Cryptographic assets

The Cryptnox Hardware Wallet card manages several cryptographic assets throughout its lifecycle. This section provides an overview of all key material, credentials, and derived secrets handled by the card.

Factory Dual Basic Group Secret

Scope	Secure Element (factory-loaded)
Description	EC secret used for the dual generation protocol and to sign public material exchanged between paired cards. Protects the integrity of the dual-gen exchange.
Notes	Loaded at factory; used in dual generation signatures.

Card long-term attestation key

Scope	Secure Element (card keypair)
Description	Card’s permanent EC keypair (R1) used to sign the card certificate and authenticate ephemeral session keys.
Notes	Readable only as the certificate via `GET MANUFACTURER CERTIFICATE` / `GET CARD CERTIFICATE`.

Session ephemeral private key

Scope	Secure Element (ephemeral, per session)
Description	Short-lived EC private key generated inside the card and used for ECDH in the secure channel. Never exported.
Notes	Exposed externally only as the card’s ephemeral public key inside the basic card certificate (`GET CARD CERTIFICATE`).

Pairing key

Scope	Card secure storage (32 bytes)
Description	The 32-byte secret used to derive AES/MAC session keys with a host for the authenticated secure channel. There is one pairing key slot; can be public if desired but normally kept secret.
Notes	Set at `INIT`; used in `OPEN SECURE CHANNEL` key derivation; changeable with `CHANGE PAIRING KEY`. Fallback: a PUK-derived pairing key (SHA-256³² of PUK) can be used (index `0xFF`).

Secure Channel session keys (AES / MAC)

Scope	Volatile (session only)
Description	Keys derived from ECDH(SessionCardPriv, SessionUserPub) \|\| PairingKey \|\| SessionSalt via SHA-512, split into AES and MAC keys. Protect confidentiality and integrity of APDUs while the channel is open.
Notes	Derived during `OPEN SECURE CHANNEL`. Not persistent.

PIN

Scope	Card secure storage
Description	User numeric PIN (4–9 digits) used to authenticate the user for most protected operations. PIN verification state is session-valid until a signature or deselect/power-off.
Notes	`INIT`, `VERIFY PIN`, `CHANGE PIN`, `UNBLOCK PIN`. Retry counters and power-cycle rules apply.

PUK

Scope	Card secure storage (12 bytes)
Description	Card reset/unblock secret. Used to unblock PIN, authorize PUK-protected changes (e.g., change pairing key, set pinless path, set pub export), and perform `RESET`.
Notes	`INIT`, `RESET`, `CHANGE PAIRING KEY`, `SET PIN AUTH`. Unlimited attempts but throttled with power-cycle behavior.

PUK-derived pairing fallback

Scope	Derived (fallback)
Description	Deterministic pairing key obtained by hashing the PUK 32 times with SHA-256; usable as pairing key index `0xFF` if pairing information is lost.
Notes	Used via `OPEN SECURE CHANNEL` with `P1=0xFF`.

User private keys (off-card)

Scope	Host device (e.g., TPM / Secure Enclave)
Description	Private keys kept on a host device used to perform challenge-response authentication against the card. The card stores only the corresponding public key. These act as PIN replacements.
Notes	Card stores public keys in slots via `ADD USER KEY`; verification via `CHECK USER KEY`. Private keys must be protected by the host.

FIDO credential (slot 3)

Scope	Card slot (credential ID + public key)
Description	FIDO credential identifier and associated EC public key. Used to verify WebAuthn-style signatures for PIN replacement or signing authorization.
Notes	`ADD USER KEY` (slot 3) stores credential ID length, credential ID, EC public key, and PUK. Verified via `CHECK USER KEY`.

Pinless path derivation settings

Scope	Card secure storage
Description	The BIP32 derivation path used for PIN-less signing (e.g., `m/43'/60'/1581'/...`); guarded by PUK to set/unset. Enables transactions without PIN when used via the pinless `SIGN` mode.
Notes	`SET PINLESS PATH` with PUK. Pinless signing via `SIGN` with `P1=0x03`.

Dual-generation partial secrets

Scope	Secure Element (temporary during dual-gen)
Description	During the dual-generation protocol, two cards each generate a partial secret and exchange signed public material to produce a shared seed (SHA-256(ECDH)). Each card stores its part; the final shared seed becomes the card seed.
Notes	`LOAD KEY` with `P1=0x04` / `P1=0x05` sequence. Signature checks use the Basic Group Secret.

Master seed

Scope	Secure Element (non-exportable)
Description	The 256-bit master seed (BIP32 / SLIP-0010) – the root of all derived blockchain keys. From this single seed, three independent key hierarchies are derived: secp256k1 (Bitcoin, Ethereum), secp256r1 (FIDO, secure messaging), and EdDSA (Ed25519, Solana, Cardano). This is the ultimate cryptographic asset: it cannot be read or exported, only destroyed via `RESET` with PUK.
Notes	Generated on-card (`GENERATE KEY`) or loaded (`LOAD KEY` with `P1=0x03`). Once set, it cannot be changed except by `RESET` with PUK.

Important

All cryptographic assets stored in the Secure Element are strictly non-exportable. Private keys and seeds never leave the card boundary. Recovery is only possible through dual-generated backup cards or re-importing an externally held seed.