simtrace2-pysniff

Python-based replacement for simtrace2-sniff — SIM card communication sniffer for Osmocom SIMtrace2 hardware (firmware in trace mode). It bundles the simtrace-analyser PWA (in frontend/) and an analysis server that both captures APDU traffic and serves that PWA.

Single dependency: PyUSB (libusb wrapper). No libosmocore, no libosmosim.

Features

APDU decoder (server-side, rendered by the PWA):

• Full APDU decode — CLA per ISO 7816-4 / ETSI coding (logical channel, secure messaging, command chaining), INS names from a spec table, SFI-aware P1/P2 for READ/UPDATE BINARY and record commands
• Status words — full ISO 7816-4 set plus UICC-specific values: 91XX (proactive command pending), 62F1/F2/F3, 63F1/F2 (more data), 9300 (SAT busy), 9850, 9862–64
• SIM Toolkit — SAT (GSM 11.14), CAT (TS 102 223) and USAT (TS 31.111) proactive commands with decoded qualifiers, TERMINAL RESPONSE, ENVELOPE (Menu Selection, Call Control, SMS-PP download…); tolerates known non-compliant legacy-card quirks and preserves unrecognized TLVs
• SMS TPDU — SMS-DELIVER/SUBMIT, SCTS timestamps, UDH information elements
• SCP80 OTA secured packets — SPI bits (ciphering, PoR requirement/mode, RC/CC/DS, counter), KIc/KID algorithm + key set, TAR, CNTR/PCNTR; Response Packet (PoR) decode on GET RESPONSE; optional client-side decryption of ciphered packets — paste the card's 3DES/AES key in the detail view to reveal the real CNTR and secured application data (the key stays in the browser, in-memory only; ciphered on-wire CNTR/PCNTR/RC are ciphertext and labeled as such); the secured application message is decoded as a stream of C-APDUs (SELECT, UPDATE BINARY, …) with full CLA/INS/P1/P2/Lc/Le breakdown — plaintext immediately, or after decryption for ciphered packets
• ATR parse (clock-rate conversion, Fi/Di, T-bitmask) and FCP/FCI TLV

simtrace-analyser PWA (frontend/):

• Trace view with Map/List modes — proactive, TERMINAL RESPONSE, ENVELOPE and AUTH commands get distinctive styling in map view
• Sessions with deep links (#session=N), PCAP import (.pcap/.pcapng/.cap), search and type filtering
• Installable PWA, dark theme, English/Russian UI

Prerequisites

• Python 3.9+
• PyUSB — pip install pyusb
• libusb — system library, present by default on Linux; on Windows the SIMtrace2 driver must be swapped (see USB Device Access)
• SIMtrace2 hardware running firmware in trace mode (VID 1d50, PID 60e3, USB class ff, subclass 01). For building and flashing trace firmware, see the upstream SIMtrace2 project.

No other dependencies. PCAP, GSMTAP, and hex dump output use only Python stdlib.

Install

git clone https://github.com/anttro/simtrace2-pysniff.git
cd simtrace2-pysniff
pip install pyusb

Or install the package into your environment:

pip install -e .
# then run: simtrace2-pysniff [opts]

Running

Two tools are provided:

Sniffer CLI (simtrace2-pysniff)

Captures SIMtrace2 traffic and writes it to stdout, GSMTAP (Wireshark), or PCAP files.

Startup script (Linux only)

./sniff-start.sh performs a pre-flight USB permission check (prints udev install instructions if the SIMtrace2 device is not writable) and then launches the Python module.

./sniff-start.sh
./sniff-start.sh --format timestamp
./sniff-start.sh --gsmtap 127.0.0.1:4729
./sniff-start.sh --pcap trace.pcap --format atr-time

OPTIONS can also be set via environment variables:

FORMAT=timestamp GSMTAP=127.0.0.1 ./sniff-start.sh

Analysis server + PWA (simtrace2-pysniff-server)

Stores captured APDU traffic in SQLite and serves it over HTTP, together with the bundled simtrace-analyser PWA (frontend/) on the same origin. Three capture modes:

# Listen for GSMTAP from simtrace2-pysniff (or original simtrace2-sniff):
simtrace2-pysniff-server --capture gsmtap

# Capture directly from SIMtrace2 hardware (no external tool needed):
simtrace2-pysniff-server --capture direct

# Browse/analyse existing captures without a capture backend:
simtrace2-pysniff-server --capture disabled

The server logs its capture liveness to stderr (each line timestamped with the local time): Capture started on begin, a periodic Capture alive: session=N messages=M bytes=B dropped=D heartbeat, and Capture stopped (or ERROR: capture thread stopped on error … if the capture thread died unexpectedly). A mis-framed or non-SIM GSMTAP datagram is dropped and counted (dropped) rather than silently killing the capture. The heartbeat interval defaults to 60 s and is tunable via --log-interval SECONDS.

The GSMTAP listener also accepts the sigrok-iso7816-stream decoder (https://github.com/anttro/sigrok_iso7816_stream) — an FX2-logic-analyzer passive SIM sniffer that emits the same GSMTAP-SIM format on UDP 4729. Its custom sub-types for RST/VCC line events (0x10/0x11, added for compatibility with that project) are decoded as RESET ASSERTED/DE-ASSERTED and VCC ON/OFF timeline markers, and a reset-assert or power-removal correctly invalidates the file-selection tracking. GSMTAP packets carrying the GSMTAP_FLAG_BAD_FCS desync flag (set by that decoder on mis-framed exchanges) are surfaced as a flagged/desynced entry in the capture timeline, so such artefacts are easy to spot when reviewing a capture rather than silently altering the decode.

Server options:

--host ADDR          HTTP bind address (default: 127.0.0.1)
--port PORT          HTTP server port (default: 8081)
--db FILE            SQLite database path (default: ~/.simtrace-analyser/sessions.db)
--capture MODE       gsmtap | direct | disabled  (default: gsmtap)
--gsmtap-port PORT   UDP port for the GSMTAP listener (default: 4729)
--web-dir PATH       PWA static files directory (default: <repo>/frontend)

Then open http://127.0.0.1:8081/ in a browser — the PWA is served by the server, so the UI and the API share an origin and no CORS/Private-Network-Access setup is involved. Use --web-dir PATH to serve a different PWA directory (default: <repo>/frontend).

Hosted PWA (landing page)

A standalone copy of the PWA is hosted at https://simtrace.atroshin.ru. It is a pure frontend: point it (Settings → Server URL) at a locally running simtrace2-pysniff-server.

Browser restriction: when the PWA is served from a public HTTPS host, reaching a local server (http://127.0.0.1:8081) requires two things: the server must send Access-Control-Allow-Private-Network: true (this server does), and the browser must be allowed to access the local network — in Chrome/Edge/Vivaldi: Site settings → Local network access → allow the site (or accept the permission prompt). Without the browser permission, the request to 127.0.0.1 is blocked before any preflight is sent.

Python module (cross-platform)

python -m simtrace2_pysniff
python -m simtrace2_pysniff --format timestamp --gsmtap 127.0.0.1:4729
python -m simtrace2_pysniff --pcap trace.pcap

If installed via pip install -e ., use the console script directly:

simtrace2-pysniff --format atr-time

USB Device Access

Linux

A udev rule is required for non-root USB access to the SIMtrace2 device.

sudo cp 70-simtrace2-pysniff.rules /etc/udev/rules.d/
sudo udevadm control --reload-rules
sudo udevadm trigger

Then reconnect the SIMtrace2 USB cable. The rule uses TAG+="uaccess" (systemd-logind ACL) — no group membership or world-writable permissions needed.

Windows

Windows does not ship a libusb-compatible driver for SIMtrace2. Use Zadig to replace the default driver:

1. Download and run Zadig
2. Plug in the SIMtrace2 device
3. Select it in the dropdown (VID 1D50, PID 60E3 — "Osmocom SIMtrace 2")
4. Choose WinUSB (or libusbK) as the replacement driver
5. Click Replace Driver (one-time operation)

After that, python -m simtrace2_pysniff works identically to Linux.

CLI Options

python -m simtrace2_pysniff [OPTIONS]

  --format, -f FORMAT       Output format (default: hex)
                            hex       — plain hex dump
                            timestamp — TPDU lines prefixed with [HH:MM:SS.mmm]
                            atr-time  — TPDU lines prefixed with [SSSS.mmm] from last ATR
  --gsmtap HOST[:PORT]      Send ATR/TPDU as GSMTAP over UDP (default port 4729)
  --pcap FILE               Write sniffed data to PCAP file for Wireshark
  --output, -o FILE         Write hex dump to file
  --no-stdout               Suppress hex dump to stdout
  --vendor HEX              USB vendor ID (default: 0x1d50)
  --product HEX             USB product ID (default: auto-detect)

Recovery options:
  --no-reconnect            Exit on USB disconnect instead of reconnecting
  --reconnect-delay-min SEC Minimum reconnect delay (default: 1.0)
  --reconnect-delay-max SEC Maximum reconnect delay cap (default: 30.0)
  --backoff-factor N        Exponential backoff multiplier (default: 1.5)
  --inactivity-timeout SEC  Reconnect after N seconds of silence (default: disabled)

Output Formats

• hex (default): plain hex dump — ATR: 3b 9e ..., TPDU: a0 a4 00 00 02 3f 00
• timestamp: TPDU lines prefixed with local time — [14:32:05.123] TPDU: a0 a4 00 00 02 3f 00
• atr-time: TPDU lines prefixed with seconds since last ATR — [0001.234] TPDU: a0 a4 00 00 02 3f 00

Non-TPDU messages (ATR, PPS, card state changes, Fi/Di) print identically in all formats.

• GSMTAP: ATR and APDU messages over UDP (port 4729) to Wireshark
• PCAP: ATR/TPDU messages as Ethernet/IP/UDP/GSMTAP packets, openable in Wireshark

Background / Daemon

SIGHUP is automatically ignored when stdin is not a terminal (i.e. run in background or via a pipe). Foreground terminal sessions still respond to SIGHUP normally.

To run persistently in the background with output to files:

nohup ./sniff-start.sh --output /tmp/sniff.log &> /tmp/sniff-err.log &
# or
FORMAT=timestamp nohup python -m simtrace2_pysniff --output /tmp/sniff.log &> /tmp/sniff-err.log &

Library Usage

from simtrace2_pysniff import SniffSession

session = SniffSession(inactivity_timeout=30.0)
for msg in session.iter_messages():
    print(f"{msg.type}: {msg.data.hex()}")

Recovery

The tool survives hardware resets, cable disconnects, and firmware hangs by default — it reconnects with exponential backoff (1s → 30s cap). Use --inactivity-timeout to also trigger reconnect on silent firmware hangs.

Related

• simtrace2 — the upstream SIMtrace2 hardware/firmware project that this tool sniffs from.