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DES (Data Encryption Standard) pressentation

This document discusses data encryption methods. It defines encryption as hiding information so it can only be accessed by those with the key. There are two main types: symmetric encryption uses one key, while asymmetric encryption uses two different but related keys. Encryption works by scrambling data using techniques like transposition, which rearranges the order, and substitution, which replaces parts with other values. The document specifically describes the Data Encryption Standard (DES) algorithm and the public key cryptosystem, which introduced the innovative approach of using different keys for encryption and decryption.

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Data Encryption By khayam Sarhadi Roll No: 130221 BS-CS 7th UOS
 Encryption Definition:  The action of hiding information so that it can be recovered easily by the persons who have the key, but is highly resistant to recovery by persons who do not have the key.
 A message is clear text (plaintext) is encrypted (disguised) through the use of an encryption key to create a Cipher text.
 In symmetric (Single key):  The encryption and decryption keys are the same.  In asymmetric (two keys):  The encryption and decryption keys are different.
 Encryption Methods:  Encryption is skilled by scrambling( ) the bits, characters, words, or phrases in the original message. Scrambling involves two activities:  Transposition ()  Substitution ()
 Transposition:  In which the order of the bits patterns, characters, words or phrases is rearranged.  Substitution:  In which new bit patterns, characters, words, or phrases are substituted for the originals without changing their order.
 Data Encryption Standard (DES):  Most widely used algorithm  Founded by IBM  It is symmetric cryptosystem  Developed to protect sensitive, unclassified, US government, Computer data.  Used to provide authentication of electronic funds transfer messages.
 The basic process in enciphering a  64-bit data block  56-bit key using the DES consists of: • An initial permutation (IP) • 16 rounds of a complex key dependent calculation f • A final permutation, being the inverse of IP
 DES Algorithm:  The algorithm accepts plaintext, P, and performs an initial permutation, IP, on P producing P0, The block is then broken into left and right halves, the Left (L0) being the first 32 bits of P0 and the right (R0) being the last 32 bits of P0.  With L0 and R0, 16 rounds are performed until L16 and R16 are generated.  The inverse permutation, IP-1 , is applied to L16R16 to produce ciphertext C.
 Public Key Cryptosystem  It is an asymmetric cryptosystem.  First announced in 1976.  Offer a radically different approach to encryption.  The idea depends on the use of a pair of keys that differ in a complementary way.  Several algorithms are proposed  RSA algorithm is considered to be highly secure. Tayyab Arif 00923445064252, Allama Iqbal Open University
 Public key encryption can achieved:  Privacy  Authentication