On Fri 20 Apr 2018, SoylentNews published four criteria for analog currency and four criteria for digital currency [soylentnews.org].
On Mon 18 May 2018, Bank of England Staff Working Paper Number 725 [bankofengland.co.uk] by Michael Kumhof [former Stanford University economics professor] and Clare Noone [former Reserve Bank of Australia staffer] published four criteria for a Central Bank Digital Currency [CBDC]:
The core principles are: (i) CBDC pays an adjustable interest rate. (ii) CBDC and reserves are distinct, and not convertible into each other. (iii) No guaranteed, on-demand convertibility of bank deposits into CBDC at commercial banks (and therefore by implication at the central bank). (iv) The central bank issues CBDC only against eligible securities (principally government securities).
I'm not sure these count as four distinct criteria or that they are strong enough to be useful.