Documentation
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Overview ¶
Package tpms decodes TPMS (Tire Pressure Monitoring System) Sub-GHz bit-streams into the format-independent fields a pentester can trust: the Manchester line-decoded payload bytes, the 32-bit sensor ID, and CRC-8 validity. TPMS sensors beacon on 315 MHz (North America) and 433.92 MHz (Europe/Asia) and are a prime Flipper Sub-GHz target — they uniquely identify (and so let you track) a specific vehicle, and the wire format has no authentication.
Wrap-vs-native judgement ¶
Native. The hard, reusable part — recovering bytes from a Manchester-coded FSK/OOK bit-stream — is a public, deterministic transform (IEEE 802.3 and G.E. Thomas conventions). Operators bring a pre-demodulated bit-stream (rtl_433, a Flipper FSK Sub-GHz capture pre-extracted to bits, or Universal Radio Hacker) and decode offline, exactly as subghz_pocsag_decode does for paging.
What this package covers ¶
- Manchester line decoding under both conventions (IEEE 802.3: data 0 = "10", data 1 = "01"; G.E. Thomas: the inverse) at both bit alignments, auto-selecting the convention/alignment that yields the longest clean (no illegal "00"/"11" transition) decode — the correct one runs clean while the wrong one trips an illegal pair almost immediately.
- Leading-preamble tolerance: the alternating "0101…" preamble that most TPMS sensors send before the payload decodes to a run of data bits and is reported, not rejected.
- The decoded payload as hex, plus the 32-bit sensor ID — the first four payload bytes, which across virtually every TPMS family is the unique per-sensor identifier (the field-independent signal an operator uses to fingerprint or track a vehicle).
- CRC-8 validity probing against the polynomials TPMS sensors commonly use (0x07 CCITT, 0x2F, 0x13), reported as a confidence/alignment hint.
What this package does NOT cover (deliberately out of scope) ¶
- Manufacturer-specific pressure / temperature / status field interpretation: the byte offsets and scaling differ per family (Schrader, Toyota, Ford, Renault, Citroën, GM, Hyundai, …) and cannot be verified here without per-model captures. The raw decoded bytes are surfaced so an operator can apply the relevant rtl_433 model layout. Encoding this without sample data would risk a confidently-wrong reading — worse than none for a security tool.
- FSK/OOK demodulation (bring a pre-demodulated bit-stream).
- Differential-Manchester / biphase-mark variants used by a minority of sensors (standard Manchester is the common case here).
Index ¶
Constants ¶
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Variables ¶
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Functions ¶
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Types ¶
type Result ¶
type Result struct {
InputBits int `json:"input_bits"`
LineCoding string `json:"line_coding"`
BitAlignment int `json:"bit_alignment"`
DecodedBits int `json:"decoded_bits"`
DecodedBytes int `json:"decoded_bytes"`
DecodedHex string `json:"decoded_hex"`
SensorID string `json:"sensor_id,omitempty"`
SensorIDDecimal *uint32 `json:"sensor_id_decimal,omitempty"`
CRC8Matches []string `json:"crc8_matches,omitempty"`
Notes []string `json:"notes,omitempty"`
}
Result is the structured decode of a TPMS bit-stream.
Source Files