Schnorr identification under concurrent attack ⇒ Schnorr identification protocol

Fully-black-box reduction · standard model · folklore · security loss: none

Statement

If the Schnorr identification protocol is secure against impersonation under concurrent attack, it is secure against impersonation under passive attack, with the same advantage — folklore.

Sketch

A concurrent attacker simulates the passive attacker’s transcript oracle by running prover sessions one at a time as the honest verifier, with uniform challenges, and then forwards the impersonation phase unchanged.