, because a short in Java is signed.
*
* \param buf The buffer containing the length field.
*
* \param offset The offset at where the length field starts.
*
* \param length The length of the buffer (buf). This is to prevent that the index gets out of bounds.
*
* \return The (positive) length encoded by the length field, or in case of an error, -1.
*
* \throw InvalidArgumentsException If offset is too big for a signed Java short
* If the first byte of the length field is invalid
*/
public static short decodeLengthField(byte[] buf, short offset) throws InvalidArgumentsException {
if(buf[offset] == (byte)0x82) { // 256..65535
// Check for short overflow
// (In Java, a short is signed: positive values are 0000..7FFF)
if(buf[(short)(offset+1)] < 0) { // 80..FF
throw InvalidArgumentsException.getInstance();
}
return Util.getShort(buf, (short)(offset+1));
} else if(buf[offset] == (byte)0x81) {
return (short) ( 0x00FF & buf[(short)(offset+1)]);
} else if(buf[offset] > 0) { // 00..7F
return (short) ( 0x007F & buf[offset]);
} else {
throw InvalidArgumentsException.getInstance();
}
}
/**
* \brief Get the length of the length field of a TLV-entry.
*
* \attention Not the length of the value-field is returned,
* but the length of the length field itself.
*
* \see decodeLengthField()
*
* \param length The decoded length from the TLV-entry.
*
* \return The length of the length field.
*
* \throw InvalidArgumentsException If the length would overflow the signed
* short of Java.
*/
public static short getLengthFieldLength(short length) throws InvalidArgumentsException {
if(length < 0) {
throw InvalidArgumentsException.getInstance();
} else if(length < 128) {
return 1;
} else if(length < 256) {
return 2;
} else {
return 3;
}
}
/**
* \brief Write the tag and length to a buffer.
*
* Only the tag and length field are written. The writing of the value field is left to the caller.
*
* \param tag A one- or two-byte tag.
*
* \param len The length that should be written to the length field.
*
* \param out The buffer to write the result to.
*
* \param outLen The length of out.
*
* \param outOffset The offset at which to start writing the tag.
*
* \return The length that was written.
*
* \throw InvalidArgumentsException If the tag is invalid.
* If len is negative.
*
* \throw NotEnoughSpaceException If the buffer "out" is too small.
*/
public static short writeTagAndLen(short tag, short len, byte[] out, short outOffset) throws InvalidArgumentsException, NotEnoughSpaceException {
byte tagLen;
short pos = outOffset;
short outLen = (short)out.length;
if((short)(tag & (short)0xFF00) != 0) {
if((short)(tag & (short)0x1F00) != (short)0x1F00) {
/* Missing escape marker */
throw InvalidArgumentsException.getInstance();
}
tagLen = 2;
} else {
tagLen = 1;
}
if(len < 0) {
throw InvalidArgumentsException.getInstance();
}
if((short)(tagLen + getLengthFieldLength(len)) > (short)(outLen - outOffset)) {
throw NotEnoughSpaceException.getInstance();
}
if(tagLen == 1) {
out[pos] = (byte)(tag & (short)0x00FF);
} else {
Util.setShort(out, pos, tag);
}
pos += tagLen;
if(len < 128) {
out[pos++] = (byte)(len & (short)0x007F);
} else if(len < 256) {
out[pos++] = (byte)0x81;
out[pos++] = (byte)(len & (short)0x00FF);
} else {
out[pos++] = (byte)0x82;
Util.setShort(out, pos, len);
pos += 2;
}
return (short)(pos - outOffset);
}
}