EXT0011: EdDSA Authentication

• Extension dependencies: none
• Document status: Discussion

Two-way authentication using EdDSA (Ed25519). Public key length: 32 bytes, signature: 64 bytes.

Both public keys known to both parties. Private keys never transferred. Device public key serves as unique identifier.

Authentication Process

1. Server sends 001A with its public key and random DCHALLENGE
2. Device verifies server key, responds with its public key and SCHALLENGE
3. Server sends 001B with signature of SCHALLENGE
4. Device responds with signature of DCHALLENGE

Unauthenticated clients have minimum rights (0000, 001A, 001B, Keep Alive).

Commands

001A Start Authentication

Request:

<TID> 3900 0042 001A <SPUBKEY> <DCHALLENGE>

Response:

<TID> 3900 0042 001A <DPUBKEY> <SCHALLENGE>

Field	Length	Description
SPUBKEY	32 bytes	Server public key
DPUBKEY	32 bytes	Device public key
SCHALLENGE	32 bytes	Random bytes for server to sign
DCHALLENGE	32 bytes	Random bytes for device to sign

Errors: 000A Server key mismatch, 000B Too many requests

001B Confirm Authentication

Request:

<TID> 3900 0042 001B <SSIGN>

Response:

<TID> 3900 0042 001B <DSIGN>

Field	Length	Description
SSIGN	64 bytes	Server signature of SCHALLENGE
DSIGN	64 bytes	Device signature of DCHALLENGE

Errors: 000A Invalid signature, 000B Not initialized/timeout, 000C Device busy

001C Create New EdDSA Secret

Change server public key and regenerate device key pair. Requires prior authentication.

Request/Response:

<TID> 3900 0022 001C <SPUBKEY>/<DPUBKEY>

Errors: 000A Key generation error