第二章 Symmetric Encryption 电子商务信息安全与管理教学课件.pptVIP

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第二章 Symmetric Encryption 电子商务信息安全与管理教学课件.ppt

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第二章 Symmetric Encryption 电子商务信息安全与管理教学课件

Other Symmetric Block Ciphers Advanced Encryption Standard NIST（国家标准技术协会） call for proposals in 1997 Nov, 2001 – Rijndael Symmetric block cipher (128 bits) and key lengths 128, 192, 256 Other Symmetric Block Ciphers 4Transformations: Substitute Bytes Shift Rows Mix Columns Add Round Keyflash演示 Other Symmetric Block Ciphers International Data Encryption Algorithm (IDEA) 128-bit key Used in PGP Blowfish Easy to implement High execution speed Run in less than 5K of memory Cipher Block Modes of Operation Electronic Codebook Book 电码本模式(ECB) message is broken into independent blocks which are encrypted将信息划分成独立的分组进行加密 each block is encoded independently of the other blocks每一分组单独进行加密 Ci = DESK1 (Pi) uses: secure transmission of single values Cipher Block Modes of Operation(ECB) Cipher Block Modes of Operation Cipher Block Chaining Mode (CBC) The input to the encryption algorithm is the XOR of the current plaintext block and the preceding ciphertext block. Repeating pattern of 64-bits are not exposed Question With the ECB mode, if there is an error in a block of the transmitted ciphertext, only the corresponding plaintext block is effected. However, in the CBC mode, this error propagates. For example, an error in the transmitted C1 obviously corrupts P1 and P2.a. Are any blocks beyond P2 affected?b. Suppose that there is a bit error in the source version of P1. Through how many ciphertext blocks is this error propagated? What is the effect at the receiver? Cipher Block Modes of Operation CFB Cipher FeedBack密码反馈模式 (CFB) message is treated as a stream of bits result is feed back for next stage standard allows any number of bit (1,8 or 64 or whatever) to be feed back denoted CFB-1, CFB-8, CFB-64 etc Cipher FeedBack (CFB) Cipher FeedBack (CFB) Location of Encryption Device Link encryption: A lot of encryption devices High level of security Decrypt each packet at every switch End-to-end encryption The source encrypt and the receiver decrypts Payload encrypted