Accumulator

The protocol is parameterized over an accumulator type which must support the following functionality:

• \(WRITE(cm)\) adds an element to the accumulator, returning the witness used to prove membership.
• \(WITNESS(cm)\) for a given element, returns the witness used to prove membership if the element is present, otherwise returns nothing.
• \(VERIFY(cm, w, acc)\) verifies the membership proof for an element \(cm\) with a membership witness \(w\) in the accumulator \(acc\).
• \(ACC()\) returns the accumulator.