(BPE3723) Module 2 Cryptograpy.pdf

Introduction to Computer Network and Security (BPE3723) Module 2: Cryptography  Cryptography [1/5]  The art or science encompassing the principles and methods of transforming an intelligible message into one that is...

Introduction to Computer Network and Security (BPE3723) Module 2: Cryptography  Cryptography [1/5]  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  Terminology Plaintext The original intelligible message Cipher text The transformed message Cipher An algorithm for transforming an intelligible message into one that is unintelligible by transposition and/or substitution methods Key Some critical information used by the cipher, known only to the sender& receiver Encipher (encode) The process of converting plaintext to cipher text using a cipher and a key Decipher (decode) the process of converting cipher text back into plaintext using a cipher and a key Cryptanalysis The study of principles and methods of transforming an unintelligible message back into an intelligible message without knowledge of the key. Also called code breaking Cryptology Both cryptography and cryptanalysis Code An algorithm for transforming an intelligible message into an unintelligible one using a code-book  Cryptography [2/5]  Cryptographic systems are generally classified along 3 independent dimensions: i. Type of operations used for transforming plain text to cipher text All the encryption algorithms are based on two general principles: substitution, in which each element in the plaintext is mapped into another element, and transposition, in which elements in the plaintext are rearranged. ii. Type of operations used for transforming plain text to cipher text If the sender and receiver uses same key then it is said to be symmetric key (or) single key (or) conventional encryption. If the sender and receiver use different keys then it is said to be public key encryption. iii. The way in which the plain text is processed If A block cipher processes the input and block of elements at a time, producing output block for each input block. A stream cipher processes the input elements continuously, producing output element one at a time, as it goes along.  Cryptography [3/5]  Cryptography began primarily as a way for two parties - “Andy” and “Sam,” to communicate securely even if their messages might be read by an eavesdropper, “Eaves.”  Examples of current applications of cryptography include attesting the identity of the organization operating a web server, digitally signing electronic documents, protecting the confidentiality of online baking and shopping transactions, protecting the confidentiality of the files stored on a hard drive, and protecting the confidentiality of packets sent over a wireless network.  Cryptography deals with many techniques for secure and trustworthy communication and computation. Cryptography [4/5]  Cryptography [5/5]  Cryptography is broadly classified into 2 categories: Symmetric key Cryptographic and Asymmetric key Cryptography  Symmetric Key Cryptography [1/5]  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. The most popular symmetric–key system is the Data Encryption Standard (DES)  Symmetric or secret-key encryption algorithm that encrypts a single bit at a time  Symmetric Key Cryptography [2/5] Classical Cryptography  Transposition Ciphers - a method of encryption by which the positions held by units of plaintext (which are commonly characters or groups of characters) are shifted according to a regular system, so that the ciphertext constitutes a permutation of the plaintext.  Symmetric Key Cryptography [3/5] Classical Cryptography  Substitution Ciphers - method of encryption by which units of plaintext are replaced with ciphertext, according to a fixed system; the “units” may be single letters (the most common), pairs of letters, triplets of letters, mixtures of the above, and so forth  Symmetric Key Cryptography [4/5] Modern Cryptography  Stream Ciphers - the same plaintext bit or byte will encrypt to a different bit or byte every time it is encrypted  Symmetric Key Cryptography [5/5] Modern Cryptography  Block Ciphers - an encryption method that applies a deterministic algorithm along with a symmetric key to encrypt a block of text, rather than encrypting one bit at a time as in stream ciphers  Asymmetric Key Cryptography [1/2]  The encryption process where different keys are used for encrypting and decrypting the information. Keys are different but are mathematically related, such that retrieving the plain text by decrypting ciphertext is feasible.  The most widely used - RSA  Asymmetric Key Cryptography [2/2]  RSA Algorithm Rivest, Shamir and Adelman – the inventors of this technique Both public and private key are interchangeable Variable key size (512, 1024, or 2048 bits) Thanks