The Problem: NFTs Are High-Value Digital Assets With Software-Level Security
Non-fungible tokens can represent significant financial value — from digital art and collectibles to real-world asset tokenization, event tickets, and intellectual property rights Yet the private keys controlling these assets are typically stored in software wallets vulnerable to phishing attacks, malware, browser exploits, and social engineering A single compromised key means the irreversible loss of every NFT in the associated wallet Despite the availability of general-purpose hardware wallets and cold wallets for cryptocurrency, no purpose-built solution existed for NFT security that addresses the unique requirements of non-fungible token management
The Innovation: Multi-Signature Authorisation Inside Tamper-Resistant Hardware
Granted by the European Patent Office on 5 August 2026 and registered as a Unitary Patent, EP 4 060 540 B1 protects a signing device — such as a Cryptnox smart card with a CC EAL6+ secure element — whose private key (or the seed from which its keys are derived) never leaves the secure element, and which signs a transaction only after an authorisation protocol has been completed inside that secure element.
The heart of the patent is an N-of-M authorisation scheme executed on the card itself. The card stores M authorised public keys. A transaction is signed only when the card receives at least N copies of that transaction, each signed by a different one of the M authorised keys, and has verified all of them inside the secure element (claims 1 and 12). A single stolen phone, laptop or key can therefore never move the assets — the quorum must be met on the card.
Every operation follows the same security model: the signing request reaches the card via NFC, the secure element verifies the quorum and signs internally, and only the signed transaction leaves the card for blockchain submission. The private key never leaves the secure element — genuine cold storage, with every security-critical step performed inside certified tamper-resistant hardware.
Built for NFTs: Secure Backup Cards and Prior-Use Detection
The granted claims further cover PIN-style identification as part of the authorisation (claim 4), key derivation from an on-card seed (claim 3), and an on-card signing log or counter that lets the owner detect whether a card has ever been used before — a tamper-evidence feature for cards delivered or stored as cold storage (claims 5 to 7). They also protect the secure creation of a backup card by transferring the key or seed and the authorisation protocol to a second secure element over an encrypted Elliptic-Curve Diffie-Hellman channel (claims 9 to 11 and 13).
Filed on 17 March 2021, at the height of the first NFT wave, the patent was conceived for high-value, non-fungible digital assets, where a single signature is irreversible: the multi-signature quorum, the backup card and the prior-use detection together give NFT holders, galleries and institutions hardware-enforced control that purely software-based wallets cannot offer.
FAQ: NFT Hardware Wallet Security
How do I store NFTs on a hardware wallet?
Cryptnox’s NFC crypto card wallet stores the private key for your NFT blockchain address inside a secure element chip Your NFTs remain on the blockchain, but the key that controls them is protected by tamper-resistant hardware All transactions — minting, transferring, or listing — are signed inside the secure element via a simple card tap
What is NFT cold storage?
NFT cold storage means keeping the private key that controls your NFT assets in hardware that is not connected to the internet Cryptnox’s smart card wallet achieves this naturally: the card has no battery, no Bluetooth, no WiFi — it only activates when physically tapped to an NFC-enabled device, making it a true cold storage solution for non-fungible tokens
Can you store NFTs offline?
Yes With Cryptnox, the private key controlling your NFTs is stored entirely offline inside the card’s secure element chip The NFTs themselves live on the blockchain, but the cryptographic key required to manage them never touches the internet, a computer hard drive, or any software environment
