Đang chuẩn bị liên kết để tải về tài liệu:
Chapter 18: Network Security

Strong encryption algorithm Even if known, should not be able to decrypt or work out key Even if a number of cipher texts are available together with plain texts of them Sender and receiver must obtain secret key securely Once key is known, all communication using this key is readable | William Stallings Data and Computer Communications Chapter 18 Network Security Security Requirements Confidentiality Integrity Availability * Passive Attacks Eavesdropping on transmissions To obtain information Release of message contents Outsider learns content of transmission Traffic analysis By monitoring frequency and length of messages, even encrypted, nature of communication may be guessed Difficult to detect Can be prevented * Active Attacks Masquerade Pretending to be a different entity Replay Modification of messages Denial of service Easy to detect Detection may lead to deterrent Hard to prevent * Security Threats * Conventional Encryption * Ingredients Plain text Encryption algorithm Secret key Cipher text Decryption algorithm * Requirements for Security Strong encryption algorithm Even if known, should not be able to decrypt or work out key Even if a number of cipher texts are available together with plain texts of them Sender and receiver must obtain secret key securely . | William Stallings Data and Computer Communications Chapter 18 Network Security Security Requirements Confidentiality Integrity Availability * Passive Attacks Eavesdropping on transmissions To obtain information Release of message contents Outsider learns content of transmission Traffic analysis By monitoring frequency and length of messages, even encrypted, nature of communication may be guessed Difficult to detect Can be prevented * Active Attacks Masquerade Pretending to be a different entity Replay Modification of messages Denial of service Easy to detect Detection may lead to deterrent Hard to prevent * Security Threats * Conventional Encryption * Ingredients Plain text Encryption algorithm Secret key Cipher text Decryption algorithm * Requirements for Security Strong encryption algorithm Even if known, should not be able to decrypt or work out key Even if a number of cipher texts are available together with plain texts of them Sender and receiver must obtain secret key securely Once key is known, all communication using this key is readable * Attacking Encryption Crypt analysis Relay on nature of algorithm plus some knowledge of general characteristics of plain text Attempt to deduce plain text or key Brute force Try every possible key until plain text is achieved * Algorithms Block cipher Process plain text in fixed block sizes producing block of cipher text of equal size Data encryption standard (DES) Triple DES (TDES) * Data Encryption Standard US standard 64 bit plain text blocks 56 bit key * DES Encryption Algorithm * DES Single Iteration * Strength of DES Declared insecure in 1998 Electronic Frontier Foundation DES Cracker machine DES now worthless Alternatives include TDEA * Triple DEA ANSI X9.17 (1985) Incorporated in DEA standard 1999 Uses 3 keys and 3 executions of DEA algorithm Effective key length 168 bit * Location of Encryption Devices * Link Encryption Each communication link equipped at both ends All traffic secure High level of security .