Single-Purpose Shared Key Establishment
Single-Purpose Shared Key Establishment (SPSKE) is a mechanism for establishing a shared-secret keychain item on two or more devices in-band without an administrator ever learning the shared secret. This enables the establishment of long-lived automation relationships. This shared key can then be associated with a very limited single-purpose identity to allow devices to perform actions on each other without granting the ability to perform unauthorized actions. The intent is to enable a "capability-like" security model.
There are two variants: one for establishing a shared key between two devices, and one for establishing a shared key between a group of devices. The exact mechanism is TBD, but it would generally work like this:
- The administrator calculates a temporary shared secret, P.
- A "prepare-SPSKE" command is sent to Device A with the desired key
identifier and the value of P.
- Upon success, a location LOC is returned, which (if relative) is expanded to a fully specified URI. When the process is finished, this will be the address of the newly created keychain item for Device A. Next step must be completed within five minutes or LOC will become invalid.
- A "calc-SPSKE" command is sent to Device B with the desired key
identifier, the value of P, and the value of LOC.
- Upon success, a location to the newly created keychain item for Device B is returned. LOC can then be considered the location of the newly created keychain item for Device A.
- The administrator can then configure the newly created keychain items as appropriate, without ever learning the shared secret they contain.