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Cryptography Data communications and networks Momina Tariq: 07030619-021 Ambreen Sohail: 07030619-007 1 Data Communications and Networks.

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Presentation on theme: "Cryptography Data communications and networks Momina Tariq: 07030619-021 Ambreen Sohail: 07030619-007 1 Data Communications and Networks."— Presentation transcript:

1 Cryptography Data communications and networks Momina Tariq: 07030619-021 Ambreen Sohail: 07030619-007 1 Data Communications and Networks

2 2 T OPICS Cryptography Components Types of cryptography Symmetric-key cryptography Asymmetric-key cryptography Traditional ciphers Substitution cipher Transposition cipher

3 Data Communications and Networks 3 C RYPTOGRAPHY Cryptography is the practice and study of hiding information. A field of mathematics and computer science concerned with information security and related issues, particularly encryption and authentication.

4 Data Communications and Networks 4 C OMPONENTS INVOLVED IN C RYPTOGRAPHY Plaintext - Text message to which an algorithm is applied Cipher text - Encrypted or scrambled message produced by applying the algorithm to the plaintext message using the secret key Cipher - A message written in a secret code Key - A key is a number or set of numbers that the cipher, as an algorithm, operates on

5 Data Communications and Networks 5 C OMPONENTS INVOLVED IN C RYPTOGRAPHY ( CONT.) Encryption: Creating cipher text from plaintext with a specific encryption algorithm and an encryption key Decryption: Covering plaintext from cipher text using a specific encryption algorithm and a decryption key

6 Data Communications and Networks 6 T YPES OF C RYPTOGRAPHY Symmetric-key cryptography / Secret-key cryptography Asymmetric-key cryptography / Public-key cryptography

7 Data Communications and Networks 7 S YMMETRIC - KEY CRYPTOGRAPHY An encryption system in which the sender and receiver of a message share a single, common key that is used to encrypt and decrypt the message Symmetric-key cryptography is sometimes called secret-key cryptography

8 Data Communications and Networks 8 S YMMETRIC - KEY CRYPTOGRAPHY

9 9 T RADITIONAL C IPHERS Two sub types of traditional ciphers: Substitution ciphers Transposition ciphers

10 Data Communications and Networks 10 S UBSTITUTION CIPHERS “ A substitution cipher substitutes one symbol with another. If the symbols in the plaintext are alphabetic characters, we replace one character with another.” Types of substitution ciphers Monoalphabetic cipher Polyalphabetic cipher

11 Data Communications and Networks 11 M ONOALPHABETIC S UBSTITUTION “In a monoalphabetic cipher, a character (or symbol) in the plaintext is always changed to the same character(or symbol) in the ciphertext regardless of its position in the text. It simply means one-to-one relationship”

12 Data Communications and Networks 12 M ONOALPHABETIC S UBSTITUTION

13 Data Communications and Networks 13 P OLYALPHABETIC C IPHERS A cipher that uses multiple substitution alphabets is called a polyalphabetic substitution cipher. The Vigenere Cipher and Hill Cipher are examples of alphabetic ciphers

14 Data Communications and Networks 14 T HE V IGENÈRE C IPHER The Vigenère Cipher makes use of a keyword of length m. So, First step: determine the key length=m, Second step: determine the key (word) itself After that encryption/decryption of the message is easy.

15 T HE V IGENÈRE C IPHER ( EXAMPLE ) Pthiscryptosy 197818217241519141824 K2815741728157417 21152325680238212215 CVPXZGIAXIVWP PstemisnotsecuRe 1819412818131419184220174 K28157417281574172815 20119 1291522825819222519 CUBTTMJPWIZITWZT 15 Data Communications and Networks Suppose key length (m)=6 Key word (K) = C I P H E R = (2,8,15,7,4,17) Plaintext (P) = thiscryptosystemisnotsecure Ciphertext (C) = VPXZGIAXIVWPUBTTMJPWIZITWZI

16 Data Communications and Networks 16 T HE V IGENÈRE T ABLE 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  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 A  C 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  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  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 D  F G H I J K L M N O P Q R S T U V W X Y Z A B C D E  G H I J K L M N O P Q R S T U V W X Y Z A B C D E F  H I J K L M N O P Q R S T U V W X Y Z A B C D E F G  I J K L M N O P Q R S T U V W X Y Z A B C D E F G H  J K L M N O P Q R S T U V W X Y Z A B C D E F G H I  K L M N O P Q R S T U V W X Y Z A B C D E F G H I J  L M N O P Q R S T U V W X Y Z A B C D E F G H I J K  M N O P Q R S T U V W X Y Z A B C D E F G H I J K L  N O P Q R S T U V W X Y Z A B C D E F G H I J K L M  O P Q R S T U V W X Y Z A B C D E F G H I J K L M N  P Q R S T U V W X Y Z A B C D E F G H I J K L M N O  Q R S T U V W X Y Z A B C D E F G H I J K L M N O P  R S T U V W X Y Z A B C D E F G H I J K L M N O P Q  S T U V W X Y Z A B C D E F G H I J K L M N O P Q R  T U V W X Y Z A B C D E F G H I J K L M N O P Q R S  U V W X Y Z A B C D E F G H I J K L M N O P Q R S T  V W X Y Z A B C D E F G H I J K L M N O P Q R S T U  W X Y Z A B C D E F G H I J K L M N O P Q R S T U V  X Y Z A B C D E F G H I J K L M N O P Q R S T U V W  Y Z A B C D E F G H I J K L M N O P Q R S T U V W X  Z 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

17 Data Communications and Networks 17 T RANSPOSITION C IPHER Methods of encryption by which the positions held by units of plaintext are shifted according to a regular system For example: Plaintext: V O Y A G E R Ciphertext: O V A Y E G R where every two letters are switched with each other

18 Data Communications and Networks 18 A SYMMETRIC -K EY C RYPTOGRAPHY A pair of keys is used. The sender uses the public key; the receiver uses the private key. Asymmetric-key cryptography is sometimes called Public-key cryptography

19 Data Communications and Networks 19 A SYMMETRIC - KEY C RYPTOGRAPHY

20 Data Communications and Networks 20 ANY QUESTIONS ? ? ?

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