More on restrictive blind issuing of secret-key certificates in parallel mode

A minimal variation is proposed of a recently described secret-key certificate scheme that is derived from the Schnorr signature scheme.The issuing protocol of the variation is conjectured to be restrictive blind in parallel mode, motivated by a recent argument of Schoenmakers.The variation demonstrates that the double use of a generator is not problematic in any way, contrary to the belief expressed by Schoenmakers. A more profound argument for the conjectured security in parallel mode is provided, and similar variations are described for secret-key certificates based on Brickell-McCurley signatures. To create some order in the variety of restrictive blind certificate schemes that have been proposed to date, their specific merits and limitations are categorized and discussed.