Seminar2_2010 - Seminar Seminar 2 Symmetric Encryption...

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eminar 2 Seminar 2 Symmetric Encryption & Message Confidentiality 1
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Outline • Conventional Encryption Principles • Conventional Encryption Algorithms ipher Block Modes of Operation • Cipher Block Modes of Operation • Location of Encryption Devices • Key Distribution 2
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Simple ways to protect Message Confidentiality Example 2.1 You choose a secret number, say the number 1, and add this to each of the digit in the string “123456”: 3456 123456 + 111111 234567 Figure 2.1 A Simple Algorithm Thus you will store the number “234567” instead. To recover the original number string, you just need to subtract the number “1” from each digit of e stored number. the stored number. Others: (i) Use of translation and reverse translation tables (transformations) (ii) Permutations 3
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Conventional Encryption Principles • An encryption scheme has five ingredients: – Plaintext – Encryption algorithm –Sec re t Key –C iphe r tex t – Decryption algorithm • Security depends on the secrecy of the key, not the secrecy of the algorithm 4
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Conventional Encryption Principles 5
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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) he way in which the plaintext is processed The way in which the plaintext is processed 6
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Different Types of Algorithms tream Cipher vs Block Cipher 1. Stream Cipher vs Block Cipher - algorithms that handle block of inputs together (block) -a lgorithms that handle each ‘entry’ separately (stream) 2. Public Key Algorithm vs Secret Key Algorithms - Secret key : the same key is being used for both encryption and decryption - Public key : use a pair of keys, one for encryption, and the other for decryption 7
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The different ways, or modes, of handling different blocks of data are ff r n way , r m , f an ng ff r n f a a ar known as the different Modes of Operations for block ciphers. When we carry out block encryption by processing each block of data separately, we say that we are using the Electronic Code Book (ECB) py ,y g E ( E ) mode. 1234 5678 Ciphertext C1 Ciphertext C2 Example : Encryption with ECB Mode Two types : Cipher Block Chaining (CBC) and ipher Feedback Model (CFB) Cipher Feedback Model (CFB) 8
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ipher Block Modes of Cipher Block Modes of peration Operation • Cipher Block Chaining Mode (CBC) – The input to the encryption algorithm is the XOR of the current plaintext block and the receding ciphertext block preceding ciphertext block. – Repeating pattern of 64-bits are not exposed i 1 i k i ] P [C E C = i 1 i i K i 1 i K K i K ) P (C ] [C D )] P (C [E D ] [C D = = 9 i i 1 i 1 i i K 1 i P P C C ] [C D C = =
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ipher Feedback Mode Cipher Feedback Mode onvert block cipher into a tream cipher Convert block cipher into a stream cipher Eliminates need to pad a message • Operates in real time • Each character can be encrypted and transmitted immediately receding iphertext
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This note was uploaded on 09/06/2010 for the course IT ICt211 taught by Professor Tan during the Spring '10 term at Singapore Institute of Management.

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Seminar2_2010 - Seminar Seminar 2 Symmetric Encryption...

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