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
77 lines
3.6 KiB
Markdown
77 lines
3.6 KiB
Markdown
---
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layout: default
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---
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# PSA2 Protocol
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**Rust module:** `src/protocols/psa2.rs`
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**Reference:** `Flipper-ARF lib/subghz/protocols/psa2.c`
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## Overview
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PSA2 (Peugeot/Citroën — internal name "PSA OLD") is the OLDER PSA variant, distinct from KAT's existing
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`psa` (modified-TEA/XEA) decoder. Manchester encoding: 250/500 µs symbol (Pattern 1, standard rate) or
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125/250 µs (Pattern 2, half rate), using the canonical Flipper `manchester_advance` table. 128-bit frame
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= key1 (64 bits) + key2/validation word: the decoder collects 64 bits → key1, then 16 more (to 80 bits)
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→ the 16-bit validation field / key2_low.
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Crypto: TEA (Tiny Encryption Algorithm) with a dual brute-force fallback (BF1 0x23000000–0x24000000, BF2
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0xF3000000–0xF4000000) and a mode23/mode36 selector, validated via a nibble checksum.
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**Performance:** the live decoder only ever runs the cheap O(1) mode23 XOR path
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(`direct_xor_decrypt`) per frame — it NEVER runs the TEA brute force. The bounded TEA brute force
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(`decrypt_full`, ~16.7M iters per range) is ported faithfully but is reserved for a deferred-decrypt UI
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action, mirroring the C exactly. Beyond the C's nibble-checksum gate, KAT adds two false-positive
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suppressors required by its feed-all-decoders model: a `key2_high` precondition and a valid-button check
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(PSA2 buttons are Lock=0, Unlock=1, Trunk=2 only). Emission is gated strictly on a successful,
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field-bearing mode23 decrypt.
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## Timing
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| Parameter | Value | Notes |
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|----------------|--------|-----------------------------|
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| Short (P1) | 250 µs | ±100 µs (te_delta) |
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| Long (P1) | 500 µs | ±100 µs |
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| Short (P2) | 125 µs | ±50 µs (half rate) |
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| Long (P2) | 250 µs | ±50 µs |
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| End marker | 1000 µs (P1) / 500 µs (P2) | |
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| Min bits | 128 | key1 (64) + validation (16) collected |
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| Preamble | >0x46 pairs (P1) / >0x45 (P2) | |
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## Frame Layout (128 bits = key1 64-bit + key2/validation)
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The decoder collects 64 bits → key1, then 16 bits → the validation field (key2_low). After the mode23 XOR
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decrypt (fields from `extract_fields_mode23`):
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- **serial:** `(buf[2]<<16) | (buf[3]<<8) | buf[4]` (24-bit)
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- **button:** `buf[8] & 0xF` — Lock=0, Unlock=1, Trunk=2
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- **counter:** `(buf[5]<<8) | buf[6]` (16-bit)
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- **crc:** `buf[7]`
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`data` = `(key1_high << 32) | key1_low` (64 bits).
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## RF
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- **Encoding:** Manchester (canonical Flipper table; standard 250/500 µs or half-rate 125/250 µs)
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- **RF modulation:** AM (OOK)
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- **Encryption:** TEA + nibble-checksum-gated mode23 XOR path; brute-force fallback reserved for offline decrypt
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- **Frequencies:** 433.92 MHz
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## Decoder Steps
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1. **WaitEdge (State0)** — detect the preamble rate (250 µs → Pattern 1, 125 µs → Pattern 2).
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2. **CountPattern250/125 (State1/3)** — count preamble pulses past the threshold, then a long pulse enters the Manchester decode state.
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3. **DecodeManchester250/125 (State2/4)** — Manchester-decode to 80 bits (key1 + validation), detect end-of-packet, then `finalize_frame` runs the cheap mode23 XOR gate and emits only on a successful field-bearing decrypt.
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## Encoder
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Supported (mode23 path). Increments the counter, builds key1/validation via `encode_mode23` (inverse XOR
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stage + nibble checksum), then emits an 80-pair preamble, a sync, 64 key1 bits + 16 validation bits
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MSB-first, and an end burst.
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## Validation
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Decodes REAL IMPORTS captures (IMPORTS/GROUPE PSA, serial `0x99EB25`). Unit tests also cover the TEA
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round trip, the mode23 encode→decode round trip, the nibble checksum vs. the reference, and the emitted
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Manchester frame length.
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