Coldstar is an air-gapped, non-custodial self-custody system for the Solana blockchain. It allows a user to turn any standard USB drive into a cold wallet: a private key is encrypted at rest on the USB using AES-256-GCM with Argon2id key derivation, and is decrypted only in volatile memory (RAM) for the microseconds required to sign a transaction, after which it is wiped. The private key is never written to disk and never exposed to a networked machine. Coldstar is distributed as an open-source command-line tool, installable via pip, and as an application on the Solana Mobile Seeker dApp Store. COLD is the community and governance token of the Coldstar protocol.