Cellular Network Infrastructure » IMSI Pseudonymization

/* Copyright 2020 sysmocom s.f.m.c. GmbH

 * SPDX-License-Identifier: Apache-2.0 */

package org.osmocom.IMSIPseudo;

import sim.access.*;

import sim.toolkit.*;

import javacard.framework.*;

public class IMSIPseudo extends Applet implements ToolkitInterface, ToolkitConstants {

	// DON'T DECLARE USELESS INSTANCE VARIABLES! They get saved to the EEPROM,

	// which has a limited number of write cycles.

	private byte STKServicesMenuId;

	private SIMView gsmFile;

	static byte[] LUCounter = new byte[] { '0', 'x', ' ', 'L', 'U' };

	/* Main menu */

	static byte[] title = new byte[] { 'I', 'M', 'S', 'I', ' ', 'P', 's', 'e', 'u', 'd', 'o', 'n', 'y', 'm',

					   'i', 'z', 'a', 't', 'i', 'o', 'n'};

	static byte[] showLU = new byte[] {'S', 'h', 'o', 'w', ' ', 'L', 'U', ' ', 'c', 'o', 'u', 'n', 't', 'e', 'r'};

	static byte[] showIMSI = new byte[] {'S', 'h', 'o', 'w', ' ', 'I', 'M', 'S', 'I'};

	static byte[] changeIMSI = new byte[] {'C', 'h', 'a', 'n', 'g', 'e', ' ', 'I', 'M', 'S', 'I', ' '};

	private Object[] itemListMain = {title, showLU, showIMSI, changeIMSI};

	/* Change IMSI menu */

	static byte[] setDigit1 = new byte[] {'S', 'e', 't', ' ', '1', ' ', 'a', 's', ' ', 'l', 'a', 's', 't', ' ',

						  'd', 'i', 'g', 'i', 't'};

	static byte[] setDigit2 = new byte[] {'S', 'e', 't', ' ', '2', ' ', 'a', 's', ' ', 'l', 'a', 's', 't', ' ',

						  'd', 'i', 'g', 'i', 't'};

	private Object[] itemListChangeIMSI = {changeIMSI, setDigit1, setDigit2};

	private IMSIPseudo() {

		gsmFile = SIMSystem.getTheSIMView();

		/* Register menu and trigger on location updates */

		ToolkitRegistry reg = ToolkitRegistry.getEntry();

		STKServicesMenuId = reg.initMenuEntry(title, (short)0, (short)title.length, PRO_CMD_SELECT_ITEM, false,

						 (byte)0, (short)0);

		reg.setEvent(EVENT_EVENT_DOWNLOAD_LOCATION_STATUS);

	}

	public static void install(byte[] bArray, short bOffset, byte bLength) {

		IMSIPseudo applet = new IMSIPseudo();

		applet.register();

	}

	public void process(APDU arg0) throws ISOException {

		if (selectingApplet())

			return;

	}

	public void processToolkit(byte event) throws ToolkitException {

		EnvelopeHandler envHdlr = EnvelopeHandler.getTheHandler();

		if (event == EVENT_MENU_SELECTION) {

			byte selectedItemId = envHdlr.getItemIdentifier();

			if (selectedItemId == STKServicesMenuId) {

				showMenu(itemListMain, (byte)4);

				handleMenuResponseMain();

			}

		}

		if (event == EVENT_EVENT_DOWNLOAD_LOCATION_STATUS) {

			LUCounter[0]++;

			showMsg(LUCounter);

		}

	}

	private void showMenu(Object[] itemList, byte itemCount) {

		ProactiveHandler proHdlr = ProactiveHandler.getTheHandler();

		proHdlr.init((byte) PRO_CMD_SELECT_ITEM,(byte)0,DEV_ID_ME);

		for (byte i=(byte)0;i<itemCount;i++) {

			if (i == 0) {

				/* Title */

				proHdlr.appendTLV((byte)(TAG_ALPHA_IDENTIFIER | TAG_SET_CR), (byte[])itemList[i],

						  (short)0, (short)((byte[])itemList[i]).length);

			} else {

				/* Menu entry */

				proHdlr.appendTLV((byte)(TAG_ITEM | TAG_SET_CR), (byte)i, (byte[])itemList[i], (short)0,

						  (short)((byte[])itemList[i]).length);

			}

		}

		proHdlr.send();

	}

	private void showMsg(byte[] msg) {

		ProactiveHandler proHdlr = ProactiveHandler.getTheHandler();

		proHdlr.initDisplayText((byte)0, DCS_8_BIT_DATA, msg, (short)0, (short)(msg.length));

		proHdlr.send();

	}

	private void showError(short code) {

		byte[] msg = new byte[] {'E', '?', '?'};

		msg[1] = (byte)('0' + code / 10);

		msg[2] = (byte)('0' + code % 10);

		showMsg(msg);

	}

	/* Convert BCD-encoded digit into printable character

	 *  \param[in] bcd A single BCD-encoded digit

	 *  \returns single printable character

	 */

	private byte bcd2char(byte bcd)

	{

		if (bcd < 0xa)

			return (byte)('0' + bcd);

		else

			return (byte)('A' + (bcd - 0xa));

	}

	/* Convert BCD to string.

	 * The given nibble offsets are interpreted in BCD order, i.e. nibble 0 is bcd[0] & 0xf, nibble 1 is bcd[0] >> 4, nibble

	 * 3 is bcd[1] & 0xf, etc..

	 *  \param[out] dst  Output byte array.

	 *  \param[in] dst_ofs  Where to start writing in dst.

	 *  \param[in] dst_len  How many bytes are available at dst_ofs.

	 *  \param[in] bcd  Binary coded data buffer.

	 *  \param[in] start_nibble  Offset to start from, in nibbles.

	 *  \param[in] end_nibble  Offset to stop before, in nibbles.

	 *  \param[in] allow_hex  If false, return false if there are digits other than 0-9.

	 *  \returns true on success, false otherwise

	 */

	private boolean bcd2str(byte dst[], byte dst_ofs, byte dst_len,

				byte bcd[], byte start_nibble, byte end_nibble, boolean allow_hex)

	{

		byte nibble_i;

		byte dst_i = dst_ofs;

		byte dst_end = (byte)(dst_ofs + dst_len);

		boolean rc = true;

		for (nibble_i = start_nibble; nibble_i < end_nibble && dst_i < dst_end; nibble_i++, dst_i++) {

			byte nibble = bcd[(byte)nibble_i >> 1];

			if ((nibble_i & 1) != 0)

				nibble >>= 4;

			nibble &= 0xf;

			if (!allow_hex && nibble > 9)

				rc = false;

			dst[dst_i] = bcd2char(nibble);

		}

		return rc;

	}

	private boolean mi2str(byte dst[], byte dst_ofs, byte dst_len,

			       byte mi[], boolean allow_hex)

	{

		/* The IMSI byte array by example:

		 * 08 99 10 07 00 00 10 74 90

		 *

		 * This is encoded according to 3GPP TS 24.008 10.5.1.4 Mobile

		 * Identity, short the Mobile Identity IEI:

		 *

		 * 08 length for the following MI, in bytes.

		 *  9 = 0b1001

		 *	1 = odd nr of digits

		 *	 001 = MI type = IMSI

		 * 9  first IMSI digit (BCD)

		 *  0 second digit

		 * 1  third

		 * ...

		 *  0 14th digit

		 * 9  15th and last digit

		 *

		 * If the IMSI had an even number of digits:

		 *

		 * 08 98 10 07 00 00 10 74 f0

		 *

		 * 08 length for the following MI, in bytes.

		 *  8 = 0b0001

		 *	0 = even nr of digits

		 *	 001 = MI type = IMSI

		 * 9  first IMSI digit

		 *  0 second digit

		 * 1  third

		 * ...

		 *  0 14th and last digit

		 * f  filler

		 */

		byte bytelen = mi[0];

		byte mi_type = (byte)(mi[1] & 0xf);

		boolean odd_nr_of_digits = ((mi_type & 0x08) != 0);

		byte start_nibble = 2 + 1; // 2 to skip the bytelen, 1 to skip the mi_type

		byte end_nibble = (byte)(2 + bytelen * 2 - (odd_nr_of_digits ? 0 : 1));

		return bcd2str(dst, dst_ofs, dst_len, mi, start_nibble, end_nibble, allow_hex);

	}

	private void showIMSI() {

		/* 3GPP TS 31.102 4.2.2: IMSI */

		byte[] IMSI = new byte[9];

		byte[] msg = {'C', 'u', 'r', 'r', 'e', 'n', 't', ' ', 'I', 'M', 'S', 'I', ':', ' ',

			      ' ', ' ', ' ', ' ', ' ', ' ', ' ', ' ', ' ', ' ', ' ', ' ', ' ', ' ', ' ', ' '};

		gsmFile.select((short) SIMView.FID_DF_GSM);

		gsmFile.select((short) SIMView.FID_EF_IMSI);

		try {

			gsmFile.readBinary((short)0, IMSI, (short)0, (short)9);

		} catch (SIMViewException e) {

			showError(e.getReason());

			return;

		}

		mi2str(msg, (byte)14, (byte)16, IMSI, false);

		showMsg(msg);

	}

	private void handleMenuResponseMain() {

		ProactiveResponseHandler rspHdlr = ProactiveResponseHandler.getTheHandler();

		switch (rspHdlr.getItemIdentifier()) {

			case 1: /* Show LU counter */

				showMsg(LUCounter);

				break;

			case 2: /* Show IMSI */

				showIMSI();

				break;

			case 3: /* Change IMSI */

				showMenu(itemListChangeIMSI, (byte)3);

				handleMenuResponseChangeIMSI();

				break;

		}

	}

	private void handleMenuResponseChangeIMSI() {

		/* TODO */

	}

}