Crypto CH 5

In AES, the arithmetic operations of addition, multiplication and division are performed over the finite field _________ . A)GF(2^8) B)GF(2^n-1) C)Zp D)a/b = a(b-1)

A) GF(2^8)

The cipher consists of N rounds, where the number of rounds depends on the A)key length B)State C)output matrix D)number of columns

A) Key Length

In the general structure of the AES encryption process the input to the encryption and decryption algorithms is a single _________ block. A)128 - bit B)256 - bit C)64 - bit D)32-bit

A)128 - bit

__________ affects the contents of bytes in State but does not alter byte sequence and does not depend on byte sequence to perform its transformation A)InvSubBytes B)InvShiftRows C)ShiftRows D)SubBytes

A)InvSubBytes

A __________ is a set in which you can do addition, subtraction, multiplication and division without leaving the set. A)block B)field C)standard D)record

B)Field

The __________ is when a small change in plaintext or key produces a large change in the ciphertext. A)auxiliary exchange B)avalanche effect C)Rcon D)key expansion

B)avalanche effect

Division requires that each nonzero element have a(n) __________ inverse. A)subtraction B)divisional C)multiplicative D)addition

B)multiplicative

In the AES structure both encryption and decryption ciphers begin with a(n) __________ stage, followed by nine rounds that each include all four stages, followed by a tenth round of three stages. A)ShiftRows B)Substitute bytes C)AddRoundKey D)MixColumns

C) AddRoundKey

The final round of both encryption and decryption of the AES structure consists of __________ stages. A)four B)one C)three D)two

C) Three

The first row of State is not altered; for the second row a 1-byte circular left shift is performed; for the third row a 2-byte circular left shift is performed; and for the fourth row a 3-byte circular left shift is performed. This transformation is called A)AddRoundKey B)Substitute bytes C)ShiftRows D)MixColumns

C)ShiftRows

In the AddRoundKey transformation the 128 bits of State are bitwise XORed with the _________ of the round key. A)256 bits B)512 bits C)64 bits D)128 bits

D) 128 Bits

The AES cipher begins and ends with a(n) _________ stage because any other stage, applied at the beginning or end, is reversible without knowledge of the key and would add no security. A)Substitute bytes B)MixColumns C)ShiftRows D)AddRoundKey

D) AddRoundKey

The Advanced Encryption Standard was published by the __________ in 2001. A)FIPS B)IEEE C)ARK D)NIST

D)NIST

AES uses a Feistel structure

False

As with any block cipher, AES can be used to construct a message authentication code, and for this, only decryption is used.

False

DES is a block cipher intended to replace AES for commercial applications.

False

In the Advanced Encryption Standard the decryption algorithm is identical to the encryption algorithm.

False

InvSubBytes is the inverse of ShiftRows.

False

The transformations AddRoundKey and InvMixColumn alter the sequence of bytes in State.

False

At each horizontal point, State is the same for both encryption and decryption.

True

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

The Rijndael developers designed the expansion key algorithm to be resistant to known cryptanalytic attacks.

True

The S-box is designed to be resistant to known cryptanalytic attacks.

True

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

True

The nonlinearity of the S-box is due to the use of the multiplicative inverse.

True

The ordering of bytes within a matrix is by column.

True

In Advanced Encryption Standard all operations are performed on __________ bytes. A)16-bit B)8-bit C)32-bit D)4-bit

B)8-Bit

The encryption round has the structure: A)ShiftRows, MixColumns, SubBytes, InvMixColumns B)InvShiftRows, InvSubBytes, AddRoundKey, InvMixColumns C)SubBytes, ShiftRows, MixColumns, AddRoundKey D)MixColumns, ShiftRows, SubBytes, AddRoundKey

C)SubBytes,ShiftRows,MixColumns,Rows,AddRoundKey

AES can be implemented very efficiently on an 8-bit processor.

True

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

True