PPT-Cryptography Lecture 17 Feistel

networks Feistel networks Build invertible permutation from noninvertible components One round Keyed round function f 01 n x 01 l 2 01 l 2 F k1 L0 R0 L1 R1. However computational aspects of lattices were not investigated much until the early 1980s when they were successfully employed for breaking several proposed cryptosystems among many other applications It was not until the late 1990s that lattices w 897 Special Topics in Cryptography Instructors Ran Canetti and Ron Rivest Lecture 25 PairingBased Cryptography May 5 2004 Scribe Ben Adida 1 Introduction The 64257eld of PairingBased Cryptography has exploded Sixth Edition. by William Stallings . Chapter 3. Block Ciphers and the Data Encryption Standard. “But . what is the use of the cipher message without the cipher. ?”. -- The Valley of Fear, . Sir Arthur Conan Doyle. Chapter 3. Fifth Edition. by William Stallings . Lecture slides by . Lawrie. Brown. Content. Block Cipher Principles. The Data Encryption Standard. Simplified-DES. DES Details. DES Design Issues and Attacks. Sixth Edition. by William Stallings . Chapter 3. Block Ciphers and the Data Encryption Standard. “All the afternoon Mungo had been working on Stern's code, principally with the aid of the latest messages which he had copied down at the Nevin Square drop. Stern was very confident. He must be well aware London Central knew about that drop. It was obvious that they didn't care how often Mungo read their messages, so confident were they in the impenetrability of the code.”. Sixth Edition. by William Stallings . Chapter 3. Block Ciphers and the Data Encryption Standard. “All the afternoon Mungo had been working on Stern's code, principally with the aid of the latest messages which he had copied down at the Nevin Square drop. Stern was very confident. He must be well aware London Central knew about that drop. It was obvious that they didn't care how often Mungo read their messages, so confident were they in the impenetrability of the code.”. Lect. . 6. : . Block . Ciphers. 2. Model of Symmetric Cryptosystem. E. D. Shared Secret Key. Shared Secret Key. Key. K. Secure Channel. Insecure Channel. Plaintext. M. Ciphertext . C. Plaintext. M. 1. Administrative Note. Professor Blocki is traveling and will be back on Wednesday. . E-mail: . jblocki@purdue.edu. . Thanks to Professor Spafford for covering the first lecture!. 2. https://www.cs.purdue.edu/homes/jblocki/courses/555_Spring17/index.html. We have discussed two classes of cryptographic assumptions. Factoring-based (factoring, RSA assumptions). Dlog. -based (. dlog. , CDH, and DDH assumptions). In two classes of groups. A. ll these problems are believed to be “hard,” i.e., to have no polynomial-time algorithms. Consider first the case where there is no final key-mixing step. Possible to get the key immediately!. What about a full 1-round SPN? . Attack 1: for each possible . 1. st. -round. key, get corresponding 2. Cyclic group G of order q with generator g.  G.  . G = {g. 0. , g. 1. , …, g. q-1. }. For any h .  G, define . log. g. h .  {0, …, q-1} as. . log. g. h = x  . The . art and science of concealing the messages to introduce secrecy in . information security . is recognized as cryptography. .. The word ‘cryptography’ was coined by combining two Greek words, ‘Krypto’ . Crypto is amazing. Can do things that initially seem impossible. Crypto is important. It impacts each of us every day. Crypto is fun!. Deep theory. Attackers’ mindset. Necessary administrative stuff. Feistel. networks. Feistel. networks. Build (invertible) permutation from . non-invertible. components. One round:. Keyed round function f: {0,1}. n. x {0,1}. l. /2. . {0,1}. l. /2. F. k1. (L0, R0) .