A Formulation for Ideal Signature Functionality and Its Realization

Universal composition framework, UC, provides a methodology for designing and analyzing protocols. A secure protocol/task can be formulated to an ideal functionality, translate some realistic schemes into an ideal protocol so that it can securely emulate the ideal functionality. UC theory ensures the security of protocols is maintained under a general protocol composition operation. Signature is a primary cryptographic task. The present formulation of ideal signature functionality is introduced and some flaws are pointed out, and then an improved signature functionality is presented and proven that it is securely realized by precisely those signature scheme that is equivalent to existential unforgery against chosen- message attacks, EU-CMA.