The right-hand half of the next cipher, Ri+1, however, is a complex function of the key and of the entire preceding intermediate cipher. Ri is transposed to become the left-hand part of the next higher intermediate cipher, Li+1. At each intermediate stage of the transformation process, the cipher output from the preceding stage is partitioned into the 32 leftmost bits, Li, and the 32 rightmost bits, Ri. The cipher function (substitution and transposition) that is used with the key bits in each round is labeled f. Subsets of the key bits are designated K1, K2, etc., with the subscript indicating the number of the round. The actual key length is therefore 56 bits. Only 56 of these, however, are at the user's disposal the remaining eight bits are employed for checking parity. The key, which controls the transformation, also consists of 64 bits. The block size is 64 bits, so that a 64-bit block of data (plaintext) can be encrypted into a 64-bit ciphertext. The US National Institute of Standards and Technology with help from the National Security Agency took IBM's design and made some changes DES was adopted as a standard in January 1977.ĭES is a product block encryption algorithm (a cipher) in which 16 iterations, or rounds, of the substitution and transposition (permutation) process are cascaded. It was developed by IBM under the name Lucifer, and was submitted to NBS in response to a 1973 solicitation for better cryptosystems. The Data Encryption Standard (DES) was a widely-used algorithm for encrypting data.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |