Outline 曹天杰 Tianjie Cao ticao@cumt.edu.cn College of Computer Science and echnology china University of Mining and Technology Xuzhou, China 中国矿业大学计算机科学与技术学院 2003.6.16
曹天杰 Tianjie Cao tjcao@cumt.edu.cn College of Computer Science and Technology, China University of Mining and Technology, Xuzhou, China 中国矿业大学计算机科学与技术学院 2003.6.16 Outline
Attacks. Services, and mechanisms Security attack: Any action that compromises the securi of information Security Mechanism: A mechanism that is designed to detect, prevent, or recover from a security attack Security service: a service that enhances the security of data processing systems and information transfers. A security service makes use of one or more security mechanisms
Attacks, Services, and Mechanisms * Security Attack: Any action that compromises the security of information. * Security Mechanism: A mechanism that is designed to detect, prevent, or recover from a security attack. * Security Service: A service that enhances the security of data processing systems and information transfers. A security service makes use of one or more security mechanisms
Cryptosystem A cryptosystem is a five -tuple(P, C, K, E,D), where the following conditions are satisfied 1. P is a finite set of possible plain teXts 2. C is a finite set of possible ciphertexts 3. K, the keyspace, is a finite set of possible keys 4. For each kEK, there is an encryption rule eK E E and a corresponding decryption rule dk∈D. Each ek:P> C and d,:C→Pare functions such that dex( x )=x for every plaintext X∈P
Cryptosystem • A cryptosystem is a five -tuple (P, C, K, E, D), where the following conditions are satisfied: • 1. P is a finite set of possible plain texts • 2. C is a finite set of possible ciphertexts • 3. K, the keyspace, is a finite set of possible keys • 4. For each kK, there is an encryption rule eK E. and a corresponding decryption rule dK D). Each eK : P → C and dK : C → P are functions such that dK(eK(x)) = x for every plaintext x P
Taxonomy of cryptographic primitives Arbitrary length hash functions Unkeyed Primitives One-way permutations Random sequences Block ciphers Symmetric-key ciphers Stream Arbitrary length hash functions(MACs) ciphers Security Symmetric-keyl Primitives Primitives Signatures Pseudorandom sequences Identification primitives Public-key ciphers Public-key Primitives Signatures Identification primitives
Taxonomy of cryptographic primitives. Arbitrary length hash functions One-way permutations Random sequences Symmetric-key ciphers Arbitrary length hash functions(MACs) Signatures Pseudorandom sequences Identification primitives Public-key ciphers Signatures Identification primitives Unkeyed Primitives Symmetric-key Primitives Public-key Primitives Security Primitives Block ciphers Stream ciphers
Background on Functions(ctd) one-way function if f(x)is easy to compute for all XE X, but it is computationally infeasible to find any XE X such that f(x)=y trapdoor one-way function if given trapdoor information, it becomes feasible to find an x E X such that f(x)y
Background on Functions (ctd) • one-way function if – f(x) is easy to compute for all x X, but – it is computationally infeasible to find any x X such that f(x) =y. • trapdoor one-way function if – given trapdoor information, it becomes feasible to find an x X such that f(x) =y