leviathan
45 lines
1.5 KiB
Markdown
45 lines
1.5 KiB
Markdown
# PSA (Peugeot/Citroën) Protocol
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**Rust module:** `src/protocols/psa.rs`
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**Reference:** `REFERENCES/ProtoPirate/protocols/psa.c`
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## Overview
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PSA uses Manchester at 250/500 µs symbol (125/250 µs sub-symbol for preamble). 128 bits total: key1 (64) + validation (16) + key2/rest (48); decode uses key1 + 16-bit validation. TEA decrypt/encrypt with fixed key schedules; mode 0x23 adds an XOR layer. Two modes: seed 0x23 (TEA + XOR), seed 0xF3/0x36 (TEA, BF2 key schedule).
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## Timing
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| Parameter | Value | Notes |
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|------------|--------|---------|
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| Symbol short | 250 µs | ±100 µs |
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| Symbol long | 500 µs | ±100 µs |
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| Preamble | 125/250 µs sub-symbols | |
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| Min bits | 128 | |
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## Encoding
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Manchester; preamble uses 125/250 µs; then 250/500 µs symbols. TEA encrypt; mode 0x23 adds XOR.
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## Frame Layout (128 bits)
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- key1: 64 bits
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- validation: 16 bits
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- key2/rest: 48 bits
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TEA decrypt key1 (and validation); mode 0x23: XOR with BF1 key schedule; mode 0x36: TEA with BF2 key schedule. Serial/button/counter extracted from decrypted key1.
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## Decoder Steps
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1. **WaitEdge** — Wait for edge/preamble.
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2. **CountPattern** — Count preamble pattern (125/250 µs).
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3. **DecodeManchester** — Manchester decode 128 bits; TEA decrypt; apply mode (0x23 XOR or 0x36); extract fields.
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4. **End** — End marker (e.g. 1000 µs); return decode.
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## Encoder
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Supported; preamble, Manchester 128 bits, TEA (+ XOR for 0x23).
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## Frequencies
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433.92 MHz.
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