ctf-rev

ctf-rev is a skill for Claude Code from cyberkaida/reverse-engineering-assistant. It costs 52 tokens per session (3,798 once invoked), scanned A, original, Apache-2.0.

A method for solving capture-the-flag reverse-engineering challenges by examining what a program expects, does, and validates.

In plain words
What is it for?
Use it for crackmes, binary puzzles, validation checks, algorithm recovery, and other CTF challenges involving program analysis.
Why use it?
It gives a structured way to understand unfamiliar or obfuscated programs when the goal is to recover a flag, key, or password.

Skill for Claude Code

Written for Claude Code: shipped in a Claude Code plugin.

Part of the ReVa plugin — 6 skills, 1 MCP server shipped together

Install

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.

agentmods
npx agentmods add skills/cyberkaida/reverse-engineering-assistant/ctf-rev
Any agent
npx skills add cyberkaida/reverse-engineering-assistant --skill ctf-rev
Clone the repo
git clone --depth 1 https://github.com/cyberkaida/reverse-engineering-assistant

Made for: Claude Code.

Or install ReVa, the plugin that ships this one along with the rest of its 6 skills, 1 MCP server.

Wrote 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.

agentmods badge for ctf-rev

README.md
[![agentmods](https://agentmods.dev/badge/skills/cyberkaida/reverse-engineering-assistant/ctf-rev.svg)](https://agentmods.dev/skills/cyberkaida/reverse-engineering-assistant/ctf-rev)
Your own site
<a href="https://agentmods.dev/skills/cyberkaida/reverse-engineering-assistant/ctf-rev"><img src="https://agentmods.dev/badge/skills/cyberkaida/reverse-engineering-assistant/ctf-rev.svg" alt="Measured on agentmods" height="20"></a>
Per session 52 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 3,798 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

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.

ModelPer sessionOnce invoked
Fable 5.1 $0.00052 $0.03798
Opus 5 $0.00026 $0.01899
Sonnet 5 $0.00010 $0.00760
Haiku 4.5 $0.00005 $0.00380

Measured 6d ago against content hash c9e14c95f6bd, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-05, from the pricing page.

Security

Grade A, and why

ctf-rev 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 6d 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.

ReVa/skills/ctf-rev/SKILL.md · 549 lines

How it starts

The opening of the file, as written. The whole thing — 549 lines — stays where its author put it; the contents beside it link to each section on GitHub.

CTF Reverse Engineering

Purpose

You are a CTF reverse engineering solver. Your goal is to understand what a program does and extract the flag/key/password through systematic analysis.

CTF reverse engineering is fundamentally about comprehension under constraints:

  • Limited time (competition pressure)
  • Unknown problem structure (what technique is being tested?)
  • Minimal documentation (that's the challenge!)
  • Goal-oriented (find the flag, not perfect understanding)

Unlike malware analysis or vulnerability research, CTF reversing tests your ability to:

  1. Quickly identify the core challenge (crypto? obfuscation? algorithm recovery?)
  2. Trace critical data flow (where does input go? how is it validated?)
  3. Recognize patterns (standard algorithms, common tricks)
  4. Adapt your approach (static vs dynamic, top-down vs bottom-up)

Conceptual Framework

The Three Questions

Every reverse engineering challenge boils down to answering:

1. What does the program EXPECT?

  • Input format (string, number, binary data?)
  • Input structure (length, format, encoding?)
  • Validation criteria (checks, comparisons, constraints?)

2. What does the program DO?

  • Transformation (encrypt, hash, encode, compute?)
  • Comparison (against hardcoded value, derived value?)
  • Algorithm (standard crypto, custom logic, mathematical?)

3. How do I REVERSE it?

  • Is the operation reversible? (encryption vs hashing)
  • Can I brute force? (keyspace size, performance)
  • Can I derive the answer? (solve equations, trace backwards)
  • Can I bypass? (patch, debug, manipulate state)

Understanding vs Solving

You don't need to understand everything - focus on what gets you to the flag:

Full Understanding (often unnecessary):

  • Every function's purpose
  • Complete program flow
  • All edge cases and error handling
  • Library implementation details

Sufficient Understanding (what you need):

  • Entry point to flag validation
  • Core transformation logic
  • Input-to-output relationship
  • Comparison or success criteria

Read the full file on GitHub · 549 lines

Files

What ships with it

1 file beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.

Changes

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.

  1. 6d ago First seen · 549 lines · 52 tokens per session scan A c9e14c95f6bd

Subscribe to this mod's changes

ctf-rev is a skill published in the GitHub repository cyberkaida/reverse-engineering-assistant (821 stars, last pushed 2d ago), licensed Apache-2.0. It adds 52 tokens to every session and 3,798 once invoked, about $0.0003 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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