/*
* GidsApplet: A Java Card implementation of the GIDS (Generic Identity
* Device Specification) specification
* https://msdn.microsoft.com/en-us/library/windows/hardware/dn642100%28v=vs.85%29.aspx
* Copyright (C) 2016 Vincent Le Toux(vincent.letoux@mysmartlogon.com)
*
* It has been based on the IsoApplet
* 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 com.mysmartlogon.gidsApplet;
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(tlv, (short)(tagPos+1)) + 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(tlv, (short)(pos+1)) + 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(byte[] buf, short offset) {
if(buf[offset] == (byte)0x82) { // 256..65535
// Check for short overflow
// (In Java, a short is signed: positive values are 0000..7FFF)
return (short)3;
} else if(buf[offset] == (byte)0x81) {
return (short)2;
} else {
return (short)1;
}
}
/**
* \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 getEncodingLengthFieldLength(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;
}
}
/* returns 0 or the size of the BERTLV structure */
public static short CheckBERTLV(byte[] buf, short offset, short len) {
short size = 0;
short sizeforsize = 0;
short i = 1;
short totalsize = 0;
if ((buf[offset] & 0x1F) != 0x1F) {
// simplified tag
} else {
// tag start with all 5 last bits to 1
// skip the tag
while (((buf[(short) (offset + i)] & 0x80) != 0) && i < len) {
i++;
}
// pass the last byte of the tag
i+=1;
}
if ((short) (i+1) >len) {
return 0;
}
// check the size
if ((buf[(short) (offset + i)] & 0x80) != 0) {
// size encoded in many bytes
sizeforsize = (short) (buf[(short) (offset + i)] & 0x7F);
if ((short) (i+1+sizeforsize) >len) {
return 0;
}
if (sizeforsize > (short) 2) {
// more than two bytes for encoding => not something than we can handle
return 0;
} else if (sizeforsize == (short) 1) {
if ((short) (offset + i + 1 + sizeforsize) > len) {
return 0;
}
size = Util.makeShort((byte) 0,buf[(short) (offset + i + 1)]);
} else if (sizeforsize == 2) {
totalsize = (short) (i + 1 + sizeforsize + size);
if ((short) (offset + i + 1 + sizeforsize) > len) {
return (short) 0;
}
size = Util.getShort(buf, (short) (offset + i + 1));
}
} else {
// size encode in one byte
size = Util.makeShort((byte) 0,buf[(short) (offset + i)]);
}
totalsize = (short) (i + 1 + sizeforsize + size);
if (totalsize < (short) 240 && (short) (offset + totalsize) > len) {
return (short) 0;
}
return totalsize;
}
public static boolean IsBERTLVTagEqual(byte[] tag, short offset, short length, byte[] value) {
short i = 1;
// first byte contains the class description
if (tag[offset] != value[(short)0]) {
return false;
}
// simplified tag
if ((value[(short) 0] & 0x1F ) != 0x1F) {
return true;
}
// subsequent bytes starts by 1xxxxxxx until the last byte 0xxxxxxx
while(((short) (offset + i) < length) && (tag[(short) (offset+i)] == value[i]) && ((value[i] & 0x80) != 0)) {
i++;
}
// check if the loop stopped because of 0xxxxxxx or an error
if (((short) (offset + i + 1) <= length) && (tag[(short) (offset+i)] == value[i])) {
return true;
}
return false;
}
/* input data is supposed to have been validaded before */
public static short GetBERTLVDataLen(byte[] buf, short offset, short len) {
short size = 0;
short sizeforsize = 0;
short i = 1;
if ((buf[offset] & 0x1F) != 0x1F) {
// simplified tag
} else {
// tag start with all 5 last bits to 1
// skip the tag
while (((buf[(short) (offset + i)] & 0x80) != 0) && ((short)(i+offset)) < len) {
i++;
}
// pass the last byte of the tag
i+=1;
}
// check the size
if ((buf[(short) (offset + i)] & 0x80) != 0) {
// size encoded in many bytes
sizeforsize = (short) (buf[(short) (offset + i)] & 0x7F);
if (sizeforsize > 2) {
// more than two bytes for encoding => not something than we can handle
return 0;
} else if (sizeforsize == 1) {
size = Util.makeShort((byte) 0,buf[(short) (offset + i + 1)]);
} else if (sizeforsize == 2) {
size = Util.getShort(buf, (short) (offset + i + 1));
}
} else {
// size encode in one byte
size = Util.makeShort((byte) 0,buf[(short) (offset + i)]);
}
return size;
}
}