Measured entropy · SP800-90B-style estimate, pre-fold
0.0 bits
select an output size below
Output appears here. Nothing is stored or transmitted.
Pick once. It sets up everything after it.
Stays disconnected from the internet. Signs here; pairs with an online device to transact.
Stays connected to the internet. Transacts and scans data from the offline device.
Get the file to run offline, or on another device. Windows, Mac, Linux, iPhone, Android.
Native segwit, BIP-84. Sign offline, broadcast from a connected device.
Choose →ETH and any ERC-20, on Ethereum, Base, Arbitrum, Optimism and Polygon. BIP-44.
Choose →Encrypt any file or text. The encrypted file can live anywhere; its key files go somewhere else.
Choose →Read a code shown by gapbit on another device.
Choose →Mint a seed from measured physical entropy, with a live entropy estimate on screen. Then make its key files.
Begin →Restore from key files, import a BIP-39 seed, or watch an xpub.
Open →| estimator | mic | cam | jitter | pointer |
|---|
One file - the same one you are running. Use it online in your browser, or download it and run it offline. You pick Offline or Online each time it opens. The download is always the latest version.
Download, then double-click to open it in your browser. To use it offline: turn off Wi-Fi first, then open it and choose Offline.
Download, then double-click to open it in Safari or Chrome. To use it offline: turn off Wi-Fi first, then open it and choose Offline.
Download and open it in your browser. To use it offline: disconnect from the network first, then open it and choose Offline.
Open it in Safari, then Share → Add to Home Screen. To use it offline: turn on Airplane Mode, open it from the Home Screen, choose Offline.
Download and open it in Chrome. To use it offline: turn on Airplane Mode, open it, then choose Offline.
Confirm the exact file you are running, and that its built-in self-tests pass. It hashes this file's own bytes and checks the result against the published VERIFY.txt for you - so you can see at a glance whether it is the genuine, unmodified gapbit.
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 |
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.
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