36 Questions
Which of the following is true about irreducible polynomials?
They cannot be expressed as a product of two polynomials of lower degree
What is the degree of the irreducible polynomial used in AES?
8
How many rounds are there in AES for a 24-byte key?
12 rounds
What is the size of a plaintext block in AES?
128 bits
Which field is used for arithmetic operations in AES?
GF(28)
What is the definition of division in a field?
a/b = a(b-1)
Which set of integers is used for arithmetic defined over a field?
Z2n
What is the definition of a finite field GF(2n)?
A set of all polynomials of degree n with binary coefficients
Which of the following is a stage in the AES encryption process?
Mix columns
What is used in the decryption algorithm to achieve the inverse of the AddRoundKey stage?
XORing the same round key
Which of the following is true about the decryption algorithm in AES?
It uses the expanded key in reverse order
What is the forward transformation called that maps each individual byte of State into a new byte using a table lookup?
Substitute bytes
Which of the following is NOT a stage used in the AES encryption process?
MixColumns
How many rounds are there in the AES encryption process?
10
What is the key size (in bits) for AES encryption with a 256-bit key length?
256
What is the size of the expanded key (in bytes) for AES encryption with a 128-bit key length?
44
Which of the following statements about polynomial arithmetic is true?
The product of polynomials of degrees m and n has degree m + n.
Perform the following polynomial multiplication: $(x^2 + 2x + 9)(x^3 + 11x^2 + x + 7)$.
$x^5 + 13x^4 + 21x^3 + 28x^2 + 9x + 63$
Determine which of the following polynomials are reducible over $GF(2)$:
$x^2 + 1$
Find the greatest common divisor (gcd) of the polynomials $(x^3 + 1)$ and $(x^2 + x + 1)$ over $GF(2)$:
$x^3 + x^2 + x + 1$
According to Equation (6.2), what is the result of the multiplication 1 1 1 1 H 1 0 0 0 4 0 1 1 1 1 1 0 0 0 0 1 1 1 1 1 0 0 0 0 1 1 1 1 1 1 0 0 0 1 1 1 1 1 1 0 0 0 1 1 1 1 1 1 0 0 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 0 0 0 0 1 1 0 1 0 1 XH X ⊕ H X = H X ⊕ H X = H X 0 0 0 0 0 0 0 0 1 0 1 1 0 0 1 1 1 0 1 1 0 0 0 0
{2A}
What is the purpose of the inverse substitute byte transformation, InvSubBytes?
To construct the inverse S-box
Which equation represents the inverse transformation in InvSubBytes?
bi = b(i + 2) mod 8 ⊕ b(i + 5) mod 8 ⊕ b(i + 7) mod 8 ⊕ d
What is the purpose of the inverse S-box in AES?
To perform the inverse substitute byte transformation
What is the input to the inverse S-box that produces the output {2A}?
{2A}
What is the result of the multiplication YX?
The identity matrix
Which of the following is true about the inverse S-box in AES?
The inverse S-box is constructed by applying the inverse of the transformation in Equation (6.1)
Which equation represents the inverse transformation in InvSubBytes?
bi = b(i + 2) mod 8 ⊕ b(i + 5) mod 8 ⊕ b(i + 7) mod 8 ⊕ di
What is the result of the multiplication 1 1 1 1 H 1 0 0 0 4 0 1 1 1 1 1 0 0 0 0 1 1 1 1 1 0 0 0 0 1 1 1 1 1 1 0 0 0 1 1 1 1 1 1 0 0 0 1 1 1 1 1 1 0 0 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 0 0 0 0 1 1 0 1 0 1 XH X ⊕ H X = H X ⊕ H X = H X 0 0 0 0 0 0 0 0 1 0 1 1 0 0 1 1 1 0 1 1 0 0 0 0?
The result is {2A}
What is the input to the inverse S-box that produces the output {2A}?
The input is {95}
What is the purpose of the inverse substitute byte transformation, InvSubBytes?
The purpose is to apply the inverse of the substitute byte transformation
What is the definition of division in a field?
Division in a field is defined as the inverse operation of multiplication
What is the degree of the irreducible polynomial used in AES?
The degree is 8
What is the size of the expanded key (in bytes) for AES encryption with a 128-bit key length?
The size is 176 bytes
What is the forward transformation called that maps each individual byte of State into a new byte using a table lookup?
The forward transformation is called SubBytes
What is the key size (in bits) for AES encryption with a 256-bit key length?
The key size is 256 bits
Test your knowledge of AES S-Boxes with this quiz! Identify the values of y and x for the given table of hexadecimal values. Challenge yourself to recognize the patterns and decrypt the encrypted message.
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