Speed of Decision Making

The Bernoulli trial XOR formulation of the decision problem allows us to exploit the 32-bit architecture of a CPU for 16-fold parallelization. Since iris code comparisons are fully vectorizable bitwise, they can be implemented in parallel in single-cycle logic at the register level using 16-bit integer XOR. As a result, on a RISC general-purpose CPU any ``presenting" iris code can be compared exhaustively against a large database of stored codes in search of a match at the rate of about 4,000 per second. (This clocked rate includes significant overhead due to complete iris code transfers, as well as table look-up to convert 16-bit integer XOR outcomes into running sums of Hamming distance.) With dedicated hardware, fuller vectorization can be achieved and a further 40,000-fold speed-up in recognition is now possible. Since the decision process, including the calculation of confidence levels, relies only on computing the logical XOR vector between two iris codes comprising 2,048 bits, conventional SSI devices that have been available for decades at negligible cost offer the basis for immediate parallel implementation. For example, the simple 74F86 integrated circuit contains four independent XOR gates that can be clocked at 80 megahertz. Thus a 32 x 32 array of 74F86 ICs (or a single equivalent dedicated gate array) could in principle execute comparisons and decisions at the rate of 160 million complete iris codes per second, if exhaustive database searches were required and if such databases existed.

Because of the speed of decision-making made possible by the commensurability of iris codes, it is not even necessary in this method for a Subject to make any claims about his identity (e.g. by entering a password, PIN, or swiping a card) that the biometric comparison then merely confirms or disconfirms. Rather, here he only needs to present his eye to the camera, and his identity is rapidly and automatically determined without any further interaction, by exhaustive search through a database that might be extremely large. As Shakespeare conveyed it much less mechanically in The Merchant of Venice (Act I, Scene 1), in the tradition of conceiving the eyes as windows to the soul, ``Sometimes from her eyes I did receive fair speechless messages."