Cuvex – Offline Encryption & Sovereign Signing Device Cuvex is a sovereign encryption and signing device designed to operate fully offline for all cryptographic operations, while offering carefully constrained interfaces for usability and system updates. All sensitive processes, seed encryption, decryption and transaction signing, are performed without any internet connectivity and under explicit user verification. Seed phrase encryption & recovery Cuvex allows users to create and manage a secure seed phrase recovery process for any wallet. Seed phrases are encrypted using AES-256 GCM Encrypted secrets (cryptograms) are stored externally on passive NFC cards No private keys or decrypted data are stored on the device This patented approach eliminates the risks associated with storing seed phrase backups on paper or steel, while maintaining a fully offline security model. NFC cards for cryptograms and transactions Cuvex includes multiple NFC cards with clearly separated roles: Cryptogram cardsUsed exclusively to store encrypted seed phrases. These cards are passive and only allow read/write operations. They do not execute code, expose secrets, or establish active communication channels. Transaction cardA dedicated NFC card used to transfer unsigned PSBT transactions from the smartphone app to the device. This card can be reused for an unlimited number of transactions. Three colored cryptogram cards are included, enabling flexible multisignature setups such as 3-of-3, 4-of-4, or up to 6-of-6 schemes. Physical entropy for seed generation Cuvex supports sovereign seed generation using physical entropy. A set of four colored dice is included to allow seed creation using the Dice & Coin standard, eliminating reliance on opaque software-based random number generators. The user actively participates in the entropy process, ensuring high-quality randomness and full transparency from the very first step of wallet creation. Watch-Only wallet management Wallet management is performed through the Cuvex Smartphone App (Watch-Only Wallet). No private keys are ever present in the app No user accounts are required No personal data is collected Advanced privacy features such as Coin Control, UTXO labeling, and freezing are available, allowing precise and privacy-preserving wallet management regardless of the user’s technical level. Double AirGap PSBT transaction signing Cuvex implements a Double AirGap PSBT signing process: The Watch-Only app prepares an unsigned PSBT transaction The PSBT is transferred to the device via the dedicated NFC transaction card (first air gap) After verification on the device screen, the encrypted seed cryptogram card is presented (second air gap) The transaction is signed fully offline All sensitive data is erased from device memory after signing The device never stores private keys and can manage an unlimited number of wallets, as secrets are never persisted internally. Firmware updates and secure boot Firmware updates are performed via Bluetooth exclusively in the bootloader, not during normal device operation. The bootloader verifies the RSA signature of the firmware before installation Unsigned or altered firmware is automatically rejected Bluetooth is never active during encryption, decryption, or signing operations This design allows secure updates while preserving a strict offline model for all critical cryptographic functions.
