Cellular Network Infrastructure » IMSI Pseudonymization

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

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

package org.osmocom.IMSIPseudo;

import org.osmocom.IMSIPseudo.MobileIdentity;

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 = { '0', 'x', ' ', 'L', 'U' };

	/* Main menu */

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

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

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

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

	private static final byte[] invalidIMSI = {'I', 'n', 'v', 'a', 'l', 'i', 'd', ' ', 'I', 'M', 'S', 'I'};

	private static final byte[] noChange = {'N', 'o', ' ', 'c', 'h', 'a', 'n', 'g', 'e'};

	private static final byte[] changed = {'I', 'M', 'S', 'I', ' ', 'c', 'h', 'a', 'n', 'g', 'e', 'd', '!'};

	private static final byte error[] = {'E', 'R', 'R', 'O', 'R' };

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

	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);

				handleMenuResponseMain();

			}

		}

		if (event == EVENT_EVENT_DOWNLOAD_LOCATION_STATUS) {

			LUCounter[0]++;

			showMsg(LUCounter);

		}

	}

	private void showMenu(Object[] itemList) {

		ProactiveHandler proHdlr = ProactiveHandler.getTheHandler();

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

		for (byte i=(byte)0; i < itemList.length; 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 byte[] getResponse()

	{

		ProactiveResponseHandler rspHdlr = ProactiveResponseHandler.getTheHandler();

		byte[] resp = new byte[rspHdlr.getTextStringLength()];

		rspHdlr.copyTextString(resp, (short)0);

		return resp;

	}

	/*

	This was used to find out that the first byte of a text field seems to be 4.

	private byte[] getResponseDBG()

	{

		ProactiveResponseHandler rspHdlr;

		byte resp[];

		byte strlen = -1;

		rspHdlr = ProactiveResponseHandler.getTheHandler();

		for (byte occurence = 1; occurence <= 3; occurence++) {

			short len;

			try {

				if (rspHdlr.findTLV(TAG_TEXT_STRING, (byte)occurence) != TLV_NOT_FOUND) {

					if ((len = rspHdlr.getValueLength()) > 1) {

						len = 3;

						resp = new byte[len];

						rspHdlr.copyValue((short)0, resp, (short)0, (short)(len));

						showMsg(resp);

						showMsgAndWaitKey(Bytes.hexdump(resp));

						return resp;

					}

				}

			} catch (Exception e) {

				showError((short)(30 + occurence));

				return null;

			}

		}

		showError((short)(39));

		return null;

	}

	*/

	private byte[] showMsgAndWaitKey(byte[] msg) {

		ProactiveHandler proHdlr = ProactiveHandler.getTheHandler();

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

		proHdlr.send();

		return getResponse();

	}

	private byte[] prompt(byte[] msg, byte[] prefillVal, short minLen, short maxLen) {

		/* if maxLen < 1, the applet crashes */

		if (maxLen < 1)

			maxLen = 1;

		ProactiveHandler proHdlr = ProactiveHandler.getTheHandler();

		proHdlr.initGetInput((byte)0, DCS_8_BIT_DATA, msg, (short)0, (short)(msg.length), minLen, maxLen);

		if (prefillVal != null && prefillVal.length > 0) {

			/* appendTLV() expects the first byte to be some header before the actual text.

			 * At first I thought it was the value's length, but turned out to only work for lengths under 8...

			 * In the end I reversed the value 4 from the first byte read by rspHdlr.copyValue() for

			 * TAG_TEXT_STRING fields. As long as we write 4 into the first byte, things just work out,

			 * apparently.

			 * Fucking well could have said so in the API docs, too; oh the brain damage, oh the hours wasted.

			 * This is the appendTLV() variant that writes one byte ahead of writing an array: */

			proHdlr.appendTLV((byte)(TAG_DEFAULT_TEXT), (byte)4, prefillVal, (short)0,

					  (short)(prefillVal.length));

		}

		proHdlr.send();

		return getResponse();

	}

	private void showError(short code) {

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

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

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

		showMsg(msg);

	}

	private void handleMenuResponseMain() {

		ProactiveResponseHandler rspHdlr = ProactiveResponseHandler.getTheHandler();

		switch (rspHdlr.getItemIdentifier()) {

		case 1: /* Show LU counter */

			showMsg(LUCounter);

			break;

		case 2: /* Change IMSI */

			byte prevIMSI_mi[] = readIMSI();

			byte prevIMSI_str[] = MobileIdentity.mi2str(prevIMSI_mi);

			promptIMSI(prevIMSI_str);

			break;

		}

	}

	private void promptIMSI(byte prevIMSI_str[])

	{

		byte newIMSI_str[] = prevIMSI_str;

		try {

			newIMSI_str = prompt(changeIMSI, newIMSI_str, (short)0, (short)15);

		} catch (Exception e) {

			showError((short)40);

			return;

		}

		if (newIMSI_str.length < 6 || newIMSI_str.length > 15

		    || !Bytes.isDigit(newIMSI_str)) {

			showMsg(invalidIMSI);

			return;

		}

		if (Bytes.equals(newIMSI_str, prevIMSI_str)) {

			showMsg(noChange);

			return;

		}

		byte mi[];

		try {

			/* The IMSI file should be 9 bytes long, even if the IMSI is shorter */

			mi = MobileIdentity.str2mi(newIMSI_str, MobileIdentity.MI_IMSI, (byte)9);

			writeIMSI(mi);

			showMsg(changed);

			refreshIMSI();

		} catch (Exception e) {

			showError((short)42);

		}

	}

	private byte[] readIMSI()

	{

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

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

		byte[] IMSI = new byte[9];

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

		return IMSI;

	}

	private void writeIMSI(byte mi[]) throws Exception

	{

		if (mi.length != 9)

			throw new Exception();

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

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

		gsmFile.updateBinary((short)0, mi, (short)0, (short)mi.length);

	}

	/*

	 * - command qualifiers for REFRESH,

	 *   ETSI TS 101 267 / 3GPP TS 11.14 chapter 12.6 "Command details":

	 *   '00' =SIM Initialization and Full File Change Notification;

	 *   '01' = File Change Notification;

	 *   '02' = SIM Initialization and File Change Notification;

	 *   '03' = SIM Initialization;

	 *   '04' = SIM Reset;

	 *   '05' to 'FF' = reserved values.

	 */

	public static final byte SIM_REFRESH_SIM_INIT_FULL_FILE_CHANGE = 0x00;

	public static final byte SIM_REFRESH_FILE_CHANGE = 0x01;

	public static final byte SIM_REFRESH_SIM_INIT_FILE_CHANGE = 0x02;

	public static final byte SIM_REFRESH_SIM_INIT = 0x03;

	public static final byte SIM_REFRESH_SIM_RESET = 0x04;

	/* Run the Proactive SIM REFRESH command for the FID_EF_IMSI. */

	private void refreshIMSI()

	{

		/* See ETSI TS 101 267 / 3GPP TS 11.14 section 6.4.7.1 "EF IMSI changing procedure":

		 * Valid qualifiers are SIM_REFRESH_SIM_INIT_FILE_CHANGE and SIM_REFRESH_SIM_INIT_FULL_FILE_CHANGE.

		 */

		ProactiveHandler proHdlr = ProactiveHandler.getTheHandler();

		proHdlr.init((byte)PRO_CMD_REFRESH, SIM_REFRESH_SIM_INIT_FULL_FILE_CHANGE, DEV_ID_ME);

		proHdlr.send();

	}

}