Anonymous delegation with non-frameable accountability

Construct a purpose-limited payment token that simultaneously provides payer anonymity, purpose attenuation through delegation, per-coin accountability, and non-frameability for delegated coins.

Background

The main token supports delegation and non-frameability but is not anonymous because the bank observes the per-coin values at issuance. The anonymous variant hides those values and provides payer unlinkability, but it drops delegation and replaces per-coin tracing with per-account tracing.

The paper therefore identifies the simultaneous achievement of anonymity, delegation, and non-frameable per-coin accountability as an unresolved construction problem.