KaraZajac
48ee413c9b
New protocols (from ProtoPirate): - Mazda V0: 433MHz, pair-based decoding, XOR deobfuscation - Mitsubishi V0: 868MHz, PWM, bit negation + XOR unscrambling - Porsche Touareg: 433/868MHz, sync preamble, 24-bit rotate cipher - Fiat V1 (Magneti Marelli BSI): 433MHz, auto-detected timing variants Protocol fixes aligned with ProtoPirate reference: - Kia V1: Fix Manchester level mapping (inverted convention), off-by-one bit count, CRC4 simplified to 7 bytes + offset 1 - Kia V2: Fix CRC byte layout (was double-counting nibbles), off-by-one bit count, preamble short-HIGH handling - Fiat V0: Fix endbyte transform (remove (<<1)|1), standard Manchester encoder (was differential), 7 btn bits (was 6), gap path fallback - PSA: Fix modified TEA (XTEA-like dynamic key selection), XOR decrypt byte mapping, critical key2_low construction bug, encoder polarity and preamble, add key1_high nibble validation, dual preamble patterns - Ford V0: Add calculate_checksum (sums all serial+count bytes) for encoder Kia V6 encoder ported: - Forward AES-128 (SubBytes, ShiftRows, MixColumns, encrypt) - encrypt_payload: build plaintext, AES encrypt, pack into 3 parts - Two-pass Manchester upload (640 + 38 preamble pairs) - fx_field extraction stored in DecodedSignal.extra for encode roundtrip Updated README, protocol docs, and version bump to 1.2.0.
78 lines
3.1 KiB
Markdown
78 lines
3.1 KiB
Markdown
---
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layout: default
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---
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# PSA (Peugeot/Citroen) 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 encoding with dual preamble pattern support. 128 bits total: key1 (64) + validation (16) + key2/rest (48). Modified TEA (XTEA-like) with dynamic key selection (`key[sum & 3]` and `key[(sum >> 11) & 3]`). Two decode modes: mode 0x23 (direct XOR decrypt with checksum validation) and mode 0x36 (TEA with BF1/BF2 key schedules). Brute-force decryption for mode 0x36 is deferred/partial.
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## Timing
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| Parameter | Value | Notes |
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|-------------|--------|---------|
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| Symbol short | 250 us | +/-100 us |
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| Symbol long | 500 us | +/-100 us |
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| Preamble P1 | 250 us sub-symbols | Pattern 1 |
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| Preamble P2 | 125 us sub-symbols | Pattern 2 |
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| End marker | 1000 us (P1), 500 us (P2) | |
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| Min bits | 128 | |
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## Dual Preamble Patterns
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- **Pattern 1 (250 us):** Preamble uses 250 us sub-symbols; Manchester decode at 250/500 us. Threshold: 70+ transitions.
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- **Pattern 2 (125 us):** Preamble uses 125 us sub-symbols; Manchester decode at 125/250 us. Threshold: 69+ transitions.
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Pattern type is auto-detected from the first preamble pulse duration.
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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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## Encryption
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### Modified TEA (XTEA-like)
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Uses dynamic key word selection per round:
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- Encrypt: `k_idx1 = sum & 3`, then `sum += DELTA`, then `k_idx2 = (sum >> 11) & 3`
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- Decrypt: `k_idx2 = (sum >> 11) & 3`, then `sum -= DELTA`, then `k_idx1 = sum & 3`
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- Round function: `(key[k_idx] + sum) ^ (((v >> 5) ^ (v << 4)) + v)`
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### Mode 0x23 (Direct XOR)
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1. Setup byte buffer from key1/key2 (little-endian unpack).
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2. Calculate checksum over buffer[2..8] (nibble sum * 16).
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3. Validate: `(checksum ^ key2_high_byte) & 0xF0 == 0`.
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4. XOR decrypt using `psa_copy_reverse` byte reordering.
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5. Extract: serial (24-bit), counter (16-bit), button (4-bit), CRC.
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### Mode 0x36 (TEA Brute-Force)
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Direct TEA decrypt attempted with BF1 and BF2 key schedules. Full brute-force (16M iterations per schedule) is available in ProtoPirate but not fully ported to KAT.
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Key schedules:
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- BF1: `[0x4A434915, 0xD6743C2B, 0x1F29D308, 0xE6B79A64]`
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- BF2: `[0x4039C240, 0xEDA92CAB, 0x4306C02A, 0x02192A04]`
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## Decoder Steps
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1. **WaitEdge (State0)** -- Detect preamble pattern type from first HIGH pulse (250 us -> Pattern 1, 125 us -> Pattern 2).
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2. **CountPattern250 (State1)** -- Count 250 us preamble pairs; on long pulse with count > 70, transition to Manchester decode.
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3. **DecodeManchester250 (State2)** -- Manchester decode at 250/500 us. End on 1000 us marker or 121+ bits.
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4. **CountPattern125 (State3)** -- Count 125 us preamble pairs; on 250 us pulse with count >= 69, transition to Manchester decode.
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5. **DecodeManchester125 (State4)** -- Manchester decode at 125/250 us. End on 500 us marker or 121+ bits.
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## Encoder
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Supported (mode 0x23 only). XOR encrypt, then modified TEA encrypt with BF1 key schedule. Preamble: 70 cycles of 125/125 us + 250/250 us sync. Manchester encoded key1 (64 bits) + validation (16 bits). End marker: 1000 us LOW.
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## Frequencies
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433.92 MHz.
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