Cryptography with caesar Cipher
- 1. 11/6/2017 Ciesar Cipher 111/6/2017 Ciesar Cipher 1 Topic Caesar Cipher Encryption Technique MSC (Cs)-I (1ST SEM) Year 2017-18 Submitted to Submitted by Dr. H.S. HOTA (HOD) Dushhyant Kumar (Department of CSA) Roll No. 06
- 2. 11/6/2017 Ciesar Cipher 2 Content
- 3. 11/6/2017 Ciesar Cipher 3 Introduction The word ‘cryptography’ was coined by combining two Greek words, ‘Krypto’ meaning hidden and ‘graphene’ meaning writing. Hieroglyph − The Oldest Cryptographic Technique The first known evidence of cryptography can be traced to the use of ‘hieroglyph’. Some 4000 years ago, the Egyptians used to communicate by messages written in hieroglyph. This code was the secret known only to the scribes who used to transmit messages on behalf of the kings. Why need Cryptography? Goal :- Secure communication(Protect data from Hackers & Crackers) 1. Confidentiality:- protection of data from unauthorized disclosure 2. Authentication:- The authentication service is concerned with assuring that a communication is authentic persion. 3. Integrity:- assurance that data received is as sent by an authorized entity
- 4. 11/6/2017 Ciesar Cipher 4 Introduction
- 5. 11/6/2017 Ciesar Cipher 5 Introduction Passive Attack: Traffic Analysis
- 6. 11/6/2017 Ciesar Cipher 6 Introduction Active Attack: Interruption Block delivery of message
- 7. 11/6/2017 Ciesar Cipher 7 Introduction Fabricate message Active Attack: Fabrication
- 8. 11/6/2017 Caesar Cipher 8 Introduction Modify messageModify message Active Attack: Modification
- 9. 11/6/2017 Ciesar Cipher 9 Introduction Human being from ages had two inherent needs − (a) to communicate and share information and (b) to communicate selectively. These two needs gave rise to the art of coding the messages in such a way that only the intended people could have access to the information. Unauthorized people could not extract any information, even if the scrambled messages fell in their hand.
- 10. 11/6/2017 Ciesar Cipher 10 What is cryptography? Cryptography:- The art or science encompassing the principles and methods of transforming an intelligible message into one that is unintelligible, and then retransforming that message back to its original form. Cryptography can characterize by: – type of encryption operations used • substitution / transposition – number of keys used • single-key or private / two-key or public – way in which plaintext is processed • block / stream
- 11. 11/6/2017 Ciesar Cipher 11 Basic Terminology
- 12. 11/6/2017 Ciesar Cipher 12 Symmetric Encryption
- 13. 11/6/2017 Ciesar Cipher 13 Symmetric Cipher Model
- 14. 11/6/2017 Ciesar Cipher 14 Requirements Two requirements for secure use of symmetric encryption: – a strong encryption algorithm. – a secret key known only to sender / receiver. Y = EK(X) X = DK(Y) ¨assume encryption algorithm is known ¨implies a secure channel to distribute key Cipher text (y) Plain text (x) Key (K) Encryption(E) Decryption(D)
- 15. 11/6/2017 Ciesar Cipher 15 Classical Encryption Technique 1. Substitution Ciphers:- where letters of plaintext are replaced by other letters or by numbers or symbols. OR if plaintext is viewed as a sequence of bits, then substitution involves replacing plaintext bit patterns with cipher text t bit patterns. Types of Substitution technique are :- A. Caesar Cipher B. Hill Cipher C. Polyalphabetic Ciphers D. One-Time Pad E. Playfair Cipher F. Monoalphabetic Ciphers 2. Transposition technique
- 16. 11/6/2017 Ciesar Cipher 16 Caesar Cipher Caesar Cipher earliest known substitution cipher “by Julius Caesar” first attested use in military affairs replaces each letter by 3rd letter. example: meet me after the toga party PHHW PH DIWHU WKH WRJD SDUWB Caesar Cipher ¨can define transformation as: a b c d e f g h i j k l m n o p q r s t u v w x y z D E F G H I J K L M N O P Q R S T U V W X Y Z A B C replaces each letter by 3rd letter
- 17. 11/6/2017 Ciesar Cipher 17 Caesar Cipher Caesar Cipher can define Mathematical transformation as: 1. Now we apply the same method to calculation for encryption using the Caesar cipher. 2. First we convert the letters of the alphabet to number so that we can operate on them mathematically. 3. We convert ‘a’ to 0, ‘b’ to 1, ‘c’ to 3.right through to ‘z’ 25 as shown below. then have Caesar cipher as: C = E(p) = (p + k) mod (26) p = D(C) = (C – k) mod (26)
- 18. 11/6/2017 Caesar Cipher 18 Caesar Cipher Caesar Cipher transformation Example: 1. Steps- Encryption and decryption process using Caesar cipher 2. Choose Plain text (original message). 3. Applying Caesar cipher replaces each letter by 3rd letter algorithm 4. Use key for Encryption Key= Number of shift alphabet called key Hello friend Plain text a b c d e f g h i j k l m n o p q r s t u v w x y z D E F G H I J K L M N O P Q R S T U V W X Y Z A B C
- 19. a b c d e f g h i j k l m n o p q r s t u v w x y z D E F G H I J K L M N O P Q R S T U V W X Y Z A B C 11/6/2017 Ciesar Cipher 19 Caesar Cipher Caesar Cipher transformation Example: 1. Encryption Process = Plain text K H O O R I U L H Q G h e l l o f r i e n d = E = C
- 20. 11/6/2017 Ciesar Cipher 20 Caesar Cipher K H O O R I U L H Q G Plain text Cipher text = Encryption process h e l l o f r i e n d Decryption process h e l l o f r i e n dPlain text = Key=Shift 3rd place alphabet C = E(p) = (p + k) mod (26) p = D(C) = (C – k) mod (26)