Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx skills add trilwu/secskills --skill reversing-network-protocolsgit clone --depth 1 https://github.com/trilwu/secskillsWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/trilwu/secskills/reversing-network-protocols)<a href="https://agentmods.dev/skills/trilwu/secskills/reversing-network-protocols"><img src="https://agentmods.dev/badge/skills/trilwu/secskills/reversing-network-protocols/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/trilwu/secskills/reversing-network-protocols"><img src="https://agentmods.dev/badge/skills/trilwu/secskills/reversing-network-protocols.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- NVIDIA SkillSpector pass
What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00094 | $0.01310 |
| Opus 5 | $0.00047 | $0.00655 |
| Sonnet 5 | $0.00019 | $0.00262 |
| Haiku 4.5 | $0.00009 | $0.00131 |
Grade A, and why
reversing-network-protocols scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 9d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 112 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Reversing Network Protocols
An undocumented binary protocol is reverse-engineered from two sides at once: the wire, which shows you the bytes that actually flow, and the client, which shows you the code that produced them. Neither alone is enough — the capture tells you what varies, the client tells you why — and the deliverable is a parser precise enough to decode, replay, and eventually fuzz the protocol.
When to Use
- A proprietary or custom TCP/UDP protocol with no public specification
- Traffic Wireshark displays as raw
Databytes because no dissector matches - Game, IoT, industrial, or C2 protocols you must decode from captures plus the client binary
- Building a Wireshark dissector, a Kaitai Struct spec, or a scapy layer to parse and replay a protocol
When NOT to Use
- A known/structured protocol — Protobuf or gRPC specifically is
attacking-grpc-protobuf; standard protocols have dissectors already. - Defensive PCAP investigation — hunting, IOC extraction, incident triage —
is
analyzing-network-traffic. - Reversing the client binary itself (disassembly, decompilation) is
analyzing-binaries; do that in service of the protocol, then structure it here. - Identifying or breaking the crypto once you find the protocol is encrypted
—
reviewing-cryptography.
Work Both Sides
From the capture, establish structure by comparing many messages:
- Framing — how a message knows where it ends: a length prefix (a field that tracks payload size across messages), a delimiter, or fixed-size records. Finding the length field is usually the first breakthrough.
- Constants and magic — bytes identical across every message mark headers, version fields, or type tags.
- Opcode / message type — a small field that correlates with different message shapes; group captures by it.
- Counters and sequence numbers — fields that increment monotonically.
- Checksums — a trailing field that changes unpredictably with the payload; test CRC variants against the message body.
- TLV — many custom protocols are type-length-value triplets once you see the pattern.
- Endianness — confirm from a known length: does a 260-byte message carry
04 01or01 04?
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 9d ago First seen · 112 lines · 94 tokens per session scan A a796b4083597
reversing-network-protocols is a skill published in the GitHub repository trilwu/secskills (137 stars, last pushed 4d ago), licensed MIT. It adds 94 tokens to every session and 1,310 once invoked, about $0.0005 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.
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