Luthen

Luthen is a command-line tool that encrypts a file with age and splits the encryption key into SLIP-39 mnemonic shares, so that a chosen number of shares is needed to recover the file. It runs entirely offline. A web app does the same in the browser; its seal zips have the same contents as the CLI's seal folders.

Install

Download the binary for your platform, plus SHA256SUMS, from the Releases page. On Linux and macOS, make it executable with chmod +x.

Run from source

Install the Bun version in .bun-version, then:

bun install
bun src/cli/main.ts --help

Run with Node or Bun

If you already have Node 22 or newer, or Bun, download luthen.mjs (about 150 KB instead of the ~100 MB binaries, which embed a JavaScript runtime) plus SHA256SUMS from Releases, verify it like a binary (gh attestation verify luthen.mjs --repo ROODAY/luthen), and run:

node luthen.mjs --help
bun luthen.mjs --help

Verify a release

Check the checksum, then the build provenance attestation:

sha256sum -c SHA256SUMS --ignore-missing
gh attestation verify luthen-linux-x64 --repo ROODAY/luthen

luthen.mjs and luthen.html (the web app) are listed in SHA256SUMS and attested too.

On macOS, check the checksum with shasum -a 256 -c SHA256SUMS --ignore-missing. On Windows (PowerShell), run Get-FileHash <file> -Algorithm SHA256 and compare the hash with the matching line in SHA256SUMS.

To rebuild it yourself, check out the release tag, install the Bun version in .bun-version, and run bash scripts/build.sh dist. The resulting dist/SHA256SUMS should match the published one.

Web app

https://rooday.com/luthen does the same as the CLI in your browser, with everything computed locally. For offline use, download luthen.html from Releases and open it. Its seal zips have the same contents as the CLI's bundle folders.

Verify the downloaded file like a binary:

sha256sum -c SHA256SUMS --ignore-missing
gh attestation verify luthen.html --repo ROODAY/luthen

To check the hosted page, compare the output of this with the luthen.html line in SHA256SUMS:

curl -s https://rooday.com/luthen/ | sha256sum

Develop with bun run dev:web; build luthen.html with bun run build:web.

Usage

Split a file into 3 shares (one bundle directory each), any 2 of which recover it:

luthen seal secrets.txt --shares 3 --threshold 2 --out bundle

Recover it (omit share files to be prompted for the words):

luthen open bundle/share-1/secrets.txt.age -s bundle/share-1/share.txt -s bundle/share-2/share.txt -o secrets.txt

Check that shares can decrypt a bundle without writing the plaintext:

luthen verify bundle/share-1/secrets.txt.age -s bundle/share-1/share.txt -s bundle/share-2/share.txt

Recovery never requires Luthen: see RECOVERY.md in any bundle.

Security notes

• Files Luthen writes (bundle files and open output) are created readable only by you (mode 0600, directories 0700). This has no effect on Windows.
• Memory hygiene is best effort. JavaScript cannot guarantee that secrets are wiped from memory: the age passphrase is an immutable string that stays until garbage collected, and the runtime may keep copies. Byte buffers holding the secret and the plaintext are zeroed where practical.
• The web app's page CSP forbids all network requests. Browser memory hygiene is best effort. Browser extensions can read page contents, so use a clean profile or open the downloaded luthen.html offline.

Status

Pre-release. The interface and file formats may change without notice.

Licensing

Luthen is source-available under the PolyForm Noncommercial License 1.0.0. It is not OSI open source. It is free for personal and noncommercial use. Commercial rights are reserved to the owner. See LICENSE. Release binaries also bundle third-party code under its own licenses (MIT, BSD-3-Clause); see THIRD_PARTY_NOTICES.txt attached to each release.

Contributions

Pull requests are not accepted. Bug reports are welcome.