Outline 曹天杰 Tianie 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 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
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 K Ee and a corresponding decryption rule dk∈D. Each eK:P→ C and dk:C→>Pare functions such that dek 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 Securit Primitives ymmetrIc-key Primitives Signatures Pseudorandom sequences Identification primitives Public-key ciphers Public-key Primitives Signatur 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 X E X, but it is computationally infeasible to find anyE X such that f(x) 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