Security Attacks, Mechanisms, and Services

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.

Passive Attacks These are in the nature of eavesdropping on, or monitoring of, transmission Attempts to learn or make use of information from system Does not affect system resources Difficult to detect because they do not involve any alteration of data Traffic normally sent and received in a normal fashion Attempt is made to prevent the success of these attacks, usually by means of encryption Thus emphasis is on prevention rather than detection

Passive Attacks(cont….) Release of message contents is easily understood Telephonic conversation, e-mail message, or a transferred file may contain sensitive information Emphasis is to prevent opponent from learning

Passive Attacks(cont….) Traffic Analysis Observe patterns of messages Could determine identity and location of communicating hosts Could observe the frequency and length of messages being exchanged

Active Attacks Involves modification of data, or false creation of data Attempt to alter system resources or affect their operations Difficult to prevent active attacks Emphasis is to detect active attacks and recover from the damage

Active Attacks(cont….) Masquarade One entity pretendes to be a different entity E.g. Authentication sequences can be captured Replay Involves passive capture of data unit and its subsequent retransmission to produce unauthorized effect

Active Attacks(cont….) Modification of Message Means some portion of a legitimate message is altered, or messages are reordered or delayed, to produce unauthorized affect E.g. ” Allow John Smith to read confidential file accounts” is modified to ” Allow Fred Brown to read confidential file accounts”

Active Attacks(cont….) Denial of Service Prevents normal use of communication facilities Disabling or overloading of entire network

Conventional Encryption Principles An encryption scheme has five ingredients: Plaintext Encryption algorithm Secret Key Ciphertext Decryption algorithm Security depends on the secrecy of the key, not the secrecy of the algorithm

Conventional Encryption Principles

Cryptography Classified along three independent dimensions: The type of operations used for transforming plaintext to ciphertext The number of keys used symmetric (single key) asymmetric (two-keys, or public-key encryption) The way in which the plaintext is processed

Cryptography can be characterized by: type of encryption operations used substitution / transposition / product number of keys used single-key or private / two-key or public way in which plaintext is processed block / stream

Average time required for exhaustive key search Key Size (bits) Number of Alternative Keys Time required at 106 Decryption/µs 32 232 = 4.3 x 109 2.15 milliseconds 56 256 = 7.2 x 1016 10 hours 128 2128 = 3.4 x 1038 5.4 x 1018 years 168 2168 = 3.7 x 1050 5.9 x 1030 years