“The project developed two different prototypes based on the eCash design, which builds on the existing two-tier banking system. One design, eCash 1.0 (EC1), resembles a cash-like digital payment instrument. The second design, eCash 2.0 (EC2), investigates enhanced security features allowing for strong protection against and detection of counterfeiting.”

https://www.bis.org/about/bisih/topics/cbdc/tourbillon.htm