The modern stream and block ciphers used today are sophisticated encryption algorithms that run on high-speed computers,but their origins were in simple physical devices used during colonial times. An example of such an early device is the cipher disk. The cipher disk was actually composed of two disks, each with the alphabet inscribed around its edge.Since the diameter of the disks varied, the manner in which the alphabets lined up differed from set to set. To further complicate the matter, an offset, or staring point, was chosen. Only the possessor of a duplicate disk set with knowledge of the offset could produce the same "stream" of characters.