DES uses a 56-bit block and a 64-bit key.

If the bit-stream generator is a key-controlled algorithm the two

users only need to share the generating key and then each can

produce the keystream.

A problem with the ideal block cipher using a small block size is

that it is vulnerable to a statistical analysis of the plaintext.

Confusion seeks to make the statistical relationship between the

plaintext and ciphertext as complex as possible in order to thwart

attempts to deduce the key.

All other things being equal, smaller block sizes mean greater

security.

Greater complexity in the subkey generation algorithm should lead

to greater difficulty of cryptanalysis.

Fast software encryption/decryption and ease of analysis are two

considerations in the design of a Feistel cipher.

A sequence of plaintext elements is replaced by a __________ of that sequence

which means that no elements are added, deleted or replaced in the

sequence, but rather the order in which the elements appear in the sequence

is changed.

A __________ cipher is one that encrypts a digital data stream one bit or one

byte at a time.

The vast majority of network-based symmetric cryptographic applications

make use of ________ ciphers.

A __________ cipher is one in which a block of plaintext is treated as a whole

and used to produce a ciphertext block of equal length.

__________ is when each plaintext element or group of elements is uniquely

replaced by a corresponding ciphertext element or group of elements.

Key sizes of __________ or less are now considered to be inadequate.

Feistel proposed that we can approximate the ideal block cipher by utilizing

the concept of a __________ cipher, which is the execution of two or more

simple ciphers in sequence in such a way that the final result or product is

cryptographically stronger than any of the component ciphers.

The criteria used in the design of the __________ focused on the design of the

S-boxes and on the P function that takes the output of the S-boxes.

The greater the number of rounds, the __________ it is to perform cryptanalysis.

A prime concern with DES has been its vulnerability to brute-force

attack because of its relatively short key length.

The heart of a Feistel block cipher is the function F, which relies

on the use of S-boxes.

The function F provides the element of __________ in a Feistel cipher.

One of the most intense areas of research in the field of symmetric block

ciphers is __________ design.

Mister and Adams proposed that all linear combinations of S-box columns

should be _________ which are a special class of Boolean functions that are

highly nonlinear according to certain mathematical criteria.

The Nyberg approach that is more or less a manual approach with only

simple mathematics to support it is __________ .

Allowing for the maximum number of possible encryption mappings from the

plaintext block is referred to by Feistel as the __________ .

DES exhibits the classic __________ block cipher structure, which consists of a

number of identical rounds of processing.