CTF ZIP Archive Key Recovery
zhaoxuya520/reverse-skill
Recovers internal keys from legacy ZipCrypto-protected ZIP archives in CTF challenges through a known-plaintext method, instead of brute force.
Reference the ZIP/ZIP64/PKWARE APPNOTE archive container format.
MITAuto-check passed
Install Zip Format
$ npx skills add adamhathcock/sharpcompress --skill zip-format -a claude-codeProject install by default; add -g for ~/.claude/skills/.
$ gh skill install adamhathcock/sharpcompress zip-format --agent claude-codeProject scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).
$ git clone --depth 1 https://github.com/adamhathcock/sharpcompress.git skills-src && mkdir -p .claude/skills && cp -r skills-src/.agents/skills/zip-format .claude/skills/zip-format && rm -rf skills-srcUse ~/.claude/skills/ instead of .claude/skills for a personal install. The folder must contain SKILL.md.
Claude Code skills documentation · loads skills from .claude/skills/
Install the "zip-format" agent skill from https://github.com/adamhathcock/sharpcompress/tree/master/.agents/skills/zip-format into .claude/skills/zip-format/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "zip-format", then confirm the skill loads.Claude Code copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$skill-installer install https://github.com/adamhathcock/sharpcompress/tree/master/.agents/skills/zip-formatType this inside Codex. $skill-installer <name> installs a curated skill from openai/skills. The installer writes to $CODEX_HOME/skills (default ~/.codex/skills). Restart Codex if the skill does not show up.
$ npx skills add adamhathcock/sharpcompress --skill zip-format -a codexProject install goes to .agents/skills/; add -g for ~/.codex/skills/.
$ gh skill install adamhathcock/sharpcompress zip-format --agent codexProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/adamhathcock/sharpcompress.git skills-src && mkdir -p .agents/skills && cp -r skills-src/.agents/skills/zip-format .agents/skills/zip-format && rm -rf skills-srcUse ~/.agents/skills/ instead of .agents/skills for a personal install.
Codex skills documentation · loads skills from .agents/skills/
Install the "zip-format" agent skill from https://github.com/adamhathcock/sharpcompress/tree/master/.agents/skills/zip-format into .agents/skills/zip-format/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "zip-format", then confirm the skill loads.Codex copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ npx skills add adamhathcock/sharpcompress --skill zip-format -a cursorProject install goes to .agents/skills/; add -g for ~/.cursor/skills/.
$ gh skill install adamhathcock/sharpcompress zip-format --agent cursorProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/adamhathcock/sharpcompress.git skills-src && mkdir -p .cursor/skills && cp -r skills-src/.agents/skills/zip-format .cursor/skills/zip-format && rm -rf skills-srcUse ~/.cursor/skills/ instead of .cursor/skills for a personal install.
Cursor skills documentation · loads skills from .cursor/skills/, .agents/skills/, .claude/skills/, .codex/skills/
Install the "zip-format" agent skill from https://github.com/adamhathcock/sharpcompress/tree/master/.agents/skills/zip-format into .cursor/skills/zip-format/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "zip-format", then confirm the skill loads.Cursor copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ gemini skills install https://github.com/adamhathcock/sharpcompress.git --path .agents/skills/zip-format--scope user (default) or --scope workspace; --path is the subfolder of the repo that holds the skill; --consent skips the security confirmation prompt.
$ npx skills add adamhathcock/sharpcompress --skill zip-format -a gemini-cliProject install goes to .agents/skills/; add -g for ~/.gemini/skills/.
$ gh skill install adamhathcock/sharpcompress zip-format --agent gemini-cliProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/adamhathcock/sharpcompress.git skills-src && mkdir -p .gemini/skills && cp -r skills-src/.agents/skills/zip-format .gemini/skills/zip-format && rm -rf skills-srcUse ~/.gemini/skills/ instead of .gemini/skills for a personal install, then run /skills reload.
Gemini CLI skills documentation · loads skills from .gemini/skills/, .agents/skills/
Install the "zip-format" agent skill from https://github.com/adamhathcock/sharpcompress/tree/master/.agents/skills/zip-format into .gemini/skills/zip-format/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "zip-format", then confirm the skill loads.Gemini CLI copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ gh skill install adamhathcock/sharpcompress zip-formatInstalls for Copilot at project scope by default; add --scope user for a personal install. Preview a skill first with gh skill preview. Needs GitHub CLI 2.90.0 or later (public preview).
$ npx skills add adamhathcock/sharpcompress --skill zip-format -a github-copilotProject install goes to .agents/skills/; add -g for ~/.copilot/skills/.
$ git clone --depth 1 https://github.com/adamhathcock/sharpcompress.git skills-src && mkdir -p .github/skills && cp -r skills-src/.agents/skills/zip-format .github/skills/zip-format && rm -rf skills-srcUse ~/.copilot/skills/ instead of .github/skills for a personal install. Commit .github/skills so cloud agent and code review can use it.
GitHub Copilot skills documentation · loads skills from .github/skills/, .claude/skills/, .agents/skills/
Install the "zip-format" agent skill from https://github.com/adamhathcock/sharpcompress/tree/master/.agents/skills/zip-format into .github/skills/zip-format/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "zip-format", then confirm the skill loads.GitHub Copilot copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
$ npx skills add adamhathcock/sharpcompress --skill zip-format -a opencodeOpenCode documents no install command of its own. Project install goes to .agents/skills/; add -g for ~/.config/opencode/skills/.
$ gh skill install adamhathcock/sharpcompress zip-format --agent opencodeProject scope by default (.agents/skills/); add --scope user for a personal install.
$ git clone --depth 1 https://github.com/adamhathcock/sharpcompress.git skills-src && mkdir -p .opencode/skills && cp -r skills-src/.agents/skills/zip-format .opencode/skills/zip-format && rm -rf skills-srcUse ~/.config/opencode/skills/ instead of .opencode/skills for a personal install.
OpenCode skills documentation · loads skills from .opencode/skills/, .claude/skills/, .agents/skills/
Install the "zip-format" agent skill from https://github.com/adamhathcock/sharpcompress/tree/master/.agents/skills/zip-format into .opencode/skills/zip-format/ in this project. Copy the whole folder (SKILL.md and every file beside it), keep the folder name "zip-format", then confirm the skill loads.OpenCode copies the folder itself, the same result as the manual copy. Check what it changed before you commit it.
Facts
- Skill name
zip-format- GitHub stars
- 2.6k
- Token cost
- ~613 tokens
- SKILL.md length
- 231 words
- Files
- 2 (incl. references)
- Skills in repo
- 5
- Repo updated
- First seen
- Licence
- MIT
At a glance
Reference the ZIP/ZIP64/PKWARE APPNOTE archive container format.
- Works in 5 steps: Identify which layer is involved: header… → Open the relevant section in… → For parsing changes, cross-check sync… → …
- An AI agent needs to answer questions
- SKILL.md covers Reference and Workflow
- Reaches pkware.cachefly.net
What it does
Zip Format is an agent skill from adamhathcock/sharpcompress. Reference the ZIP/ZIP64/PKWARE APPNOTE archive container format. Use when an AI agent needs to answer questions or make code changes involving ZIP local headers, central directory records, EOCD/Zip64 records, data descriptors, general purpose bit flags, compression method IDs, extra fields, encryption markers, split archives, or SharpCompress Zip parsing and writing behavior.
Its SKILL.md is about 610 tokens, which your agent loads only when the skill is triggered. The skill folder holds 2 other files, including reference files (for example `references/zip-format.md`).
The repository describes itself as: SharpCompress is a fully managed C library to deal with many compression types and formats. The licence is MIT.
When your agent uses it
- An AI agent needs to answer questions
- Make code changes involving ZIP local headers
- Central directory records
- EOCD/Zip64 records
Example prompts
- “/zip-format”
Workflow steps
5 steps, taken from the first numbered list in SKILL.md.
- Identify which layer is involved: header discovery, local file headers, central directory headers, EOCD/Zip64 records, data descriptors…
- Open the relevant section in references/zip-format.md and use the source-file pointers before changing code.
- For parsing changes, cross-check sync and async header readers: ZipHeaderFactory.cs, ZipHeaderFactory.Async.cs…
- For writer changes, verify local header, post-data descriptor, central directory, Zip64, and sync/async paths together.
- For support claims, keep unsupported features explicit: central directory encryption, strong encryption records, XZ writing, non-standard…
What it can do on your machine
Read from SKILL.md and the folder at commit 2cba09e. It shows what the files ask for, not the result of running them.
Tool permissions
Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.
From allowed-tools in the SKILL.md frontmatter.
Runs code
No scripts in the folder and no shell commands in SKILL.md.
From the folder's file list and the shell code blocks in SKILL.md.
Network
Hosts in commands or code, which the agent is likely to contact:
pkware.cachefly.net
From URLs in SKILL.md, links to its own repository left out.
Credentials
Names no API keys, tokens, secrets or passwords.
From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.
Context cost
Zip Format loads about 613 tokens when it runs, and up to ~5.4k if it reads all its reference files. Until then it costs about 97 tokens; SKILL.md has 231 words of instructions outside code blocks.
Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.
Safety
Auto-check passed
The automated check found no risky patterns in SKILL.md.
Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.
SKILL.md
The full file from adamhathcock/sharpcompress at commit 2cba09e, republished under its MIT licence (© adamhathcock). 231 words, ~613 tokens.
Download SKILL.mdSave it as
.claude/skills/zip-format/SKILL.md (or your agent's skills folder). This skill also uses 1 other file; get the full folder from GitHub.- name
- zip-format
- description
- Reference the ZIP/ZIP64/PKWARE APPNOTE archive container format. Use when an AI agent needs to answer questions or make code changes involving ZIP local headers, central directory records, EOCD/Zip64 records, data descriptors, general purpose bit flags, compression method IDs, extra fields, encryption markers, split archives, or SharpCompress Zip parsing and writing behavior.
Zip Format
Use this skill for ZIP container-format work. It provides a local, SharpCompress-oriented reference for PKWARE APPNOTE ZIP records, ZIP64, compression method IDs, extra fields, and the current SharpCompress Zip implementation.
Reference
- Read references/zip-format.md when the task depends on ZIP binary layout, record signatures, local vs central directory metadata, data descriptor rules, Zip64 sentinel values, extra field parsing, compression method IDs, encryption markers, split archive handling, or current SharpCompress Zip support boundaries.
- Treat the reference as an implementation guide, not a standards replacement. It summarizes PKWARE APPNOTE 6.3.10 from
https://pkware.cachefly.net/webdocs/casestudies/APPNOTE.TXTand documents SharpCompress-specific behavior and limitations. - Prefer the SharpCompress support matrix in the reference over generic ZIP assumptions when changing code. ZIP is highly extensible, and SharpCompress intentionally supports only selected records, methods, and extra fields.
Workflow
- Identify which layer is involved: header discovery, local file headers, central directory headers, EOCD/Zip64 records, data descriptors, extra fields, compression methods, encryption, reader/archive/writer API behavior, or tests.
- Open the relevant section in
references/zip-format.mdand use the source-file pointers before changing code. - For parsing changes, cross-check sync and async header readers:
ZipHeaderFactory.cs,ZipHeaderFactory.Async.cs,SeekableZipHeaderFactory.cs,StreamingZipHeaderFactory.cs,ZipFileEntry.cs,LocalEntryHeader.cs, andDirectoryEntryHeader.cs. - For writer changes, verify local header, post-data descriptor, central directory, Zip64, and sync/async paths together.
- For support claims, keep unsupported features explicit: central directory encryption, strong encryption records, XZ writing, non-standard compression methods, broad extra-field semantics, and non-seekable Zip64 writing.
© adamhathcock, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file
Files
SKILL.md and 1 other file (references) in .agents/skills/zip-format of adamhathcock/sharpcompress.
- SKILL.md
- references/zip-format.md
Open the folder on GitHubat commit 2cba09e
Compare with similar skills
Zip Format next to the 5 skills that share the most tags, products or categories with it. Stars are the repository's; “used in” counts other GitHub owners with a copy.
| Skill | Stars | Used in | Tokens | Auto-check | Licence | Repo updated |
|---|---|---|---|---|---|---|
| Zip Format this skilladamhathcock/sharpcompress | 2.6k | — | ~613 | Automated safety check: Pass | MIT | |
| CTF ZIP Archive Key Recoveryzhaoxuya520/reverse-skill | 40k | 1 repos | ~1.5k | Automated safety check: Pass | MIT | |
| Apple Containersickn33/agentic-awesome-skills | 47k | 1 repos | ~2.5k | Automated safety check: Pass | Apache-2.0 | |
| Container Security Hardeningsickn33/agentic-awesome-skills | 47k | 1 repos | ~1k | Automated safety check: Notes | MIT | |
| Container Queriesthedaviddias/Front-End-Checklist | 74k | — | ~526 | Automated safety check: Pass | MIT | |
| CSS Containmentthedaviddias/Front-End-Checklist | 74k | — | ~512 | Automated safety check: Pass | MIT |
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Questions about Zip Format
What does Zip Format do?
Reference the ZIP/ZIP64/PKWARE APPNOTE archive container format. Zip Format is an agent skill from adamhathcock/sharpcompress. Reference the ZIP/ZIP64/PKWARE APPNOTE archive container format.
When should I use Zip Format?
Zip Format fits situations like: an AI agent needs to answer questions; make code changes involving ZIP local headers; central directory records; EOCD/Zip64 records.
How do I install Zip Format in Claude Code?
Run `npx skills add adamhathcock/sharpcompress --skill zip-format -a claude-code`. Or copy the skill folder (.agents/skills/zip-format in adamhathcock/sharpcompress) into .claude/skills/zip-format in your project. Claude Code loads it when a task matches its description.
How do I install Zip Format in Codex?
Run `npx skills add adamhathcock/sharpcompress --skill zip-format -a codex`. Or copy the skill folder (.agents/skills/zip-format in adamhathcock/sharpcompress) into .agents/skills/zip-format in your project. Codex loads it when a task matches its description.
Can I use Zip Format in Cursor, Gemini CLI or GitHub Copilot?
Cursor, Gemini CLI, GitHub Copilot and OpenCode also load SKILL.md folders. With the skills CLI, run `npx skills add adamhathcock/sharpcompress --skill zip-format -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/zip-format, .gemini/skills/zip-format, .github/skills/zip-format and .opencode/skills/zip-format in your project.
What does Zip Format need to run?
SKILL.md names no scripts, command-line tools or credentials: Zip Format is instructions for the agent only.
Does Zip Format access the network?
SKILL.md names 1 domain. In commands or code: pkware.cachefly.net; the agent is likely to contact it when it follows the instructions. This is read from the text; nothing was executed.
Is Zip Format safe to install?
Our automated static check of SKILL.md found no risky patterns, such as piping downloads into a shell, reading credential files or hidden Unicode. It is not a guarantee. Review the folder before installing.
What licence does Zip Format use?
Zip Format is published under the MIT licence (the repository's licence). It allows redistribution, so the full SKILL.md is shown on this page.
How many tokens does Zip Format use?
About 613 tokens (SKILL.md is roughly 2.5k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full. Its references folder adds about 4.8k tokens, read only when the agent opens those files.
What are the alternatives to Zip Format?
Skills that share tags, products or a category with Zip Format: CTF ZIP Archive Key Recovery (zhaoxuya520/reverse-skill, 40k stars), Apple Container (sickn33/agentic-awesome-skills, 47k stars), Container Security Hardening (sickn33/agentic-awesome-skills, 47k stars) and Container Queries (thedaviddias/Front-End-Checklist, 74k stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.
Who maintains Zip Format?
adamhathcock (a GitHub user) maintains it in adamhathcock/sharpcompress, which has 2,587 GitHub stars. The repository holds 5 skills in this directory. The repository was last updated on October 8, 2026.
Source: adamhathcock/sharpcompress on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.