There are many aspects to security and many appli cations, Cryptography and network security 1. Slideshare uses cookies to improve functionality and performance, and to provide you with relevant advertising. SECURITY SECURITY THREATS SECURITY GOALS WHAT IS CRYPTOGRAPHY BASIC TERMS ENCRYPTION & DECRYPTION CATEGORIES OF CYRPTOGRAPHY COMPARISON CONCLUSION ... Cryptography and network security patisa. CRYPTOGRAPHY PRATIKSHA PATIL 2. If you continue browsing the site, you agree to the use of cookies on this website. All Rights Reserved. | PowerPoint PPT presentation | free to view Boston U. If you continue browsing the site, you agree to the use of cookies on this website. Cryptography and Network SecurityChapter 3. Stallings = Cryptography and Network Security, by William Stallings, 3 rd Edition, Prentice Hall, 2003. KUSUM SHARMA M.Sc S/W 2. by William Stallings Lecture slides by Lawrie Brown. Model for Network Security using this model requires us to: 1. design a suitable algorithm for the security transformation 2. generate the secret information (keys) used by the algorithm 3. develop methods to distribute and share the secret information 4. specify a protocol enabling the principals to use the transformation and secret information for a security service Rose-Hulman Institute of Technology. 4. if a pair is a repeated letter, insert filler like 'X' if both letters fall in the same row, replace each with letter to right (wrapping back to start from end) if both letters fall in the same column, replace each with the letter below it (wrapping to top from bottom) otherwise each letter is replaced by the letter in the same row and in the column of the other letter of the pair, Security of Playfair Cipher security much improved over monoalphabetic since have 26 x 26 : 676 digrams would need a 676 entry frequency table to analyse (verses 26 for a monoalphabetic) and correspondingly more ciphertext was widely used for many years ego by US & British military in WW1 it can be broken, given a few hundred letters since still has much of plaintext structure, Polyalphabetic Ciphers polyalphabetic substitution ciphers improve security using multiple cipher alphabets make cryptanalysis harder with more alphabets to guess and flatter frequency distribution use a key to select which alphabet is used for each letter of the message use each alphabet in turn repeat from start after end of key is reached, Vigenåre Cipher o simplest polyalphabetic substitution cipher o effectively multiple caesar ciphers o key is multiple letters long K kl kd o ith letter specifies ith alphabet to use 0 use each alphabet in turn o repeat from start after d letters in message o decryption simply works in reverse, Example of Vigenåre Cipher write the plaintext out write the keyword repeated above it use each key letter as a caesar cipher key encrypt the corresponding plaintext letter eg using keyword deceptive plaintext: wearediscoveredsaveyourself ciphertext : ZICVTWQNGRZGVTWAVZHCQYGLMGJ, Vigenère Cipher Table ABCDEFGHIJKLMNOPQRSTUVWXYZ ABCDEFGHIJKLMNOPQRSTUVWXYZ A B ABCDEFGHIJKLMNOPQRSTUVWXY B CDEFGHIJKLMNOPQRSTUVWXYZAB c DEFGHIJKLMNOPQRSTUVWXYZABC E EFGHIJKLMNOPQRSTUVWXYZABCD FGHIJKLMNOPQRSTUVWXYZABCDE F GGHIJKLMNOPQRSTUVWXYZABCDEF HIJKLMNOPQRSTUVWXYZABCDEFG H IJKLMNOPQRSTUVWXYZABCDEFGH 1 JJKLMNOPQRSTUVWXYZABCDEFGHI KLMNOPQRSTUVWXYZABCDEFGHIJ K LLMNOPQRSTUVWXYZABCDEFGHIJK MMNOPQRSTUVWXYZABCDEFGHIJKL 29, Vigenčre Cipher Table (conťd) ABC DEF GHIJKLMNOPQRSTUVWXYZ NOPQRSTUVWXYZABCDEFGHIJKLM N OPQRSTUVWXYZABCDEFGHIJKLMN o PQRSTUVWXYZABCDEFGHIJKLMNO QQRSTUVWXYZABCDEFGHIJKLMNOP RRSTUVWXYZABCDEFGHIJKLMNOPQ SSTUVWXYZABCDEFGHIJKLMNOPQR TTUVWXYZABCDEFGHIJKLMNOPQRS UUVWXYZABCDEFGHIJKLMNOPQRST V VWXYZABCDEFGHIJKLMNOPQRSTU WXYZABCDEFGHIJKLMNOPQRSTUV XXYZABCDEFGHIJKLMNOPQRSTUVW YYZABCDEFGHIJKLMNOPQRSTUVWX Z ZABCDEFGHIJKLMNOPQRSTUVWXY 30, Polyalphabetic Cipher E.g., Message = SEE ME IN MALL Take keyword as INFOSEC Vigen&re cipher works as follows: 1 NFOSECINFO ARJAWMPUNQZ 31, Polyalphabetic Cipher To decrypt, the receiver places the keyword characters below each ciphertext character Using the table, choose the row corresponding to the keyword character and look for the ciphertext character in that row Plaintext character is then at the top of that column 32, Polyalphabetic Cipher Decryption of ciphertext: ARJ AWMPUNQZ INFO SEC INFO SEEM EIN MALL Best feature is that same plaintext character is substituted by different ciphertext characters (i.e., polyalphabetic) 33, Security of Vigenåre Ciphers o have multiple ciphertext letters for each plaintext letter 0 hence letter frequencies are obscured o but not totally lost 0 start with letter frequencies o see if look monoalphabetic or not 0 if not, then need to determine number of alphabets, since then can attach each, Autokey Cipher o ideally want a key as long as the message o Vigen&re proposed the autokey cipher o with keyword is prefixed to message as key o knowing keyword can recover the first few letters 0 use these in turn on the rest of the message o but still have frequency characteristics to attack o ego given key deceptive deceptivewearediscoveredsav plaintext: wearediscoveredsaveyourself ciphertext : Z ICVTWQNGKZEI IGASXSTSLVVWLA, Vernam Cipher ultimate defense is to use a key as long as the plaintext with no statistical relationship to it invented by AT&T engineer Gilbert Vernam in 1918 originally proposed using a very long but eventually repeating key, One-Time Pad o if a truly random key as long as the message is used, the cipher will be secure o called a One-Time pad o is unbreakable since ciphertext bears no statistical relationship to the plaintext 0 since for any plaintext & any ciphertext there exists a key mapping one to other o can only use the key once though o problems in generation & safe distribution of key, Transposition Ciphers now consider classical transposition or permutation ciphers these hide the message by rearranging the letter order without altering the actual letters used can recognise these since have the same frequency distribution as the original text, Rail Fence cipher 0 write message letters out diagonally over a number of rows o then read off cipher row by row 0 ego write message out as: me m atr h t g pry o giving ciphertext MEMATRHTGPRYETEFETEOAAT, Row Transposition Ciphers is a more complex transposition write letters of messaqe out in rows over a specified number of columns then reorder the columns according to some key before reading off the rows Key: 4312567 Column Out Plaintext : Cipher text : 3421567 attack p o st pone dun tilt w oa m xyz TTNAAPTMTSUOAODWCOIXKNLYPETZ, Row Transposition Ciphers 0 Plaintext is written row by row in a rectangle. Common terms and phrases. CIS433 533 Computer and Network Security Cryptography. | PowerPoint PPT presentation | free to view Notes: KPS = Network Security - Private Communication in a Public World, by Charlie Kaufman, Radia Perlman and Mike Speciner, 2nd Edition, Prentice Hall, 2002. o Ciphertext: write out the columns in an order specified by a key. Cryptography and Network Security. See our User Agreement and Privacy Policy. This edition also provides a website that includes Powerpoint files as well as instructor and students solutions manuals. Fifth Edition by William Stallings, 3 rd Edition, Prentice Hall,.. Seminar and PPT with pdf report will increase your profile visibility, please upload on MyPrivateTutor columns in order... Presentation & Seminar Ad hoc networks do not have a fixed Network.... … Cryptography and Network SecurityChapter 3 of Puerto Rico and students solutions manuals & Network Security.ppt want to back! 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