five models of symmetric key algorithm
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19102010, 03:45 PM
Q.docx (Size: 16.32 KB / Downloads: 52) five models of symmetric key algorithm Give a detail Compative study of all five models of symmetric key algorithm? Ans. Secret Key Cryptography With secret key cryptography, a single key is used for both encryption and decryption. the sender uses the key (or some set of rules) to encrypt the plaintext and sends the ciphertext to the receiver. The receiver applies the same key (or ruleset) to decrypt the message and recover the plaintext. Because a single key is used for both functions, secret key cryptography is also called symmetric encryption. Secret key cryptography algorithms Data Encryption Standard (DES) Digital Encryption Standard (DES) is a symmetric block cipher with 64bit block size that uses using a 56bit key. DES encrypts and decrypts data in 64bit blocks, using a 56bit key. It takes a 64bit block of plaintext as input and outputs a 64bit block of ciphertext. Since it always operates on blocks of equal size and it uses both permutations and substitutions in the algorithm. DES has 16 rounds, meaning the main algorithm is repeated 16 times to produce the ciphertext. It has been found that the number of rounds is exponentially proportional to the amount of time required to find a key using a bruteforce attack. So as the number of rounds increases, the security of the algorithm increases exponentially. • Two important variants that strengthen DES are: o TripleDES (3DES): A variant of DES that employs up to three 56bit keys and makes three encryption/decryption passes over the block; 3DES is also described in FIPS 463 and is the recommended replacement to DES. o DESX: A variant devised by Ron Rivest. By combining 64 additional key bits to the plaintext prior to encryption, effectively increases the keylength to 120 bits. Advanced Encryption Standard (AES) In 1997, NIST initiated a very public, 41/2 year process to develop a new secure cryptosystem for U.S. government applications. The result, the Advanced Encryption Standard, became the official successor to DES in December 2001. AES uses an SKC scheme called Rijndael, a block cipher designed by Belgian cryptographers Joan Daemen and Vincent Rijmen. The algorithm can use a variable block length and key length; the latest specification allowed any combination of keys lengths of 128, 192, or 256 bits and blocks of length 128, 192, or 256 bits. NIST initially selected Rijndael in October 2000 and formal adoption as the AES standard came in December 2001. FIPS PUB 197 describes a 128bit block cipher employing a 128, 192, or 256bit key Rijndael is a block cipher, designed by Joan Daemen and Vincent Rijmen as a candidate algorithm for the AES. AES stands for Advanced Encryption Standard. AES is a symmetric key encryption technique which will replace the commonly used Data Encryption Standard (DES). The Advanced Encryption Standard algorithm approved by NIST in December 2001 uses 128bit blocks. The cipher currently supports key lengths of 128, 192, and 256 bits. Each encryption key size causes the algorithm to behave slightly differently, so the increasing key sizes not only offer a larger number of bits with which you can scramble the data, but also increase the complexity of the cipher algorithm. 



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