Classical Encryption Techniques Introduction to Network Security Classical
![Classical Encryption Techniques Introduction to Network Security Classical Encryption Techniques Introduction to Network Security](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-1.jpg)
![Classical encryption techniques • Encryption : – Encryption is something like making a secret Classical encryption techniques • Encryption : – Encryption is something like making a secret](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-2.jpg)
![Basic terminology • Plaintext: original message to be encrypted • Ciphertext: the encrypted message Basic terminology • Plaintext: original message to be encrypted • Ciphertext: the encrypted message](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-3.jpg)
![Symmetric Cipher Model 4 Symmetric Cipher Model 4](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-4.jpg)
![• Deciphering or decryption: recovering plaintext from ciphertext • Decryption algorithm: performs decryption • Deciphering or decryption: recovering plaintext from ciphertext • Decryption algorithm: performs decryption](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-5.jpg)
![• Cipher or cryptographic system : a scheme for encryption and decryption • • Cipher or cryptographic system : a scheme for encryption and decryption •](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-6.jpg)
![Ciphers • Symmetric cipher: same key used for encryption and decryption – Block cipher: Ciphers • Symmetric cipher: same key used for encryption and decryption – Block cipher:](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-7.jpg)
![Symmetric Encryption • or conventional / secret-key / single-key • sender and recipient share Symmetric Encryption • or conventional / secret-key / single-key • sender and recipient share](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-8.jpg)
![Symmetric Encryption • Mathematically: • • • Y = EK(X) X = DK(Y) or Symmetric Encryption • Mathematically: • • • Y = EK(X) X = DK(Y) or](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-9.jpg)
![Cryptanalysis • Objective: to recover the plaintext of a ciphertext or, more typically, to Cryptanalysis • Objective: to recover the plaintext of a ciphertext or, more typically, to](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-10.jpg)
![Brute-Force Attack • Try every key to decipher the ciphertext. • On average, need Brute-Force Attack • Try every key to decipher the ciphertext. • On average, need](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-11.jpg)
![Cryptanalytic Attacks • May be classified by how much information needed by the attacker: Cryptanalytic Attacks • May be classified by how much information needed by the attacker:](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-12.jpg)
![Classical Ciphers • Plaintext is viewed as a sequence of elements (e. g. , Classical Ciphers • Plaintext is viewed as a sequence of elements (e. g. ,](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-13.jpg)
![Caesar Cipher • Earliest known substitution cipher • Invented by Julius Caesar • Ciphertext Caesar Cipher • Earliest known substitution cipher • Invented by Julius Caesar • Ciphertext](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-14.jpg)
![Caesar Cipher • Mathematically, map letters to numbers: a, b, c, . . . Caesar Cipher • Mathematically, map letters to numbers: a, b, c, . . .](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-15.jpg)
![Monoalphabetic Substitution Cipher • Shuffle the letters and map each plaintext letter to a Monoalphabetic Substitution Cipher • Shuffle the letters and map each plaintext letter to a](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-16.jpg)
![Playfair Cipher • • One approach to improving security is to encrypt multiple letters Playfair Cipher • • One approach to improving security is to encrypt multiple letters](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-17.jpg)
![Playfair Cipher • Rules: – If pair letters are same, add an X (uncommon Playfair Cipher • Rules: – If pair letters are same, add an X (uncommon](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-18.jpg)
![Playfair Key Matrix • • Use a 5 x 5 matrix. Fill in letters Playfair Key Matrix • • Use a 5 x 5 matrix. Fill in letters](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-19.jpg)
![Encrypting and Decrypting Plaintext is encrypted two letters at a time. 1. If a Encrypting and Decrypting Plaintext is encrypted two letters at a time. 1. If a](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-20.jpg)
![Hill Cipher • The algo takes n x n matrix. • The cipher C Hill Cipher • The algo takes n x n matrix. • The cipher C](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-21.jpg)
![Hill Cipher • Example : – Plaintext is “paymoremoney” and key is – K= Hill Cipher • Example : – Plaintext is “paymoremoney” and key is – K=](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-22.jpg)
![Hill Cipher • PAY = |15 0 24|, P = 15 • C = Hill Cipher • PAY = |15 0 24|, P = 15 • C =](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-23.jpg)
![Hill Cipher • C= 375 819 486 C= 11 L 13 N 18 S Hill Cipher • C= 375 819 486 C= 11 L 13 N 18 S](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-24.jpg)
![Polyalphabetic Substitution Ciphers • A sequence of monoalphabetic ciphers (M 1, M 2, M Polyalphabetic Substitution Ciphers • A sequence of monoalphabetic ciphers (M 1, M 2, M](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-25.jpg)
![Vigenère Cipher • Simplest polyalphabetic substitution cipher • Consider the set of all Caesar Vigenère Cipher • Simplest polyalphabetic substitution cipher • Consider the set of all Caesar](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-26.jpg)
![Example of Vigenère Cipher • Keyword: deceptive key: deceptivedeceptive plaintext: wearediscoveredsaveyourself ciphertext: ZICVTWQNGRZGVTWAVZHCQYGLMGJ 27 Example of Vigenère Cipher • Keyword: deceptive key: deceptivedeceptive plaintext: wearediscoveredsaveyourself ciphertext: ZICVTWQNGRZGVTWAVZHCQYGLMGJ 27](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-27.jpg)
![Security of Vigenère Ciphers • There are multiple (how many? ) ciphertext letters corresponding Security of Vigenère Ciphers • There are multiple (how many? ) ciphertext letters corresponding](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-28.jpg)
![Transposition Ciphers • Also called permutation ciphers. • Shuffle the plaintext, without altering the Transposition Ciphers • Also called permutation ciphers. • Shuffle the plaintext, without altering the](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-29.jpg)
![Row Transposition Ciphers • Plaintext is written row by row in a rectangle. • Row Transposition Ciphers • Plaintext is written row by row in a rectangle. •](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-30.jpg)
![Product Ciphers • Uses a sequence of substitutions and transpositions – Harder to break Product Ciphers • Uses a sequence of substitutions and transpositions – Harder to break](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-31.jpg)
![Unconditional & Computational Security • A cipher is unconditionally secure if it is secure Unconditional & Computational Security • A cipher is unconditionally secure if it is secure](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-32.jpg)
![An unconditionally Secure Cipher 33 An unconditionally Secure Cipher 33](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-33.jpg)
![Steganography • Hide a message in another message. • E. g. , hide your Steganography • Hide a message in another message. • E. g. , hide your](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-34.jpg)
![• Take a 640 x 480 (=30, 7200) pixel image. • Using only • Take a 640 x 480 (=30, 7200) pixel image. • Using only](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-35.jpg)
![36 36](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-36.jpg)
![Summary • Have considered: – classical cipher techniques and terminology – monoalphabetic substitution ciphers Summary • Have considered: – classical cipher techniques and terminology – monoalphabetic substitution ciphers](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-37.jpg)
- Slides: 37
![Classical Encryption Techniques Introduction to Network Security Classical Encryption Techniques Introduction to Network Security](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-1.jpg)
Classical Encryption Techniques Introduction to Network Security
![Classical encryption techniques Encryption Encryption is something like making a secret Classical encryption techniques • Encryption : – Encryption is something like making a secret](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-2.jpg)
Classical encryption techniques • Encryption : – Encryption is something like making a secret letter by changing, swapping or replacing characters in previously defend order. The format of the message is not changed. • Encoding : – In coding the format of data is changed. For example we record a voice sample, the recorder will encode the analog voice signals into digital signals & store. 2
![Basic terminology Plaintext original message to be encrypted Ciphertext the encrypted message Basic terminology • Plaintext: original message to be encrypted • Ciphertext: the encrypted message](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-3.jpg)
Basic terminology • Plaintext: original message to be encrypted • Ciphertext: the encrypted message • Enciphering or encryption: the process of converting plaintext into ciphertext • Encryption algorithm: performs encryption – Two inputs: a plaintext and a secret key 3
![Symmetric Cipher Model 4 Symmetric Cipher Model 4](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-4.jpg)
Symmetric Cipher Model 4
![Deciphering or decryption recovering plaintext from ciphertext Decryption algorithm performs decryption • Deciphering or decryption: recovering plaintext from ciphertext • Decryption algorithm: performs decryption](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-5.jpg)
• Deciphering or decryption: recovering plaintext from ciphertext • Decryption algorithm: performs decryption – Two inputs: ciphertext and secret key • Secret key: same key used for encryption and decryption – Also referred to as a symmetric key 5
![Cipher or cryptographic system a scheme for encryption and decryption • Cipher or cryptographic system : a scheme for encryption and decryption •](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-6.jpg)
• Cipher or cryptographic system : a scheme for encryption and decryption • Cryptography: science of studying ciphers • Cryptanalysis: science of studying attacks against cryptographic systems • Cryptology: cryptography + cryptanalysis 6
![Ciphers Symmetric cipher same key used for encryption and decryption Block cipher Ciphers • Symmetric cipher: same key used for encryption and decryption – Block cipher:](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-7.jpg)
Ciphers • Symmetric cipher: same key used for encryption and decryption – Block cipher: encrypts a block of plaintext at a time (typically 64 or 128 bits) – Stream cipher: encrypts data one bit or one byte at a time • Asymmetric cipher: different keys used for encryption and decryption 7
![Symmetric Encryption or conventional secretkey singlekey sender and recipient share Symmetric Encryption • or conventional / secret-key / single-key • sender and recipient share](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-8.jpg)
Symmetric Encryption • or conventional / secret-key / single-key • sender and recipient share a common key • all classical encryption algorithms are symmetric 8
![Symmetric Encryption Mathematically Y EKX X DKY or Symmetric Encryption • Mathematically: • • • Y = EK(X) X = DK(Y) or](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-9.jpg)
Symmetric Encryption • Mathematically: • • • Y = EK(X) X = DK(Y) or or Y = E(K, X) X = D(K, Y) X = plaintext Y = ciphertext K = secret key E = encryption algorithm D = decryption algorithm Both E and D are known to public 9
![Cryptanalysis Objective to recover the plaintext of a ciphertext or more typically to Cryptanalysis • Objective: to recover the plaintext of a ciphertext or, more typically, to](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-10.jpg)
Cryptanalysis • Objective: to recover the plaintext of a ciphertext or, more typically, to recover the secret key. • Kerkhoff’s principle: the opponent knows all details about a cryptosystem except the secret key. • Two general approaches: – brute-force attack – non-brute-force attack (cryptanalytic attack) 10
![BruteForce Attack Try every key to decipher the ciphertext On average need Brute-Force Attack • Try every key to decipher the ciphertext. • On average, need](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-11.jpg)
Brute-Force Attack • Try every key to decipher the ciphertext. • On average, need to try half of all possible keys • Time needed proportional to size of key space Key Size (bits) Number of Alternative Keys Time required at 1 decryption/µs Time required at 106 decryptions/µs 32 232 = 4. 3 109 231 µs = 35. 8 minutes 2. 15 milliseconds 56 256 = 7. 2 1016 255 µs = 1142 years 10. 01 hours 128 2128 = 3. 4 1038 2127 µs = 5. 4 1024 years 5. 4 1018 years 168 2168 = 3. 7 1050 2167 µs = 5. 9 1036 years 5. 9 1030 years 26! = 4 1026 2 1026 µs = 6. 4 1012 years 26 characters (permutation) 6. 4 106 years 11
![Cryptanalytic Attacks May be classified by how much information needed by the attacker Cryptanalytic Attacks • May be classified by how much information needed by the attacker:](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-12.jpg)
Cryptanalytic Attacks • May be classified by how much information needed by the attacker: – Ciphertext-only attack – Known-plaintext attack – Chosen-ciphertext attack 12
![Classical Ciphers Plaintext is viewed as a sequence of elements e g Classical Ciphers • Plaintext is viewed as a sequence of elements (e. g. ,](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-13.jpg)
Classical Ciphers • Plaintext is viewed as a sequence of elements (e. g. , bits or characters) • Substitution cipher: replacing each element of the plaintext with another element. • Transposition (or permutation) cipher: rearranging the order of the elements of the plaintext. 13
![Caesar Cipher Earliest known substitution cipher Invented by Julius Caesar Ciphertext Caesar Cipher • Earliest known substitution cipher • Invented by Julius Caesar • Ciphertext](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-14.jpg)
Caesar Cipher • Earliest known substitution cipher • Invented by Julius Caesar • Ciphertext is derived from the plaintext alphabet by shifting each letter a certain number of spaces. • Each letter is replaced by the letter three positions further down the alphabet. • Plain: 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 Cipher: 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 • Example: Meet me after the tea party phhw ph diwhu wkh sduwb 14
![Caesar Cipher Mathematically map letters to numbers a b c Caesar Cipher • Mathematically, map letters to numbers: a, b, c, . . .](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-15.jpg)
Caesar Cipher • Mathematically, map letters to numbers: a, b, c, . . . , x, y, z 0, 1, 2, . . . , 23, 24, 25 • Then the general Caesar cipher is: c = EK(p) = (p + k) mod 26 p = DK(c) = (c – k) mod 26 • Can be generalized with any alphabet. 15
![Monoalphabetic Substitution Cipher Shuffle the letters and map each plaintext letter to a Monoalphabetic Substitution Cipher • Shuffle the letters and map each plaintext letter to a](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-16.jpg)
Monoalphabetic Substitution Cipher • Shuffle the letters and map each plaintext letter to a different random ciphertext letter: Plain letters: abcdefghijklmnopqrstuvwxyz Cipher letters: DKVQFIBJWPESCXHTMYAUOLRGZN Plaintext: ifwewishtoreplaceletters Ciphertext: WIRFRWAJUHYFTSDVFSFUUFYA • What does a key look like? 16
![Playfair Cipher One approach to improving security is to encrypt multiple letters Playfair Cipher • • One approach to improving security is to encrypt multiple letters](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-17.jpg)
Playfair Cipher • • One approach to improving security is to encrypt multiple letters at a time. • The Playfair Cipher is the best known such cipher. • Invented by Charles Wheatstone in 1854, but named after his friend Baron Playfair. • Simplest substitution cipher with two letters combination. • Encryption algo takes 5 x 5 matrix of letters. • Generate the key table. (drop any duplicate letter). • Key alphabets are filled in matrix from left to right & top to bottom. • Rest of the letters are filled in matrix in remaining spaces. • Letters I & j takes the same place. 17
![Playfair Cipher Rules If pair letters are same add an X uncommon Playfair Cipher • Rules: – If pair letters are same, add an X (uncommon](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-18.jpg)
Playfair Cipher • Rules: – If pair letters are same, add an X (uncommon letter) after the first letter. • Balloon will be (ba lx lo on). – If the letter appear in same row / column of the table, replace them with the letter to immediate right respectively. – If the letters are not on same row or column , replace with letter in the corners of rectangle.
![Playfair Key Matrix Use a 5 x 5 matrix Fill in letters Playfair Key Matrix • • Use a 5 x 5 matrix. Fill in letters](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-19.jpg)
Playfair Key Matrix • • Use a 5 x 5 matrix. Fill in letters of the key (w/o duplicates). Fill the rest of matrix with other letters. E. g. , key = MONARCHY. M O N A R C H Y B D E F G I/J K L P Q S T U V W X Z 19
![Encrypting and Decrypting Plaintext is encrypted two letters at a time 1 If a Encrypting and Decrypting Plaintext is encrypted two letters at a time. 1. If a](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-20.jpg)
Encrypting and Decrypting Plaintext is encrypted two letters at a time. 1. If a pair is a repeated letter, insert filler like 'X’. 2. If both letters fall in the same row, replace each with the letter to its right (circularly). 3. If both letters fall in the same column, replace each with the letter below it (circularly). 4. Otherwise, each letter is replaced by the letter in the same row but in the column of the other letter of the pair. 20
![Hill Cipher The algo takes n x n matrix The cipher C Hill Cipher • The algo takes n x n matrix. • The cipher C](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-21.jpg)
Hill Cipher • The algo takes n x n matrix. • The cipher C of P derived by multiplying P by K. • When decrypt the message the inverse of K is used. • C=(KP) mod (26) • P= K-1 C mod (26)
![Hill Cipher Example Plaintext is paymoremoney and key is K Hill Cipher • Example : – Plaintext is “paymoremoney” and key is – K=](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-22.jpg)
Hill Cipher • Example : – Plaintext is “paymoremoney” and key is – K= |17 17 5 | |21 18 21| |2 2 19| – 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 – ABCDEFGHIJ K L M N O P Q R S T – 20 21 22 23 24 25 – U VW X Y Z – KEY PAY MOR EMO NEY
![Hill Cipher PAY 15 0 24 P 15 C Hill Cipher • PAY = |15 0 24|, P = 15 • C =](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-23.jpg)
Hill Cipher • PAY = |15 0 24|, P = 15 • C = (KP) mod 26 0 24 C = 17 17 5 15 21 18 21 X 0 2 2 19 24 C= 255+0+120 315+0+504 mod 26 30+0+456 mod 26
![Hill Cipher C 375 819 486 C 11 L 13 N 18 S Hill Cipher • C= 375 819 486 C= 11 L 13 N 18 S](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-24.jpg)
Hill Cipher • C= 375 819 486 C= 11 L 13 N 18 S PAY = LNS mod 26
![Polyalphabetic Substitution Ciphers A sequence of monoalphabetic ciphers M 1 M 2 M Polyalphabetic Substitution Ciphers • A sequence of monoalphabetic ciphers (M 1, M 2, M](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-25.jpg)
Polyalphabetic Substitution Ciphers • A sequence of monoalphabetic ciphers (M 1, M 2, M 3, . . . , Mk) is used in turn to encrypt letters. • A key determines which sequence of ciphers to use. • Each plaintext letter has multiple corresponding ciphertext letters. • This makes cryptanalysis harder since the letter frequency distribution will be flatter. 25
![Vigenère Cipher Simplest polyalphabetic substitution cipher Consider the set of all Caesar Vigenère Cipher • Simplest polyalphabetic substitution cipher • Consider the set of all Caesar](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-26.jpg)
Vigenère Cipher • Simplest polyalphabetic substitution cipher • Consider the set of all Caesar ciphers: { Ca, Cb, Cc, . . . , Cz } • Key: e. g. security • Encrypt each letter using Cs, Ce, Cc, Cu, Cr, Ci, Ct, Cy in turn. • Repeat from start after Cy. • Decryption simply works in reverse. 26
![Example of Vigenère Cipher Keyword deceptive key deceptivedeceptive plaintext wearediscoveredsaveyourself ciphertext ZICVTWQNGRZGVTWAVZHCQYGLMGJ 27 Example of Vigenère Cipher • Keyword: deceptive key: deceptivedeceptive plaintext: wearediscoveredsaveyourself ciphertext: ZICVTWQNGRZGVTWAVZHCQYGLMGJ 27](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-27.jpg)
Example of Vigenère Cipher • Keyword: deceptive key: deceptivedeceptive plaintext: wearediscoveredsaveyourself ciphertext: ZICVTWQNGRZGVTWAVZHCQYGLMGJ 27
![Security of Vigenère Ciphers There are multiple how many ciphertext letters corresponding Security of Vigenère Ciphers • There are multiple (how many? ) ciphertext letters corresponding](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-28.jpg)
Security of Vigenère Ciphers • There are multiple (how many? ) ciphertext letters corresponding to each plaintext letter. • So, letter frequencies are obscured but not totally lost. • To break Vigenere cipher: 1. Try to guess the key length. How? 2. If key length is N, the cipher consists of N Caesar ciphers. Plaintext letters at positions k, N+k, 2 N+k, 3 N+k, etc. , are encoded by the same cipher. 3. Attack each individual cipher as before. 28
![Transposition Ciphers Also called permutation ciphers Shuffle the plaintext without altering the Transposition Ciphers • Also called permutation ciphers. • Shuffle the plaintext, without altering the](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-29.jpg)
Transposition Ciphers • Also called permutation ciphers. • Shuffle the plaintext, without altering the actual letters used. • Example: Row Transposition Ciphers 29
![Row Transposition Ciphers Plaintext is written row by row in a rectangle Row Transposition Ciphers • Plaintext is written row by row in a rectangle. •](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-30.jpg)
Row Transposition Ciphers • Plaintext is written row by row in a rectangle. • Ciphertext: write out the columns in an order specified by a key. Key: 3 4 2 1 5 6 7 a t t a c k p o s t p o n e Plaintext: d u n t i l t wo a mx y z Ciphertext: TTNAAPTMTSUOAODWCOIXKNLYPETZ 30
![Product Ciphers Uses a sequence of substitutions and transpositions Harder to break Product Ciphers • Uses a sequence of substitutions and transpositions – Harder to break](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-31.jpg)
Product Ciphers • Uses a sequence of substitutions and transpositions – Harder to break than just substitutions or transpositions • This is a bridge from classical to modern ciphers. 31
![Unconditional Computational Security A cipher is unconditionally secure if it is secure Unconditional & Computational Security • A cipher is unconditionally secure if it is secure](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-32.jpg)
Unconditional & Computational Security • A cipher is unconditionally secure if it is secure no matter how much resources (time, space) the attacker has. • A cipher is computationally secure if the best algorithm for breaking it will require so much resources (e. g. , 1000 years) that practically the cryptosystem is secure. • All the ciphers we have examined are not unconditionally secure. 32
![An unconditionally Secure Cipher 33 An unconditionally Secure Cipher 33](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-33.jpg)
An unconditionally Secure Cipher 33
![Steganography Hide a message in another message E g hide your Steganography • Hide a message in another message. • E. g. , hide your](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-34.jpg)
Steganography • Hide a message in another message. • E. g. , hide your plaintext in a graphic image – Each pixel has 3 bytes specifying the RGB color – The least significant bits of pixels can be changed w/o greatly affecting the image quality – So can hide messages in these LSBs • Advantage: hiding existence of messages • Drawback: high overhead 34
![Take a 640 x 480 30 7200 pixel image Using only • Take a 640 x 480 (=30, 7200) pixel image. • Using only](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-35.jpg)
• Take a 640 x 480 (=30, 7200) pixel image. • Using only 1 LSB, can hide 115, 200 characters • Using 4 LSBs, can hide 460, 800 characters. 35
![36 36](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-36.jpg)
36
![Summary Have considered classical cipher techniques and terminology monoalphabetic substitution ciphers Summary • Have considered: – classical cipher techniques and terminology – monoalphabetic substitution ciphers](https://slidetodoc.com/presentation_image_h2/62c56060b35d6c64359b1b20c4a26460/image-37.jpg)
Summary • Have considered: – classical cipher techniques and terminology – monoalphabetic substitution ciphers – cryptanalysis using letter frequencies – Playfair cipher – polyalphabetic ciphers – transposition ciphers – product ciphers and rotor machines – stenography 37
486 mod 26
Classical encryption techniques
Classical encryption techniques in cryptography
Security private
Osi security architecture model
Security guide to network security fundamentals
Wireless security in cryptography and network security
Electronic mail security in network security
Security guide to network security fundamentals
Security guide to network security fundamentals
Security mechanisms in cryptography
Introduction to cryptography and network security
Introduction to cryptography and network security
Food plating basics
Fonctions techniques
What is personnel security
"security techniques"
Explain about visa international security mode
Information security
Integrity in e commerce
Software security building security in
Network techniques for project management
Network traffic management techniques
Network traffic monitoring techniques
Network planning techniques
Network model in quantitative techniques
Network reliability and security
Wireless security definition
Palo alto certified network security engineer
Network security protocols
William stallings network security essentials 5th edition
Intruders in cryptography
Network design and implementation
Module 3: information and network security
Requirements of message authentication code
Network security protocols
Open systems nsm network security monitoring
Gfi languard network scanner