Crypto Study Guide 2

A more efficient implementation can be achieved for a 32-bit processor if operations are defined on _________ words.

32-bit

The AES key expansion algorithm takes as input a four-word (16-byte) key and produces a linear array of __________ words (176 bytes).

44

The standard decryption round has the structure InvShiftRows, InvSubBytes, __________, InvMixColumns.

AddRoundKey

__________ is a block cipher intended to replace DES for commercial applications. It uses a 128-bit block size and a key size of 128, 192, or 256 bits.

Advanced Encryption Standard (AES)

An example of a technique that uses S-boxes that are both random and key dependent is ___________ , which starts with S-boxes filled with pseudorandom digits and then alters the contents using the key.

Blowfish

The input to the encryption algorithm is the XOR of the next 64 bits of plaintext and the preceding 64 bits of ciphertext" is a description of __________ mode

Cipher Black Chaining

Input is processed s bits at a time. Preceding ciphertext is used as input to the encryption algorithm to produce pseudorandom output, which is XORed with plaintext to produce next unit of ciphertext", is a description of the _________ mode of operation.

Cipher Feedback (CFB)

__________ seeks to make the relationship between the statistics of the ciphertext and the value of the encryption key as complex as possible so that even if the attacker can get some handle on the statistics of the ciphertext, the way in which the key was used to produce that ciphertext is so complex it is difficult to deduce the key.

Confusion

Hardware efficiency, software efficiency, preprocessing, random access, provable security, and simplicity are all advantages of __________ mode.

Counter

The __________ block cipher mode of operation is a general purpose block oriented transmission useful for high speed requirements.

Counter (CTR)

The most widely used encryption scheme is based on the __________ adopted in 1977 by the National Bureau of Standards as Federal Information Processing Standard 46.

Data Encryption Standard (DES)

Many block ciphers have a __________ structure which consists of a number of identical rounds of processing and in each round a substitution is performed on one half of the data being processed, followed by a permutation that interchanges the two halves.

Feistel

___________ affects the sequence of bytes in State but does not alter byte contents and does not depend on byte contents to perform its transformation.

InvShiftRows

Operating systems typically provide a built-in mechanism for generating random numbers. For example, __________ uses mouse and keyboard activity, disk I/O operations, and specific interrupts.

Linux

The _________ transformation operates on each column individually. Each byte of a column is mapped into a new value that is a function of all four bytes in that column.

MixColumns

The first N - 1 rounds consist of four distinct transformation functions: SubBytes, ShiftRows, AddRoundKey, and __________ .

MixColumns

__________ is a technique in which an encryption algorithm is used multiple times.

Multiple Encryption

The __________ standard describes a method of encryption for data stored in sector-based devices where the threat model includes possible access to stored data by the adversary. Some characteristics of this standard include: the ciphertext is freely available for an attacker, the data layout is not changed on the storage medium and in transit, and the same plaintext is encrypted to different ciphertexts at different locations.

P1619

__________ algorithms are designed specifically and solely for the purpose of generating pseudorandom bit streams.

Purpose-built

The most important and widely used stream cipher is __________ .

RC4

__________ is a stream cipher designed in 1987 by Ron Rivest for RSA Security.

RC4

The National Institute of Standards and Technology chose the __________ design as the winning candidate for AES.

Rijndael

The forward substitute byte transformation, called _________ , is a simple table lookup.

SubBytes

TRUETrue/False: With true random sequences each number is statistically independent of other numbers in the sequence and therefore unpredictable.

TRUE

True/False: ) Compared to public-key ciphers such as RSA, the structure of AES and most symmetric ciphers is quite complex and cannot be explained as easily as many other cryptographic algorithms.

TRUE

True/False: A mode of operation is a technique for enhancing the effect of a cryptographic algorithm or adapting the algorithm for an application.

TRUE

True/False: A prime concern with DES has been its vulnerability to brute-force attack because of its relatively short key length.

TRUE

True/False: A problem with the ideal block cipher using a small block size is that it is vulnerable to a statistical analysis of the plaintext.

TRUE

True/False: A typical application of Output Feedback mode is stream oriented transmission over noisy channel, such as satellite communication.

TRUE

True/False: A widely used technique for pseudorandom number generation is an algorithm known as the linear congruential method.

TRUE

True/False: AES can be implemented very efficiently on an 8-bit processor.

TRUE

True/False: An advantage of key-dependent S-boxes is that because they are not fixed, it is impossible to analyze the S-boxes ahead of time to look for weaknesses.

TRUE

True/False: At each horizontal point, State is the same for both encryption and decryption.

TRUE

True/False: Cipher Block Chaining is a simple way to satisfy the security deficiencies of ECB.

TRUE

True/False: Fast software encryption/decryption and ease of analysis are two considerations in the design of a Feistel cipher.

TRUE

True/False: Given the potential vulnerability of DES to a brute-force attack, an alternative has been found.

TRUE

True/False: Greater complexity in the subkey generation algorithm should lead to greater difficulty of cryptanalysis.

TRUE

True/False: If the PRF does not generate effectively random 128-bit output values it may be possible for an adversary to narrow the possibilities and successfully use a brute force attack.

TRUE

True/False: 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.

TRUE

True/False: It is possible to convert a block cipher into a stream cipher using cipher feedback, output feedback and counter modes.

TRUE

True/False: OFB mode requires an initialization vector that must be unique to each execution of the encryption operation.

TRUE

True/False: Random numbers play an important role in the use of encryption for various network security applications.

TRUE

True/False: The Feistel cipher structure, based on Shannon's proposal of 1945, dates back over a quarter of a century and is the structure used by many significant symmetric block ciphers currently in use.

TRUE

True/False: The Rijndael developers designed the expansion key algorithm to be resistant to known cryptanalytic attacks.

TRUE

True/False: The S-box is designed to be resistant to known cryptanalytic attacks.

TRUE

True/False: The XTS-AES mode is based on the concept of a tweakable block cipher.

TRUE

True/False: The heart of a Feistel block cipher is the function F, which relies on the use of S-boxes.

TRUE

True/False: The inverse add round key transformation is identical to the forward add round key transformation because the XOR operation is its own inverse.

TRUE

True/False: The longer the keyword the more difficult the cryptanalysis.

TRUE

True/False: The nonlinearity of the S-box is due to the use of the multiplicative inverse.

TRUE

True/False: The ordering of bytes within a matrix is by column.

TRUE

True/False: The principle requirement of random or pseudorandom number generation is that the generated number stream be unpredictable.

TRUE

True/False: The security of Blum, Blum, Shub is based on the difficulty of factoring n.

TRUE

True/False: The seed that serves as input to the PRNG must be secure for cryptographic applications.

TRUE

True/False: The true random number generator may simply involve conversion of an analog source to a binary output.

TRUE

True/False: There are no practical cryptanalytic attacks on 3DES.

TRUE

True/False: Three broad categories of cryptographic algorithms are commonly used to create PRNGs: symmetric block ciphers, asymmetric ciphers, and hash functions and message authentication codes.

TRUE

True/False: Virtually all encryption algorithms, both conventional and public-key, involve arithmetic operations on integers.

TRUE

A change in one bit of the plaintext or one bit of the key should produce a change in many bits of the ciphertext. This is referred to as the __________ effect.

avalanche

The __________ criterion is defined as: "An S-box satisfies GA of order y if, for a 1-bit input change, at least y output bits change."

avalanche (GA)

A stream of pseudorandom numbers should exhibit two forms of unpredictability: forward and __________ .

backward

The __________ criterion states that output bits j and k should change independently when any single input bit i is inverted for all i, j and k.

bit independence

A _________ is an encryption/decryption scheme in which a block of plaintext is treated as a whole and used to produce a ciphertext block of equal length.

block cipher

The four separate functions of the Advanced Encryption Standard are: permutation, arithmetic operations over a finite field, XOR with a key, and __________

byte substitution

The plaintext of a sector or data unit is organized in to blocks of 128 bits. For encryption and decryption, each block is treated independently. The only exception occurs when the last block has less than 128 bits. In that case the last two blocks are encrypted/decrypted using a ___________ technique instead of padding.

ciphertext-stealing

The requirements for encrypting stored data, also referred to as ___________ , differ somewhat from those for transmitted data.

data at rest

The rationale behind __________ cryptanalysis is to observe the behavior of pairs of text blocks evolving along each round of the cipher instead of observing the evolution of a single text block.

differential

In ___________ the statistical structure of the plaintext is dissipated into long-range statistics of the ciphertext. This is achieved by having each plaintext digit affect the value of many ciphertext digits.

diffusion

The simplest mode of operation is the ___________ mode, in which plaintext is handled one block at a time and each block of plaintext is encrypted using the same key.

electronic codebook

The most significant characteristic of __________ is that if the same b-bit block of plaintext appears more than once in the message, it always produces the same ciphertext.

electronic codebook mode (ECB)

The __________ is drawn from the physical environment of the computer and could include things such as keystroke timing patterns, disk electrical activity, mouse movements, and instantaneous values of the system clock.

entropy source

wo criteria used to validate that a sequence of numbers is random are uniform distribution and __________ .

independence

A polynomial m(x) is called __________ if and only if m(x) cannot be expressed as a product of two polynomials, both of degree lower than that of m(x).

irreducible

The cipher consists of N rounds, where the number of rounds depends on the __________

key length

Two areas of concern regarding the level of security provided by DES are the nature of the algorithm and the __________

key size

In a stream cipher structure a key is input to a pseudorandom bit generator that produces a stream of 8-bit numbers that are apparently random. The output of the generator, called a ___________ , is combined one byte at a time with the plaintext stream using the bitwise exclusive-OR operation.

keystream

Two important methods of cryptanalysis are differential cryptanalysis and _________ cryptanalysis. 19) _____________

linear

A __________ is a technique for enhancing the effect of a cryptographic algorithm or adapting the algorithm for an application, such as applying a block cipher to a sequence of data blocks or a data stream.

mode of operation

The _________ must be a data block that is unique to each execution of the encryption operation and may be a counter, a timestamp, or a message number.

nonce

Five modes of operation have been standardized by NIST for use with symmetric block ciphers such as DES and AES: electronic codebook mode, cipher block chaining mode, cipher feedback mode, __________, and counter mode.

output feedback mode (OFB)

A fundamental requirement of the RSA public-key encryption scheme is the ability to generate _________ numbers.

prime

An example of a finite field is the set Zp consisting of all the integers {0, 1, . . . , p - 1}, where p is a __________ and in which arithmetic is carried out modulo p.

prime number

If the algorithm is good the resulting sequences will pass many reasonable tests of randomness. These numbers are referred to as ___________ numbers.

pseudorandom

Typically the __________ takes as input a seed plus some context specific values such as a user ID or an application ID.

pseudorandom function (PRF)

An algorithm that is used to produce an open-ended sequence of bits is referred to as a ___________ .

pseudorandom number generator (PRNG)

Two distinct requirements for a sequence of random numbers are unpredictability and __________ .

randomness

The purpose of the __________ test is to determine whether the number of runs of ones and zeros of various lengths is as expected for a random sequence.

runs

The mix column transformation combined with the __________ transformation ensures that after a few rounds all output bits depend on all input bits.

shift row

A __________ cipher can operate in real time and eliminates the need to pad a message to be an integral number of blocks.

stream

A __________ is a symmetric encryption algorithm in which ciphertext output is produced bit-by-bit or byte-by-byte from a stream of plaintext input.

stream cipher

The __________ criterion states that any output bit j of an S-box should change with probability 1/2 when any single input bit i is inverted for all i,j.

strict avalanche

AES processes the entire data block as a single matrix during each round using __________ and permutation.

substitutions

The cryptographic strength of a Feistel cipher derives from three aspects of the design: the function F, the key schedule algorithm, and __________

the number of rounds

A _________ attack exploits the fact that an encryption or decryption algorithm often takes slightly different amounts of time on different inputs.

timing

One of the most widely used multiple-encryption scheme is __________ .

triple DES