CS283 Lecture 2 - Part 2 - Block Ciphers - 20090915

# CS283 Lecture 2 - Part 2 - Block Ciphers - 20090915 -...

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Unformatted text preview: Lecture 2 – Part 2 - Block Ciphers: DES, GWU SPNs, AES CS 172/283 Autumn 2009 ome of this slide set is from: M eys Tutorial on Linear and Differential Some of this slide set is from: H. M. Heys, "A Tutorial on Linear and Differential Cryptanalysis", Technical Report CORR 2001-17, Centre for Applied Cryptographic Research, Department of Combinatorics and Optimization, University of Waterloo, Mar. 001 (Also appears in ryptologia vol XXVI no 3 pp 189 21 2002 ) 2001. (Also appears in Cryptologia, vol. XXVI, no. 3, pp. 189-221, 2002.) lock Cipher efinition Block Cipher – Definition (From Bishop New 10,2) Let E be an encipherment algorithm, and let E k (b) be the encipherment of message b with key k. Let a message m = b 1 b 2 …. , where each b i is of a fixed length. Then a block cipher is a cipher for which E k (m) = E (b )E (b )…… k ( 1 ) k ( 2 ) GWU CS 172/283 - Autumn 2009 Holmblad - Lecture 02 – Part 2 - Rev 20090915 2 Block Cipher lectronic Code book) (electronic Code book) Plain Text in fixed length blocks Cryptovariable 1 1 … 1 lack Box 1 … 1 . 1 1 … 1 Black Box 1 1 … 1 1 iphertext in fixed length blocks GWU CS 172/283 - Autumn 2009 Holmblad - Lecture 02 – Part 2 - Rev 20090915 3 Ciphertext in fixed length blocks lock Ciphers Implement a Block Ciphers Implement a Permutation Plain Text (PT) Cipher Text (CT) 0 0 0 0 1 0 0 0 0 0 0 1 0 0 1 0 0 0 1 0 1 0 0 1 0 0 1 1 0 0 0 0 0 1 0 0 1 0 1 0 0 1 0 1 0 1 0 0 0 1 1 0 1 0 1 1 This PT Always encrypts to this CT 0 1 1 1 0 0 1 1 1 0 0 0 1 1 0 0 1 0 0 1 0 1 0 1 1 0 1 0 1 1 0 1 OTE: The 1 0 1 1 1 1 1 1 1 1 0 0 0 1 1 0 1 1 0 1 1 1 1 0 1 1 1 0 0 1 1 1 1 1 1 1 0 0 0 1 NOTE: The permutation is on the four-bit words, not on e bits in the words GWU CS 172/283 - Autumn 2009 Holmblad - Lecture 02 – Part 2 - Rev 20090915 4 the bits in the words. lock Decryption Implements the Block Decryption Implements the Reverse Permutation Plain Text (PT) Cipher Text (CT) 0 0 0 0 1 0 0 0 0 0 0 1 0 0 1 0 0 0 1 0 1 0 0 1 0 0 1 1 0 0 0 0 0 1 0 0 1 0 1 0 0 1 0 1 0 1 0 0 0 1 1 0 1 0 1 1 Always decrypts to this PT This CT 0 1 1 1 0 0 1 1 1 0 0 0 1 1 0 0 1 0 0 1 0 1 0 1 1 0 1 0 1 1 0 1 1 0 1 1 1 1 1 1 1 1 0 0 0 1 1 0 1 1 0 1 1 1 1 0 1 1 1 0 0 1 1 1 1 1 1 1 0 0 0 1 GWU CS 172/283 - Autumn 2009 Holmblad - Lecture 02 – Part 2 - Rev 20090915 5 ata Encryption Standard Data Encryption Standard •Designed as a US Federal Standard for encryption of sensitive but non-classified information • it riented Bit oriented •Developed by a team at IBM during the period 1973–1974 and based on an earlier algorithm, Horst Feistel's Lucifer cipher. •Symmetric Key (i.e. encyption and decryption use same key) •Uses both bit transposition and bit substitution and is ometimes referred to as a roduct ipher sometimes referred to as a product cipher GWU CS 172/283 - Autumn 2009 Holmblad - Lecture 02 – Part 2 - Rev 20090915 6 ata Encryption Standard (cont’d) Data Encryption Standard (cont d) •Input, output, and (input) key are each 64 bits long...
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CS283 Lecture 2 - Part 2 - Block Ciphers - 20090915 -...

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