From 60502eea04303ba2e7f9778d4f9e389ee1821316 Mon Sep 17 00:00:00 2001
From: Fabrice Rochette <45168870+mjfelis@users.noreply.github.com>
Date: Thu, 17 Sep 2026 00:17:33 +0200
Subject: [PATCH] feat: read the TAR of 03.48 response packets at the right
offset
A command packet (IEI 0x70) carries the TAR at offset 10, a response packet /
Proof of Receipt (IEI 0x71) at offset 6, right after RPL and RHL. Add
isResponsePacket, getResponsePacketTar, getPacketTar (IEI aware) and stripUdh.
Version 1.0.23.
---
pom.xml | 2 +-
.../mobiera/java/sim/tools/PacketUtil.java | 107 +++++++++++++++---
2 files changed, 91 insertions(+), 18 deletions(-)
diff --git a/pom.xml b/pom.xml
index d310ae0..6c91b07 100644
--- a/pom.xml
+++ b/pom.xml
@@ -4,7 +4,7 @@
com.mobiera.libs
common-sim
jar
- 1.0.22
+ 1.0.23
Common Sim
Common Sim
https://github.com/mobiera/common-sim
diff --git a/src/main/java/com/mobiera/java/sim/tools/PacketUtil.java b/src/main/java/com/mobiera/java/sim/tools/PacketUtil.java
index 5ecbec9..b024bbe 100644
--- a/src/main/java/com/mobiera/java/sim/tools/PacketUtil.java
+++ b/src/main/java/com/mobiera/java/sim/tools/PacketUtil.java
@@ -1,43 +1,116 @@
package com.mobiera.java.sim.tools;
+/**
+ * Helpers for GSM 03.48 / ETSI TS 102 225 secured packets carried in SMS user data.
+ *
+ * Both packet kinds start with a 3 byte user data header: UDHL (02), IEI, IEDL (00).
+ * IEI 0x70 is a command packet, IEI 0x71 a response packet (Proof of Receipt).
+ *
+ *
+ * command packet : UDH(3) CPL(2) CHL(1) SPI(2) KIc(1) KID(1) TAR(3) CNTR(5) PCNTR(1) ...
+ * response packet : UDH(3) RPL(2) RHL(1) TAR(3) CNTR(5) PCNTR(1) STATUS(1) ...
+ *
+ */
public class PacketUtil {
private static int MIN_PACKET_SIZE = 10;
-
+
+ public static final byte IEI_COMMAND_PACKET = (byte) 0x70;
+ public static final byte IEI_RESPONSE_PACKET = (byte) 0x71;
+
+ public static final int UDH_LENGTH = 3;
+ public static final int COMMAND_PACKET_TAR_OFFSET = UDH_LENGTH + 2 + 1 + 2 + 1 + 1; // 10
+ public static final int RESPONSE_PACKET_TAR_OFFSET = UDH_LENGTH + 2 + 1; // 6
+ public static final int TAR_LENGTH = 3;
+
// check if looks a command packet
// 027100000E0A00000000000000000000016101
// 027100000B0A0000000000000000000A
-
+
+ /**
+ * True when the message starts with a 03.48 user data header, either command (0x70)
+ * or response (0x71) packet. Kept for backward compatibility: despite its name it
+ * accepts both kinds.
+ */
public static boolean isCommandPacket(byte[] msg) {
-
- if (msg.length >= MIN_PACKET_SIZE) {
+
+ if (msg != null && msg.length >= MIN_PACKET_SIZE) {
// binary msg
- if ( (msg[0] == (byte)0x02) && ( (msg[1] == (byte)0x71) || (msg[1] == (byte)0x70) ) && (msg[2] == (byte)0x00)) {
+ if ( (msg[0] == (byte)0x02) && ( (msg[1] == IEI_RESPONSE_PACKET) || (msg[1] == IEI_COMMAND_PACKET) ) && (msg[2] == (byte)0x00)) {
// looks like a packet
-
+
return true;
-
+
}
}
-
+
return false;
}
-
+
+ /**
+ * True when the message is a 03.48 response packet (Proof of Receipt), IEI 0x71.
+ */
+ public static boolean isResponsePacket(byte[] msg) {
+ return isCommandPacket(msg) && msg[1] == IEI_RESPONSE_PACKET;
+ }
+
+ /**
+ * TAR of a command packet (offset 10, after the security parameters). Do not use on a
+ * response packet, see {@link #getPacketTar(byte[])}.
+ */
public static byte[] getCommandPacketTar(byte[] msg) {
-
- byte[] binTar = new byte[3];
- System.arraycopy(msg, 10, binTar, 0, 3);
+
+ byte[] binTar = new byte[TAR_LENGTH];
+ System.arraycopy(msg, COMMAND_PACKET_TAR_OFFSET, binTar, 0, TAR_LENGTH);
+ return binTar;
+
+ }
+
+ /**
+ * TAR of a response packet (offset 6, right after RPL and RHL).
+ */
+ public static byte[] getResponsePacketTar(byte[] msg) {
+
+ byte[] binTar = new byte[TAR_LENGTH];
+ System.arraycopy(msg, RESPONSE_PACKET_TAR_OFFSET, binTar, 0, TAR_LENGTH);
return binTar;
-
+
}
-
+
+ /**
+ * TAR of either packet kind, chosen from the UDH IEI. Returns null when the message is
+ * not a packet or is too short to hold a TAR.
+ */
+ public static byte[] getPacketTar(byte[] msg) {
+
+ if (!isCommandPacket(msg)) return null;
+
+ int offset = (msg[1] == IEI_RESPONSE_PACKET) ? RESPONSE_PACKET_TAR_OFFSET : COMMAND_PACKET_TAR_OFFSET;
+ if (msg.length < offset + TAR_LENGTH) return null;
+
+ byte[] binTar = new byte[TAR_LENGTH];
+ System.arraycopy(msg, offset, binTar, 0, TAR_LENGTH);
+ return binTar;
+ }
+
+ /**
+ * Packet without its user data header, i.e. starting at CPL or RPL. Returns the
+ * message itself when it does not carry a 03.48 UDH.
+ */
+ public static byte[] stripUdh(byte[] msg) {
+ if (!isCommandPacket(msg)) return msg;
+ byte[] out = new byte[msg.length - UDH_LENGTH];
+ System.arraycopy(msg, UDH_LENGTH, out, 0, out.length);
+ return out;
+ }
+
public static boolean isEncrypted(byte[] msg) {
-
+
if (((msg[6]) & (msg[7])) != 0x00) {
return true;
}
return false;
}
-
-
+
+
}