Nobody has access to the private keys, they are created by the chips inside Tangem Notes. You can't import or export these keys. You can't get them out in a lab, because the chip is an EAL6+ secure element. You can't hack the firmware — it's based on EAL6+ cryptographic libraries, has minimal attack surface and 100% audited both internally and by one of the best independent security groups.

Of course there's a limit to security and reverse–engineering labs in China get upgraded — we have a dynamic roadmap to improve security in anticipation of more sophisticated attacks and attack vectors.

Co-founder of Tangem here. The crypto value is on the Tangem Notes, inside the secure chip — in the form of a unique private key which is impossible to copy. You can redeem any Tangem Note directly to blockchain without a third party — using an open NFC protocol. We provided reference apps for Android and iOS (only Android can redeem / extract the value at the moment).

Tangem as a company does not hold any cryptocurrency associated with Tangem Notes — we're just developing the technology and making sure the banknotes are impossible to hack or tamper with at any point in the supply chain or in public circulation.

The redeemable nature of Tangem Notes mean you have to verify their current value over NFC when receiving them from someone you don't trust. We rely on the high and growing NFC smartphone penetration. Offline balance check will be available through trusted attestation, but for now an internet connection is required, because the app will check against the blockchain, using electrum nodes.