#Block cipher how to

Shannons Theory of Secrecy Systems (cont.)Showed that the one-time pad is the only unconditionally secure cipher, provided the key is truly random and used once only Showed that a Book cipher is not secureI.e. Shannons Theory of Secrecy SystemsClaude Shannon wrote some of the pivotal papers on modern cryptology theory C E Shannon, 'Communication Theory of Secrecy Systems', Bell System Technical Journal, Vol 28, Oct 1949, pp 656-715 C E Shannon, 'Prediction and Entropy of printed English', Bell System Technical Journal, Vol 30, Jan 1951, pp 50-64 In these he developed the concepts of:Entropy of a messageRedundancy in a languageTheories about how much information is needed to break a cipher Defined the concepts of computationally secure vs unconditionally secure ciphers

#Block cipher how to

Modern Block CiphersOne of the most widely used types of cryptographic algorithms For encrypting data to ensure secrecyAs a cryptographic checksum to ensure integrityFor authentication servicesUsed because they are comparatively fast, and we know how to design themWell look in particular at DES (Data Encryption Standard)īlock vs Stream CiphersBlock ciphers process messages in into blocks, each of which is then en/decrypted So all bits of block must be available before processingLike a substitution on very big characters64-bits or more Stream ciphers process messages a bit or byte at a time when en/decrypting Recall: Private-Key Encryption AlgorithmsAlso called single-key or symmetric key algorithmsBoth parties share the key needed to encrypt and decrypt messages, hence both parties are equalClassical ciphers are private-keyModern ciphers (developed from product ciphers) include DES, Blowfish, IDEA, LOKI, RC5, Rijndael (AES) and others Lawrie Brown at the Australian Defense Force Academy whose PowerPoint slides provided the basis for these slides. Modern Block Ciphers and the Data Encryption Standard (DES)Īgain Special Thanks to Dr.