Sign anything

Ed25519key: —

Paste text, drop a file, or type. FallSignature signs it with your local Ed25519 private key. The signed bundle carries the content, the signature, your public key, a timestamp, and the algorithm. Anyone with the bundle can verify it. Nobody but you can forge it.

Content to sign

Drop a file here, or click to choose · the file bytes will be loaded as content

Quine mode · embed the signature inside the signed content itself (self-referencing seal)

Verify a bundle

Ed25519

Paste a signed bundle JSON, or a quine-mode signed file. FallSignature checks the signature against the embedded public key. No network, no server, no trust anchors — just math.

Signed bundle (JSON or quine-stamped text)

Drop a .sig.json or quine-stamped file here, or click to load

Your keys

local only

Your Ed25519 keypair is generated by the browser's Web Crypto API and stored in IndexedDB on this device. The private key never leaves. If you clear browser data or switch devices, you'll need to export first and import there.

Public key (base64) · safe to share no key yet

Public key fingerprint (SHA-256, first 16 hex) —

Created —

Manage

Generate keypair

Creates a fresh Ed25519 keypair. Replaces the existing one. Export first if you want to keep the old identity.

Export keypair (JSON)

Downloads both keys as JWK JSON. Keep this file offline — anyone with it can sign as you.

Import keypair

Restore from a previous export. Overwrites the current keypair.

Copy public key

The base64-encoded public key. Share this so others can verify your signatures.

Wipe keypair

Deletes the keypair from this browser. Irreversible unless you exported.

Privacy check. Open your browser's Network tab and click every button on this page. You'll see zero requests. Keys are generated, stored, and used entirely inside your browser.

About FallSignature

A private content-signing tool. One HTML file, runs entirely in your browser. Ed25519 keypair generated via the Web Crypto API and stored in IndexedDB. Private key never leaves the device. No accounts, no servers, no tracking.

The signed bundle format

JSON schema {
  "algorithm": "Ed25519",
  "content": "<the signed text/bytes as string or base64>",
  "encoding": "utf8" | "base64",
  "signature": "<base64 Ed25519 signature>",
  "pubkey": "<base64 public key>",
  "timestamp": "<ISO 8601>",
  "issuer": "FallSignature"
}

Quine mode

In quine mode, the signature is stamped at the end of the file itself. The content is signed with a placeholder in place of the signature, then the signature is inserted where the placeholder was. The whole file — stamp included — is self-verifying.

Quine stamp format (appended to content) —— FALLSIGNATURE ◊·κ=1 ——
algorithm: Ed25519
pubkey: <base64>
timestamp: <ISO 8601>
signature: <base64>
—— END SIGNATURE ——

The tool signs the content with signature: %SIGNATURE_PLACEHOLDER%, then substitutes the real signature in. Verification reverses the substitution before checking.

Browser support

Requires Web Crypto API support for Ed25519 (Chrome 113+, Edge 113+, Safari 17+, Firefox 130+). Older browsers see a compatibility notice.

License

MIT · Copyright 2026 AI-Native Solutions · private and local.
github.com/sjgant80-hub/fallsignature

◊·κ=1