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UDS / ISO-TP Primer

A short, practical introduction. Expanded in M6; the essentials up front:

  • CAN carries up to 8 data bytes per classic frame.
  • ISO-TP (ISO 15765-2) segments larger messages across frames:
    • Single Frame — payload fits in one CAN frame.
    • First Frame + Consecutive Frames — a longer message, paced by
    • Flow Control — the receiver dictates block size and separation time.
  • UDS (ISO 14229) is the diagnostic request/response protocol on top. Key services used in this lab:
    • 0x10 DiagnosticSessionControl — switch session (default / extended / programming)
    • 0x3E TesterPresent — keep the session alive (S3 timeout)
    • 0x22 / 0x2E ReadDataByIdentifier / WriteDataByIdentifier
    • 0x27 SecurityAccess — seed/key challenge to unlock protected services
    • 0x23 ReadMemoryByAddress — read memory once unlocked
  • A negative response uses SID 0x7F plus a negative response code (NRC); leaking too much detail in NRCs is itself a weakness (see VULNERABILITIES.md).