Keep: FROST Nostr Signer

Keep: FROST Nostr Signer is an open-source Android application for FROST threshold signing and Nostr event signing. It allows a phone to hold a FROST key share and sign Nostr events without placing the complete private key on one device. The app is intended for people who use Nostr and need a dedicated signer that separates event signing from a Nostr client.

The app supports threshold arrangements such as 2-of-3 and 3-of-5 signing. It implements the NIP-55 Android Signer protocol, allowing compatible Nostr clients to request signatures from the Android app. It also supports NIP-46 remote signing through a bunker service.

FROST shares can be imported and exported using QR codes or text, and the app supports multiple accounts. Per-app signing permissions and policies control which applications can request signatures, while biometric and PIN authentication protect access. Key storage uses the Android Keystore, and the app includes encrypted backup and restore, NIP-44 encryption and decryption, and SOCKS proxy support for Tor.

In the Security & Privacy category, Keep fits Android devices that are used as signing tools rather than general-purpose Nostr clients. MirrorNest distributes the official Android build directly from its own storage and scans it for malware before publishing. The listing provides access to the mirrored open-source application while retaining its focus on threshold keys, controlled signing requests, and protected account data.