Crypt Analysis

CryptAnalysis Lecture - Trying to find cipher text nature of - Knowing the algorithm used and finding out cipher text from plain and what the Key is likely to be Brute Force attack - He has the cigher text and he use's diff erent Keys for the plaintext getting the plaintext original message. Notes This type of attacks rely on the Crypt Analysis the knowledge of some gener al kha nature of the a Igorithm palus Perhap shis of the plain text or even 5 sample plain text cipher text pai Brute Force Attack. The attacker tries every possible on a piece of cipher text until intelligible translation to plain text i obtained After the Cipher text only attack attacker has : 1) Encoyption algorithm 2) Cipher text

and after known plaintext attack, the attacker has of crypt analyst has : 1) Encryption Algorithm 2) cipher Text 3) plain text - - aphertext Pairs with Key. - Unconditionally Secure and Computationally secure Algorithm - If a Cipher text is known by crypt analyst, he cannot find the key and Plain text and it is called unconditionally secure Scheme - An encyclin scheme is unconditionally Secure, if the cipher text generated in formation to determine uniquely by The scheme doesnot contain enough the corresponding plain text No matter how much cipies text is available Eg: One - time Pad JAY An encryption scheme is said to be two Computationally conditions secure are met if either : of the 1. The cost of breaking the cipher exceeds the value of the encrypted information 2) The time required to break the cipher exceeds the useful lifetime of the information