Data Encryption Standard
CS-471/971
• Category of Standard: Computer Security.
• Explanation: The Data Encryption
Standard (DES) specifies a FIPS approved
cryptographic algorithm as required by
FIPS 140-1.
• Qualifications. The cryptographic
algorithm specified in this standard
transforms a 64-bit binary value into a
unique 64-bit binary value based on a 56-bit
variable.
• As there are over 70,000,000,000,000,000
(seventy quadrillion) possible keys of 56
bits, the feasibility of deriving a particular
key in this way is extremely unlikely in
typical threat environments.
• The algorithm is designed to encipher and
decipher blocks of data consisting of 64 bits
under control of a 64-bit key
• A block to be enciphered is subjected to an
initial permutation IP and then to a
complex key-dependent computation and
finally to a permutation which is the inverse
of the initial permutation IP
-1
.
Introduction
• Permutation is an operation performed by
a function, which moves an element at place
j to the place k.
• The key-dependent computation can be
simply defined in terms of a function f,
called the cipher function, and a function
KS, called the key schedule .
• First, a description of the computation.
