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Symmetric Encryption. or conventional / private-key / single-key ender and recipient share a common key all classical encryption algorithms are private-key was only type prior to invention of public-key in 1970’s. The General Idea of Symmetric-Key Cryptography. Classic ciphers.
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Symmetric Encryption • or conventional / private-key / single-key • ender and recipient share a common key • all classical encryption algorithms are private-key • was only type prior to invention of public-key in 1970’s
Classic ciphers • substitution ciphers • monoalphabetic ciphers • polyalphabetic ciphers • transposition (permutation) ciphers • product ciphers • using both • substitution, and • transposition
Classical Cryptography • Monoalphabetic CiphersOnce a key is chosen, each alphabetic character of a plaintext is mapped onto a uniquealphabetic character of a ciphertext. • The Shift Cipher (Caesar Cipher) • The Substitution Cipher • The Affine Cipher
Classical Cryptography • Polyalphabetic CiphersEach alphabetic character of a plaintext can be mapped onto malphabetic characters of a ciphertext. Usually m is related to the encryption key. • The Vigenère Cipher • The Hill Cipher • The Permutation Cipher
Benefits of Cryptography • Offers individual privacy and confidentiality. • In some circumstances also authentication and non-repudiation (e.g. legal ‘signatures’) • Especially important in explicitly Authorization .
Cryptanalysis • Is the science and study of methods of breaking ciphers. A cipher is breakable if it is possible to determine the plaintext or key from the Cipher text or to determine the key from both plaintext and Cipher text
Types of Cryptanalysis attacks • 1. Ciphertext-only attack:- • The cryptanalyst has the cipher text of several messages, all of which have been encrypted using the same encryption algorithm, the cryptanalyst job is to recover the plain text of many message as possible, or better yet to deduce the key (or keys) used to encrypt the message. In order to decrypt other message encrypted with the same keys.
Types of Cryptanalysis attacks • 2. Known-plaintext attack • The cryptanalyst (attacker) has access not only to the cipher text of several message, but also to the plain text of those message. His job is to deduce the key (or keys) used to encrypt the message or an algorithm to decrypt any new message encrypted with the same key, (or keys).
