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Symmetric Encryption Assignment

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Added on  2020-10-09

Symmetric Encryption Assignment

   Added on 2020-10-09

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Week 2 Lecture 1 - Cryptography 21Week 2 Lecture 1 - Cryptography 2Symmetric EncryptionIf the encryption and decryption keys are the same, then That is, the decryption, via the key, of the encryption, via the key, of the plaintext is the plaintext. This is known as Symmetric Encryption.Converting the ciphertext back into the plaintext requires a separate process.Symmetric algorithms use one key, a secret key encryption but for an N-user system, we would require n(n-1)/2 keys for each pair of users.Asymmetric EncryptionAsymmetric Encryption implies the keys are in complementary pairs. A decryption key, , inverts the encryption key .In public key or asymmetric encryption, each user has two keys: a public and a private key. The public key is published freely because it is only one half of an inverse pair.The public key encryption is decrypted via the private key.The private key encryption is decrypted via the public key. Multiple users can send messages privately to each other using public keys.Diffie-Hellman Key ExchangeDiffie and Hellman published the first paper on public key cryptography where a sender and receiver use simple arithmetic to exchange keys.There are three conditions:It must be computationally easy to encode/decode with a key.P = D(K, E(K, P ))KDKEP = D(K , E(K , P ))DEP = D(K, E(K, P ))privatepublicP = D(K, E(K, P ))publicprivate
Symmetric Encryption Assignment_1
Week 2 Lecture 1 - Cryptography 22It must be computationally infeasible to derive the private key from the public key.It must be computationally infeasible to determine the private key from a plaintext attackMathematically we require to find k such that Where p is prime and g 0,1 or p-1, g and p are agreed a priori.RSAThe RSA cryptosystem is a public-key system that has been a de-facto standard for many years.where and are prime numbers. The totient (n) is the number of numbers less than n with no factors in common with () and ().Commercial NeedsWhen an encryption has to be of a commercial grade, i.e. trustworthy, has to be based on sound mathematics, be analysed and tested.Three algorithms have been used in the business world:DESAESRSAStream and Block CiphersStream ciphers convert one plaintext character at a time while a block cipher encyrpts a group of characters at a time and treats this as a single block entity. Stream ciphers have low error propagation, because only one character is encoded at a time, but they can be susceptible to malicious insertions or modifications. They are fast to encrypt.Block ciphers are highly diffused, information about a character (or the plaintext) is spread out in th eciphertext. Errors may be propogated within the block and encryption is slower. Padding of blocks occurs.n = g mod pkn = pqpqp − 1q − 1
Symmetric Encryption Assignment_2

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