CIS 3210 Lecture Notes - Lecture 39: Data Encryption Standard, Brute-Force Attack, Chosen-Plaintext Attack

• School: University of Guelph
• Department: Computing and Information Science
• Course: CIS 3210
• Professor: Xiaodong Lin

Document Summary

Cipher-text only attack: trudy has cipher text she can analyze. Known-plaintext attack: trudy has plaintext corresponding to cipher text (ex: in mono alphabetic cipher, trudy determines pairings for a,l,i,c,e,b,o,) Chosen-plaintext attack: trudy can get cipher text for chosen plaintext. Symmetric key cryptography - bob and alice share same (symmetric) key: k. The key is knowing substitution pattern in mono alphabetic substitution cipher. Symmetric-key nist standard, replaced des in 2001. Further, to limit the impact of a potential discovery by a cryptographic adversary, the shared secret key between alice and bob should be changed regularly and kept secure during distribution and in service. Would need to change the shared key very often, and on a very large network (of size n nodes) you would need n(n-1) / 2 keys. Requires sender and receiver know the shared secret key. Q: how to agree on key in the rst place (particularly if never met) Sender, receiver do not share secret key.