KaraZajac
754af4134a
Brings KAT to 32 protocol decoders. Ported from the ProtoPirate reference and the D4C1-Labs/Flipper-ARF firmware: ProtoPirate (8): Kia V7, Ford V1, Ford V2, Ford V3, Chrysler V0, Honda Static, Honda V1, Land Rover V0. Flipper-ARF (6): Toyota, Land Rover RKE, Mazda Siemens, BMW CAS4, Porsche Cayenne, PSA2. Each decoder is gated (CRC / checksum / fixed markers / frame structure) so it cannot false-match existing protocols; every previously-decoding IMPORTS capture decodes unchanged. Real-capture decodes added for Ford V3 (LDV T80), Honda Static (Honda), Toyota (Camry NRZ variant), and PSA2 (Groupe PSA, serial 0x99EB25); the rest are validated by encode/decode round-trip and synthetic-frame tests. Also fixes a debug-only underflow panic in keeloq_common::keeloq_decrypt (15 - r underflowed; now wrapping_sub to match the reference's unsigned wrap; release behavior unchanged). Adds per-protocol docs, updates the README protocol table, capture metadata (encoding / RF / encryption), make-suggestion mapping, and CHANGELOG. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01JEfaKqzB3T4qsrybwfEi73
65 lines
2.6 KiB
Markdown
65 lines
2.6 KiB
Markdown
---
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layout: default
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---
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# BMW CAS4 Protocol
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**Rust module:** `src/protocols/bmw_cas4.rs`
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**Reference:** `Flipper-ARF lib/subghz/protocols/bmw_cas4.c`
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## Overview
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BMW CAS4 uses Manchester encoding at 500/1000 µs. 64 bits (8 bytes), AM/OOK. The CAS4 rolling cipher's
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manufacturer key is not available, so the encrypted portion is left as-is — the frame is only framed and
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validated, not decrypted. Emission is gated on two fixed marker bytes (`byte[0] == 0x30` and
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`byte[6] == 0xC5`), which makes the protocol specific and prevents false matches.
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The Manchester decoder uses Flipper's `manchester_decoder.h` transition table, with polarity
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`level ? Low : High` (the same mapping as Ford V0 / common).
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## Timing
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| Parameter | Value | Notes |
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|----------------|---------|-----------------------------|
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| Short | 500 µs | ±150 µs (te_delta) |
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| Long | 1000 µs | ±150 µs |
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| Preamble pulse | 300–700 µs | |
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| Gap | ≥1800 µs | separates preamble from data |
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| Min bits | 64 | 8 bytes |
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| Preamble | ≥10 pulses | |
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## Frame Layout (64 bits / 8 bytes)
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- **byte 0:** fixed marker `0x30`
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- **bytes 1–3:** serial (24-bit)
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- **byte 5:** counter
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- **byte 6:** fixed marker `0xC5`
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- **byte 7:** button
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The CAS4 rolling cipher is left undecrypted; the two markers serve as the integrity gate.
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## RF
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- **Encoding:** Manchester (Flipper table, polarity `level ? Low : High`)
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- **RF modulation:** AM/OOK
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- **Encryption:** CAS4 rolling cipher left undecrypted (no manufacturer key); gated on fixed markers `0x30`/`0xC5`
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- **Frequencies:** 433.92 MHz only
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## Decoder Steps
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1. **Reset** — begin on a HIGH preamble pulse within the 300–700 µs window.
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2. **Preamble** — count preamble pulses; a long LOW gap (≥1800 µs) with ≥10 pulses enters Data.
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3. **Data** — Manchester-decode 64 bits MSB-first; at the 64th bit, require `byte[0]==0x30 && byte[6]==0xC5`, build the signal on success, and reset. An out-of-range pulse aborts.
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## Encoder
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Not supported (the reference encoder is a non-functional stub: `yield` returns reset, `deserialize`
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returns error). Decode-only.
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## Validation
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Verified by a synthetic-frame check (no local capture available): a unit test Manchester-encodes a frame
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by driving the decoder's own transition table (the Flipper table is differential, so there is no
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fixed per-bit pattern), confirms it decodes with the right serial/counter/button, and confirms a frame
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with wrong marker bytes is rejected.
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