# Secondary TDA

TDA is an acronym that stands for Trusted Digitial Assistant, a digital twin. Inherently it is a physical device that serves its holder primarily public key cryptography related operations and storage for raw cryptographic material. These two features are opaque to the holder and the holder sees it as a device that securely signs and keep confidential information. Furthermore `secondary` TDA is in a relationship with primary TDA, that controls the relation in the sense of controlling all the SCID's established on Secondary TDA. Therefore primary TDA is a custodian of any number of secondary TDA's.