I'm given a very simple 8 bit block cipher in which to encrypt plaintext x with k k one performs $ x \oplus k $. I am given IV = 0101 and a CTR of value CCCCCCCC (36bits).
My understanding is that counter mode relies on the output block size of my cipher to yield a stream key of b (in this case 8) bits which will then be XORed with my plaintext, and that the bit length of IV and counter should also be b-bits long.
Am I misunderstanding, or did my professor make a mistake with the counter and IV being 40 bits long?
To aide, here is the exact text from the assignment:
Consider a simple system with 8-bit block size. Assume the encryption (and decryption) to be a simple XOR of the key with the input. In other words, to encrypt x with k we simply perform $ x \oplus k $ giving y. Similarly to decrypt y, we perform $ y \oplus k$ giving x.
You are given the following 16-bit input. 1111000011110000 (F0F0 in hex).
You are provided IV as: 00001111 (or 0F in hex).
For CTR assume the stream of bits ot be used for counter to be "110011001100110011001100110011001100" (or CCCCCCCCC)
The key to be used (where appropriate) is 10100011 (A3 in hex).
Compute the encrypted output with (i) ECB, (ii) CBC, (iii) OFB, (iv) CFB, (v) CTR (use IV = 0101 for CTR)