Question

Consider a k=8 block cipher.

a. How many input blocks can there be?

A. 8
B 6
C. 64
D. 256
b. How many different arrangements?
A. 8
B. 16
C. 64
D. 256
c. If we consider each arrangement as a key, how many keys are there for the above encryption method?
A. 8
B. 16
C. 64
D. 256

Answer 1

For a k=8 block cipher, there are 256 possible input blocks, 256 different arrangements, and consequently, 256 possible keys if each arrangement is considered a separate key.

Step-by-step explanation:

Regarding a k=8 block cipher:

1. Number of input blocks: The number of possible input blocks is based on the size of the block. Since each block is 8 bits, there are 2^8 possible combinations, which gives us 256 potential input blocks. Therefore, the answer is D. 256.
2. Different arrangements: If we understand different arrangements to refer to the number of possible permutations of the 8-bit block, since each bit has 2 possibilities (0 or 1), we again have 2^8 possible arrangements, equating to 256. Hence, the answer here is also D. 256.
3. Number of keys: If each arrangement is considered a key, then the number of keys is equal to the number of different arrangements. So there are 256 possible keys, making the answer D. 256.

It's important to note that these numbers represent the theoretical maximum based on the block size and do not take into account practical constraints such as key management or security considerations. In real-world applications, not all possible key combinations may be used.