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"He did the mash. He did the monster mash."
Encryption that doesn't bite. Monstermash wraps the battle-tested NaCl (libsodium) cryptography in a friendly CLI, a clean Python API, and an MCP server — so developers, engineers, and now AI agents can encrypt things correctly without touching a single cryptographic knob.
1️⃣ version: 2.1.0 · ✍️ author: Mitchell Lisle
Why Monstermash?
- 🔒 Safe by default — built on NaCl's
Box(Curve25519 + XSalsa20-Poly1305). No hand-rolled crypto, no caller-managed nonces, no footguns. - 🪄 Decrypt with just your private key — the sender's public key rides inside the ciphertext (the "Mashed Envelope"), so the recipient needs nothing extra.
- 🧰 One tool, three surfaces — the same guarantees from the CLI, the Python library, and an optional MCP server for LLMs.
- 🗝️ Profiles, not key-juggling — store keypairs once (mode
0600, just like your SSH keys) and reference them by name. - 🚨 Tamper-evident — authenticated encryption fails loudly; a corrupted or wrong-key ciphertext raises, it never returns garbage.
Install
pip install monstermash
Want the MCP server for AI agents? Grab the optional extra:
pip install "monstermash[mcp]"
Quickstart
1. Generate a keypair
monstermash generate
-----------------
Private Key (keep it secret, keep it safe)
a715a3d11d0f9c13de3bd6d390e36ba4e3322f4f2e4f1a13a54ba85be606de87
Public Key (you can share this one)
01765c67f451f3175f53bbe11d69d73a36d45074da935271473b4a1c460e3d79
-----------------
2. Save it as a profile (optional, but nice)
Profiles live in ~/.monstermashcfg and are written with owner-only (0600) permissions.
monstermash configure \
--profile default \
--private-key a715a3d11d0f9c13de3bd6d390e36ba4e3322f4f2e4f1a13a54ba85be606de87 \
--public-key 01765c67f451f3175f53bbe11d69d73a36d45074da935271473b4a1c460e3d79
3. Encrypt
monstermash encrypt --profile default --data "hello world"
Or pass keys explicitly, or encrypt a whole file:
monstermash encrypt \
--private-key a715a3d11d0f9c13de3bd6d390e36ba4e3322f4f2e4f1a13a54ba85be606de87 \
--public-key 03ab4b8a77456729678a8022c2bfe22f64ed2db72692903e5f69e4a92649e646 \
--file ./secret-plans.txt
4. Decrypt
monstermash decrypt \
--private-key 91c7b2534454587a3330537bce60056e9da9a9bf75d32507152f49e85514970d \
--data 01765c67f451f3175f53bbe11d69d73a36d45074da935271473b4a1c460e3d797bee92fa7ff1216eb5324b247fd41cce283adbcc4df92baacfea27765360a7c0feb226cccc1538c0397783003d0283d2841d2a
The --profile flag works here too — no public key needed, it's baked into the ciphertext.
How it works
Monstermash owns no cryptographic primitives — it leans entirely on NaCl. What it adds is ergonomics:
plaintext ──▶ NaCl Box (Curve25519 + XSalsa20-Poly1305) ──▶ [ sender public key │ nonce │ MAC │ ciphertext ] ──▶ hex
└──────────── the "Mashed Envelope" ────────────┘
Because the sender's public key travels inside the envelope, the recipient decrypts with only their
private key. See docs/domain/cryptography.md for the full domain
model and design decisions.
MCP Server
Monstermash ships an optional Model Context Protocol server so an LLM can do real encryption natively — without ever handling raw private keys.
Security model: tool arguments flow into the model's context, so private keys never cross the
boundary. The model works by profile name (à la ssh-agent); the server reads the key from disk
locally. Set a default with MONSTERMASH_MCP_DEFAULT_PROFILE.
Run it over stdio:
monstermash-mcp
Register it with an MCP client (e.g. Claude Desktop):
{
"mcpServers": {
"monstermash": {
"command": "monstermash-mcp"
}
}
}
Tools
| Tool | Description |
|---|---|
generate_keypair |
Generate a keypair, store it under a profile, and return only the public key. |
encrypt |
Encrypt text using a profile's keys. Recipient defaults to the profile; target a stored contact with recipient, or pass a raw public_key. |
decrypt |
Decrypt a ciphertext using a profile's private key. |
configure |
Import an existing keypair under a named profile. |
add_contact |
Store a shared public key under a name (a contact); usable as an encrypt recipient, never able to decrypt. |
list_profiles |
List profile names and public keys — private keys are never returned. |
License
See the repository for license details.
1 maintainer
Metadata
1 maintainer
Release files for monstermash 2.1.0
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Total release size: 210.7 kB
Release files / monstermash-2.1.0.tar.gz
| Download URL | monstermash-2.1.0.tar.gz |
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| Tags | Source |
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Release files / monstermash-2.1.0-py3-none-any.whl
| Download URL | monstermash-2.1.0-py3-none-any.whl |
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| Tags | Python 3 |
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