Frian of Cryptography means secret and graphy means of writing crypto, 80 cryptography is the art Secret writing. plain text i It is the intelligable form of - (PT) text or original message. - Cipher Text - text. coded form of an original (CT) 274 - Encryption Encyphering it is the process of converting plain text into cipher text It is the process of converting cypher Decryption I Decyphening text into plain. text - Crypt Analysis / Breaking the code Trying to find the cypher text, and the person who does this is called - crypto logy crypt analyst. Cryptography and crypt Analysis Y togetherly Called cryptology. Symmetric Cypher Model ( shared secret Key K by the sender and key receiver) PT PT Encryption decryption Alacation Algorithm Algorithm (DES). Transmitted CT
- In this model, same they is usey at the Sender and receiving sides, i.e same key is used for encryption and decryption symmetrical encryption is also called conventional encryption or single Key encopy . DES - Data Eneryption Algorithm 2 methods used in Eneryption Substituitor Eg: ab c(PT)is substituted by def(CI), the key value used is 3 2) Permutation Eg: abc(PT) rearranged as bac(TT) - Here rearranging in any order is done: Key key is a value which is independent of that of plain text / Depending upon key value, cypher text changes. / Output changes as per the keys used. Security Aspects of a message / Eneryption algorithm should be strong enough Sender and the receiver should get the key in a secure fashion
X crypt ^ Analyst K x E y M D Destin Algorithra Algorithm ahin K secure channel Keysoure 1= Ek (x) where Y- - CT, E - -encryption, K-Key X-PT X= DK(Y) where D-decryption Q. How cytographic system differ from other systems 1) Type of operations used for transforming plain text to cypher text ii E i.e substitution and Permutation 2) No.of keys used. 3) The way in which, the plain text is processed i) Stream cypte eipher ii) Block cipher stream cipher Continuous processing of plain text is done Block cipher process ing of plain text is done as a block.
2 attacks to Cryptographic systems : 1) Crypt-Analysis 2) Brute Force attack.