KVAC unification

WabiSabi: Centrally Coordinated CoinJoins with Variable Amounts paper is based on the work The Signal Private Group System and Anonymous Credentials Supporting Efficient Verifiable Encryption which describes a cryptographic primitive called keyed-verification anonymous credential (KVAC) designed to be used by the Signal Messaging system. The researcher presented a credentials scheme which supports multiple attributes, this is, a credential can “contain” multiple pieces of information (eg. age, sex, eye color, department, dob, nationality or any other).

Wasabi uses exactly the same scheme except for the fact that Wasabi’s credentials only allow one attribute. It is for these reason that the concept of credential type was introduced, because instead of having one credential with two attributes: Amount and Vsize, there are two kind of credentials: Amount credential and Vsize credential.