gap // bit

HOW WILL YOU USE THIS?

This decides how the app behaves - coins, files and secrets alike. Pick once; it sets up everything after it.

■ AIR-GAPPED

FOR SAVINGS & CRITICAL SECRETS

Coins, files and secrets you cannot afford to lose. Air-gap is not a mode inside this online build - a file that can reach the network cannot promise it never will. It is a separate signer with no network code at all.

This build is the online one. For true air-gap, get the dedicated signer: it has no way to connect, you verify it once, and you run it on a device with the radios off. Tap to download it.

A separate file: gapbit-signer-airgapped.html
No network code (connect-src none)
Cannot update itself
Create keys, sign, receive - all offline
Not this online file

Get the air-gapped signer →

□ STANDARD

FOR SPENDING & EVERYDAY FILES

Behaves like a normal wallet. Check your balance, receive, send, broadcast and encrypt files - online or off, whenever you want.

Nothing is enforced. You'll be warned before each step that connects, and then it is your call. Your keys can end up on a machine that goes online, and if that machine is ever compromised they can be taken.

You decide, every time
Balance, send and broadcast here
Encrypt files here
Use a second device or don't

Choose →

₿ BITCOIN

Native segwit, BIP-84. Sign offline, broadcast from a connected device.

Choose →

Ξ ETHEREUM & ERC-20

ETH and any ERC-20, on Ethereum, Base, Arbitrum, Optimism and Polygon. BIP-44.

Choose →

▣ FILES & SECRETS

Encrypt any file or text. The encrypted file can live anywhere; its key files go somewhere else.

Choose →

⬚ SCAN

Read a code shown by gapbit on another device. Keys and vaults can be saved here as files; a signed transaction can be broadcast.

Choose →

CREATE NEW WALLET

Mint a seed from measured physical entropy, with a live entropy estimate on screen. Then make its key files.

Begin →

OPEN EXISTING WALLET

Restore from key files, import a BIP-39 seed, or watch an xpub.

Open →

← back to chain

Physical sources

enables jitter · clock · pointer instantly; asks for mic + camera

MICROPHONE

- H∞

0 b/s idle

CAMERA

- H∞

0 b/s idle

JITTER

- H∞

0 b/s idle

POINTER

- H∞

0 b/s idle

CLOCK

- H∞

0 b/s idle

Measured entropy · SP800-90B-style estimate, pre-fold

0.0 bits

select an output size below

Key size

Output appears here. Nothing is stored or transmitted.

Already have a wallet? Import seed · Restore encrypted file · Watch-only (xpub)

SP800-90B-style estimate · per source

estimator	mic	cam	jitter	pointer

How the entropy stays honest

Min-entropy is measured on raw source bits before the fold, as the minimum of eight SP800-90B estimators - a structured source collapses toward zero and is caught.
The gapbit φ fold (φ · e · plastic · Zeckendorf, all public constants) braids the sources and stirs the pool. It conditions only - it adds no entropy, and hides no constant.
Release requires ≥ 2× the output size in measured bits; entropy is then spent, never reused.
Combined mode XORs the result with the OS generator: provably at least as strong as the standard tool, plus independent physical sources you can watch being measured.
Extraction is a Toeplitz/LHL step (ε = 2⁻⁶⁴) with a deterministic public seed; finalization is HKDF-SHA-512. In physical-only mode nothing in the key path touches the OS generator.

pool stirs 0

Hold the other screen steady in frame.

SELF-TESTS HKDF BIP-39 BIP-39 seed extractor seed

file hash: not verified

gapbit.com

PACKAGES & LICENSES

Everything bundled into this file, what each one does here, and its licence. All third-party code is MIT. Nothing is fetched at runtime.

PACKAGE	USED FOR	LICENCE
@scure/btc-signer	Bitcoin addresses, PSBT construction and signing	MIT, Patricio Palladino and Paul Miller
@scure/bip32	BIP-32 hierarchical key derivation	MIT, Patricio Palladino and Paul Miller
@scure/bip39	BIP-39 mnemonic encoding and seed derivation	MIT, Patricio Palladino and Paul Miller
@scure/base	bech32, base58 and base64 encoding	MIT, Paul Miller
@noble/curves	secp256k1 signing for Bitcoin and Ethereum	MIT, Paul Miller
@noble/hashes	SHA-256, SHA-512, keccak256, HMAC	MIT, Paul Miller
hash-wasm	Argon2id, the key derivation for encrypted backups	MIT, Dani Biro
qrcode	drawing QR codes	MIT, Ryan Day
jsQR	reading QR codes from the camera	MIT, Cosmo Wolfe
WebCrypto	HKDF, PBKDF2, AES-GCM and SHA, built into the browser	browser built-in, not bundled

What is not from a package. The entropy pipeline and its SP800-90B estimators, the Shamir implementation over GF(256), the encrypted vault container and the Ethereum transaction encoding are hand-written for this file. They are tested, including byte-for-byte against ethers.js, but no one has paid for a formal audit. Nothing about secp256k1 is hand-rolled.

gapbit itself is MIT too. Copyright (c) 2026 gapbit. Free to use, copy, modify and sell, personally or commercially, at no cost and with no permission needed. The full text is below. Verify this file against VERIFY.txt before trusting it with anything.
No warranty. gapbit is provided as is and has not been formally audited. It holds no keys and cannot recover anything: if you lose your seed words or key files, the funds are gone permanently. You use it at your own risk and the full responsibility is yours.

MIT License

Copyright (c) 2026 gapbit

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.

gap // bit

HOW WILL YOU USE THIS?

■ AIR-GAPPED

□ STANDARD

₿ BITCOIN

Ξ ETHEREUM & ERC-20

▣ FILES & SECRETS

⬚ SCAN

CREATE NEW WALLET

OPEN EXISTING WALLET

Physical sources

How the entropy stays honest

Create wallet

Import existing seed

Watch-only

Protect a file or a secret

Recover a file or a secret

Your recovery words

Scan

Back up the wallet

Receive

Send

Sign transaction (PSBT)

Broadcast

Receive · Ethereum

Send · Ethereum / ERC-20

Sign transaction (Ethereum)

Broadcast · Ethereum

Key files

Are you sure?

PACKAGES & LICENSES