# Returns a rearranged format of the ciphertext where every byte of a slot will be XORed with the same offset of a key of length `keylength`.
	private fun transpose_ciphertext(keylength: Int): Array[Bytes] do
		var transposed = new Array[Bytes]
		for i in [0 .. keylength[ do
			transposed.add(new Bytes.empty)
		end

		for byte_idx in [0 .. ciphertext.length[ do
			transposed[byte_idx % keylength].add(ciphertext[byte_idx])
		end

		return transposed
	end