Superficial Study on the Concept of Cryptography
Upcoming SlideShare
Loading in...5
×
 

Like this? Share it with your network

Share

Superficial Study on the Concept of Cryptography

on

  • 431 views

Superficial Study on the Concept of Cryptography covering different types of ciphers

Superficial Study on the Concept of Cryptography covering different types of ciphers

Statistics

Views

Total Views
431
Views on SlideShare
431
Embed Views
0

Actions

Likes
0
Downloads
7
Comments
0

0 Embeds 0

No embeds

Accessibility

Categories

Upload Details

Uploaded via as Microsoft PowerPoint

Usage Rights

© All Rights Reserved

Report content

Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
  • Full Name Full Name Comment goes here.
    Are you sure you want to
    Your message goes here
    Processing…
Post Comment
Edit your comment

Superficial Study on the Concept of Cryptography Presentation Transcript

  • 1. Cryptography: A Brief Overview •Abhishek Gautam •Ashim Gurung •Bikram Koirala • Monil Adhikari
  • 2. Agenda Classical Cryptography coverage(esp. Substitution Ciphers): Mono-alphabetic Substitution Ciphers. Homophonic Substitution Ciphers. Poly-graphic Substitution Ciphers. Poly-alphabetic Substitution Ciphers.
  • 3. Substitution Ciphers • Introduction Substitution Ciphers are the ciphers where a alphabet is replaced by another different ciphers. This ciphers mainly uses the alphabets to encrypt messages for confidentiality in communication.
  • 4. Mono-alphabetic Ciphers • The Mono-alphabetic Substitution cipher is where each character in the plaintext is replaced by a corresponding one from a cipher alphabet. There are 3 types of Mono-alphabetic Ciphers. – 1) Caesar Ciphers – 2) Affine Ciphers – 3) Atbash Ciphers
  • 5. Caesar Ciphers • This is a video which briefly describes about the working of a Caesar ciphers. (Youtube,2012)
  • 6. Homophonic Ciphers • A homophonic substitution cipher maps each plaintext letter of a message to one or more cipher text symbols. Homophonic ciphers hide letter frequencies of plaintext messages which are mapped to one or more cipher text units called homophones. • This method is based on the mono alphabetic substitution. The original text is not only encrypted by one but is also replaced with multiple secret symbols.
  • 7. Homophonic Ciphers(Contd.) • • A Homophonic substitution cipher is like a simple substitution cryptosystem, in which a single character of plaintext can map to one of several characters of cipher text. A plaintext message M=m1m2... is enciphered as C=c1c2..., where each ci is picked at random from the set of homophones f(mi). Letter Homophones A 17 19 34 41 56 60 67 83 I 08 22 53 65 88 90 L 03 44 76 N 02 09 15 27 32 40 59 O 01 11 23 28 42 54 70 80 P 33 91 T 05 10 20 29 45 58 64 78 99 One possible encipherment of the message is: M=P L A I N P I L O T C = 91 44 56 65 59 33 08 76 28 78
  • 8. Poly-graphic Ciphers • “In a polygraphic substitution cipher plaintext letters are substituted in large groups instead of substituting letters individually”.(wordIQ, n.d) • The first advantage is that the frequency distribution is much flatter than that of individual letter. • Second , the large numbers of symbols requires correspondingly more cipher text to productively analyze letter frequencies.
  • 9. Playfair Ciphers • The playfair cipher encrypts pair of letters(diagraph), instead of single letters. • It was invented in 1854 by Charles Wheatstone for telegraph secrecy. • It is the earliest practical Polygraphic Substitution ciphers. • The cipher used a 5 by five table containing a key word.
  • 10. Poly-alphabetic Ciphers • In poly-alphabetic cipher, each plaintext character may be replaced by more than one character • Since there are only 26 alphabets this process will require using a different representation than the alphabets • Alphabets „A‟ through „Z‟ are replaced by 00, 01, 02, …, 25 • We need two digits in this representation since we need to know how to reverse the process at the decryption side (Babylon,1997).
  • 11. Vignere Ciphers • The most common method used as a type of Poly-Alphabetic Cipher is Vigenère cipher • Vigenère cipher starts with a 26 x 26 matrix of alphabets in sequence. First row starts with „A‟, second row starts with „B‟, etc.
  • 12. Vigenere(Contd.) • E.g., Message = SEE ME IN MALL • Take keyword as INFOSEC • Vigenère cipher works as follows: SEEME I NMALL I NFOSEC I NFO ------------------------------------A RJ AWMPUNQZ
  • 13. Conclusion • We have considered mainly the key aspects of Substitution Ciphers and their workings as well as their algorithms.
  • 14. References • Brown, 1996, Introduction to Cryptography, [online], Available at: http://williamstallings.com/Extras/Security-Notes/lectures/classical.html [Accessed at 1st Jan 2012] • All Science Projects, 2011, [online], Available at: http://www.all-science-fairprojects.com/science_fair_projects_encyclopedia/Caesar_cipher [Accessed at 1 Jan 2012] • Chargrill, 2006,PlayFair Cipher ,[online] http://www.perlmonks.org/?node_id=554404 accessed on Jan 11 • WordIQ, n.d, Substitution cipher- Definition, [online] http://www.wordiq.com/definition/Substitution_cipher#Polygraphic_substitution accessed on Jan 11 • University of Adelaide,2012,[online],Available at : https://www.eleceng.adelaide.edu.au/personal/dabbott/wiki/index.php/Cipher_Crossoff_List#Homophonic_Substitution_Ciphers,[Accessed on 10 Jan 2012] • Mrgeorged, 2009. Top Gear The Stig revealed Full. [video online],Available at:<http://www.youtube.com/watch#!v=eTapK5dRaw4>[Accessed 23 June 2009].