Zero-knowledge: abstract of a tutorial

Zero-knowledge proofs are fascinating and extremely useful constructs. Their fascinating nature is due to their seemingly contradictory definition; zero-knowledge proofs are both convincing and yet yield nothing beyond the validity of the assertion being proven. Their applicability in the domain of cryptography is vast; they are typically used to force malicious parties to behave according to a predetermined protocol. In addition to their direct applicability in cryptography, zero-knowledge proofs serve as a good benchmark for the study of various problems regarding cryptographic protocols (e.g., "secure composition of protocols" and the "use of of the adversary\´s program within the proof of security"). We present the basic definitions and results regarding zero-knowledge as well as some recent developments regarding this notion.