Criptography
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This document provides an overview of cryptography. It discusses traditional cryptography techniques like the Caesar cipher and shift ciphers. It also explains symmetric and asymmetric key cryptography, giving examples like DES, RSA, and their uses. Cryptographic services like authentication, data integrity, non-repudiation, and confidentiality are mentioned. The document notes how cryptography is widely used today in network security, banking transactions, and military communications.
Criptography
- 1. Department of Computer Application Kalinga Institute of Industrial Technology, Bhubneshwar By: Amrita Mohapatra Reg. No.: 0305203034 E-mail : amrita_19832003@yahoo.co.in
- 2. How the concept of cryptography arises Technical Meaning
- 3. Plain text Cipher text Encryption Algorithm Decryption Algorithm
- 4. Mathematically C = E (M ,K ) M = D (M , K )
- 5. Traditional methods of cryptography Substitution Technique Caesar Cipher Plain Text M consists of the letter A, B… Z. When computing a cipher text “add 3” modulo 26 to each letter. i.e. A->D, B->E… X->A, Y->B, Z->C. Do it for every letter. e.g. CAESAR -> FDHVDU. The security remains if you hide the fact that you are applying Caesar cipher to your message.
- 6. Shift Ciphers Caesar Cipher Shift Cipher Pick a secret key K from 0-25. Add K modulo 26 to all letters. C = M+K modulo 26 For Example :- M = HAL and K = 1 we increment each character of HAL by one and find C = IBM
- 7. Cryptanalysis of shift Ciphers Pivot
- 8. Substitution CCiipphheerr ((TTaakkiinngg ppeerrmmuuttaattiioonn ooff lleetttteerrss )) SSeeccrreett MMeessssaaggee :: -- TTKK IILL KKQQ JJKKTT TTKK IILL TTBBSSTT CCRR TTBBLL OOUULLRRTTCCKKJJ OOrriiggiinnaall MMeessssaaggee ::-- TTOO BBEE OORR NNOOTT TTOO BBEE TTHHAATT IISS TTHHEE QQUUEESSTTIIOONN
- 9. TRANSPOSITION TECHNIQUE Transposition ciphers are rarely encountered nowadays. They differ from both code systems and substitution ciphers; in a transposition cipher the letters of the plaintext are shifted about to form the cryptogram.
- 10. Types of cryptography • symmetric key cryptography •Asymmetric key cryptography
- 11. Symmetric Key Cryptography In this kind of encryption the key used for encryption and the key used for decryption are the same. It is also called as secret key cryptography. i.e. Alice and Bob share a key and use that both for encryption and decryption. We can think this as Alice and Bob together by a lock which has two keys of similar kind within it. Alice and Bob both can lock and unlock the message as they have the same key. Examples: DES, 3-DES, RC4, RC5 etc. (these are the cryptographic algorithms currently in use)
- 12. Asymmetric Key Cryptography In this kind of encryption technique the key used for encryption and the key used for decryption are different. This is also called as Public Key cryptography. Each user has two keys – one public key, which is revealed to all users, and one private key, which remains a secret. The private key and the public key are mathematically linked. Encryption is performed with the public key and decryption is performed with the private key. It is something like Alice wants to receive a message from Bob, and then she will give her private key to Bob. Bob can lock the message with the private key and send to Alice. No one other than Alice can unlock the message as unlocking needs private key and only Alice will be knowing her private key. (Let us forget about the detail for now as they are big mathematical calculations).
- 13. Cryptographic services • User Authentication
- 14. Data authentication • Data integrity Data origin authentication
- 15. Non-repudiation of origin Data confidentiality
- 16. Cryptography Today DES algorithm (a symmetric key) is a famous algorithm and widely used. But it was proved that it can be broken in just 24 hours with the help of a super computer and a huge number of computers working in parallel. That is why public key cryptography came into picture and RSA algorithm was designed which is widely used now-a-days. Cryptography is mostly used in network security and secret military communications. With the help of digital signature, digital certificate (not discussed due to limitation of the scope) the authenticity and truth of a particular digital piece is well defined. Hash functions and Message Authentication Codes are there to make sure that what message goes is not modified. In case of money transaction in Banks through network cryptography is a must, otherwise their would be a havoc in the economy.