plaintextciphertext encryption algorithmdecryption algorithm plaintext

Round 1 Round 2 Round N XYWJLRAM block of ciphertext Horst Feistel (IBM) invented the basic algorithm in Feistel ciphers use symmetric block encryption relying upon product transformations. HI Mom S block of plaintextKey f + f + f + subkey 1 subkey 2 subkey N f some function + exclusive OR (bitwise) Encryption & decryption use the same algorithm.

DES Data Encryption Standard - an algorithm selected by the National Institute of Standards Technology for the encryption of non-classified data. The current DES algorithm was adopted by the U.S. Nat. Bureau of Standards in Block size: ____ bits Key size: ____ bits + 8-bit parity 16-round Feistel encryption (preceded by one permutation and followed by the permutation ’ s inverse) Subkeys The key (56-bits) is split in two and each half is rotated left by 1 or 2 bits. The resulting two 28-bit values index into a table to produce a 48-bit subkey. The rotated values are also forwarded to compute the next subkey. f function 1) input to f is expanded from 32 to 48 bits via table lookup 2) 48-bit value from (1) is XORed with subkey 3) 48-bit value from (2) is partitioned into eight 6-bit values 4) 6-bit values from (3) are separated into outside 2 bits and center 4 bits (outside bits select row and inside bits select column from S-box table) 5) eight S-box lookup values (each 4 bits long) are concatenated

The DES cipher substitutes via eight different S-boxes; two are below.

Brute Force brute force attacks might be possible in the future [Diffie & Hellman IEEE Computer, June] Time to Produce All Possible Encodings Key Size (in bits) Number of Keys(1 encrypt./  s) (10 6 encrypt./  s) ≈ 4.3 X min. 2 msec ≈ 7.2 X years 10 hr ≈ 3.4 X X years 5.4 X years 26-char permutation 26! ≈ 4 X X years 6.4 X 10 6 years a distributed collection of 3500 research computers discover DES key in ___ months Electronic Frontier Foundation builds ___________________________________. REF: Net uses DES Cracker plus 100,000 PCs to crack DES in under ______________.

______ also called triple DES use two keys and three DES encryptions cipher = E key1 ( D key2 ( E key1 ( plaintext ) ) ) 3DES has an effective key size of 112 bits. developed by Bruce Schneier compact, efficient, algorithm w/ key of 128 bits International Data Encryption Algorithm developers from Swiss Federal Institute of Technology 128-bit key, but differs from DES in round function and subkey generation. ______ ___________ Advanced Encryption Standard selected algorithm: Rijndael a product cipher using key sizes of 128, 192 and 256 bits (128-bit block size). ______ developed by Ron Rivest efficient algorithm with variable length keys ______

Advantages only one key to generate relatively well-tested and established algorithms cipher algorithms are efficient potentially large number of keys Disadvantages ______________________________ (How can this be accomplished securely?) number of private keys number of communicators23456n