Keep is a FROST (Flexible Round-Optimized Schnorr Threshold Signatures) threshold signing app and dedicated Nostr event signer for Android.

It allows users to hold FROST key shares on their phone and sign Nostr events without any single device ever holding the full private key. Keep implements the NIP-55 Android Signer protocol and NIP-46 remote signing, so any compatible Nostr client can request signatures directly.

Keep keeps private key material segregated from client apps through NIP-55 and NIP-46, with per-app permissions, background signing, and multiple account support. It splits keys into FROST threshold shares (2-of-3, 3-of-5, etc.) so that no single device ever holds the complete private key.

Features:

FROST threshold signing (2-of-3, 3-of-5, etc.)
NIP-55 Android Signer protocol (intents + content provider)
NIP-46 remote signing (bunker service)
Import and export FROST shares via QR code or text
Import existing nsec keys
Multiple account support
Per-app signing permissions and policies
Signing history and audit log
Biometric and PIN authentication
Hardware-backed key storage (Android Keystore)
Kill switch for emergency key deletion
SOCKS proxy support (Tor)
NIP-44 encryption and decryption
Background signing with configurable rate limits
Certificate pinning for relay connections
Encrypted backup and restore
Bitcoin wallet descriptor coordination (multisig)