pentest-ctf-crypto

pentest-ctf-crypto is a skill for Claude Code, Codex from jd-opensource/JoySafeter. It costs 26 tokens per session (213 once invoked), scanned A, original, Apache-2.0.

A guide to cryptography challenges in capture-the-flag (CTF) security competitions, including ciphers, hashes, and weak encryption.

In plain words
What is it for?
Recognizing encodings, cracking classical ciphers, checking weak RSA keys, analyzing hashes, and solving cryptography math problems.
Why use it?
It helps identify how challenge data was protected and choose an appropriate way to analyze it.

Skill for Claude CodeCodex

Written for no agent in particular: nothing here depends on one.

Good fit Recognizing encodings, cracking classical ciphers, checking weak RSA keys, analyzing hashes, and solving cryptography math problems.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/jd-opensource/joysafeter/pentest-ctf-crypto
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.

Any agent
npx skills add jd-opensource/JoySafeter --skill pentest-ctf-crypto
Clone the repo
git clone --depth 1 https://github.com/jd-opensource/JoySafeter

Made for: Claude Code, Codex.

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 pentest-ctf-crypto

README.md
[![agentmods](https://agentmods.dev/badge/skills/jd-opensource/joysafeter/pentest-ctf-crypto.svg)](https://agentmods.dev/skills/jd-opensource/joysafeter/pentest-ctf-crypto)
Your own site
<a href="https://agentmods.dev/skills/jd-opensource/joysafeter/pentest-ctf-crypto"><img src="https://agentmods.dev/badge/skills/jd-opensource/joysafeter/pentest-ctf-crypto.svg" alt="Measured on agentmods" height="20"></a>
Per session 26 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 213 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe. Third-party audits
  • NVIDIA SkillSpector pass 7 Sept 2026
How audits are shown
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 $0.00026 $0.00213
Opus 5 $0.00013 $0.00106
Sonnet 5 $0.00005 $0.00043
Haiku 4.5 $0.00003 $0.00021

Measured 8d ago against content hash 61b82234be9c, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-07, from the pricing page.

Security

Grade A, and why

pentest-ctf-crypto 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 8d 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.

skills/pentest-ctf-crypto/SKILL.md · 21 lines

What it actually says

Pentest CTF Crypto

Purpose

Analyze and break cryptographic implementations, including classical ciphers, RSA weak keys, and hash extensions.

Core Workflow

  1. Cipher Identification: Identify the type of encryption or encoding used (e.g., Base64, Caesar, RSA).
  2. Classical Cracking: Brute-force or analyze frequency for classical ciphers using ciphey or online tools.
  3. RSA Attacks: Check for common RSA weaknesses (small e, small factors) using RsaCtfTool.
  4. Hash Analysis: Identify hash types and attempt cracking or length extension attacks using hashcat or hashpump.
  5. Math/Primes: Solve mathematical problems related to cryptography using sagemath.

References

  • references/tools.md
  • references/workflows.md
Files

What ships with it

2 files 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. 8d ago First seen · 21 lines · 26 tokens per session scan A 61b82234be9c

Subscribe to this mod's changes

pentest-ctf-crypto is a skill published in the GitHub repository jd-opensource/JoySafeter (306 stars, last pushed 3d ago), licensed Apache-2.0. It adds 26 tokens to every session and 213 once invoked, about $0.0001 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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