GIAC
GSEC · Question #286
GSEC Question #286: Real Exam Question with Answer & Explanation
The correct answer is D. Shift Rows. The ShiftRows transformation in AES performs a cyclic left shift on each row of the 4x4 state matrix by a row-dependent offset.
Question
Which of the four basic transformations in the AES algorithm involves the leftward circular movement of state data?
Options
- ASubBytes
- BMixColumns
- CAddRoundKey
- DShift Rows
Explanation
The ShiftRows transformation in AES performs a cyclic left shift on each row of the 4x4 state matrix by a row-dependent offset.
Common mistakes.
- A. SubBytes is a non-linear substitution step that replaces each byte in the state using the AES S-box lookup table, with no shifting involved.
- B. MixColumns treats each column as a polynomial and multiplies it by a fixed matrix over GF(2^8), producing column-level diffusion rather than any shifting.
- C. AddRoundKey XORs the current state with a portion of the expanded key schedule and performs no movement or permutation of state bytes.
Concept tested. AES ShiftRows transformation mechanics
Reference. https://csrc.nist.gov/publications/detail/fips/197/final
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