Transmission Security via Fast Time-Frequency Hopping PI: Eli Yablanovich Co-PIs: Rick Wesel Ingrid Verbauwhede Ming Wu Bahram Jalali UCLA Electrical Engineering Department

Four users, each with four bits Alice’s Data: A1, A2, A3, A4 Bob’s Data: B1, B2, B3, B4 Carol’s Data: C1, C2, C3, C4 Dave’s Data: D1, D2, D3, D4

Random Hopping on a Time-Wavelength Grid A user appears on zero, one, or more wavelengths each symbol. Users select positions in grid in an unpredictable fashion. A1 D2 C1 D4 Wavelength 1 A2 C2 C3 B1 Wavelength 2 D1 A4 D3 B2 Wavelength 3 C4 A3 B3 B4 Wavelength 4 Time

Grid-to-Grid Mapping is a Switch 1616 Switch A1 A2 A3 A4 B1 B2 B3 B4 C1 C2 C3 C4 D1 D2 D3 D4 A1 D2 C1 D4 A2 C2 C3 B1 D1 A4 D3 B2 C4 A3 B3 B4 User Wavelength Bit Index Time There are 16! possible configurations of this switch. The switch configuration may be specified by log2(16!)=44.25 bits

Grid-to-Grid Mapping is a Switch 1616 Switch 16 Users (A-P) Wavelength Switch also supports 16 users on 16 wavelengths with wavelength-only hopping at a total rate of 10 Gbps.

A Pipelined Switch There are 16! possible configurations (44.25 bits). Code bit = 0 Code bit = 1 There are 16! possible configurations (44.25 bits). There are 56 switches, but four can be fixed so that 52 bits specify the configuration. Thinking about future feasibility, for a 100100 switch, not all switch positions need to be randomized.

Four Switches Taking Turns 155MHz 2.5Gbps 2.5Gbps 1:16 16X16 Switch 16:1 User 1 Modulator Each 16X16 switch (the blue box) runs at 155 MHz, which is ¼ times 1/16 times 10 GHz. l1 1:16 16X16 Switch 16:1 User 2 Modulator l2 4:1 1:16 16X16 Switch 16:1 User 3 Modulator l3 1:16 16X16 Switch 16:1 User 4 Modulator l4 Pat. Gen 1:16 16:1 Serializer de-Serializer

The Big Picture 1616 Switch Advanced Encryption Standard User Wavelength Bit Index Time We need 52 bits or 9 Gbits/sec (We can do about 20 Gbits/sec) Advanced Encryption Standard Random bit generator (initially just a linear feedback shift register)

What Kinds of Security Are Possible? Security by Obscurity This is no security at all. Obscurity is fleeting. Security by computational difficulty Standardized systems like DES and AES rely on this. Must consider attacks where plain-text is known. The one-time pad that nobody else knows Perfect as long as the pad remains secret.

Hopping versus Spreading Our technique focuses on the addition of cryptographic security in the context of relatively straightforward frequency-hopped CDMA. Certainly, similar techniques could be applied to the other OCDMA techniques described during this meeting. However, in every case, the real security comes from (high speed) cryptographic security rather than obscure optical techniques.

Network Security Most sophisticated security techniques add security at the source only (application layer). Our technique adds security at the physical layer (or at the network layer).

Why Have Network Security? Increase the difficulty of attack, even with plaintext available. (The ciphertext of an individual stream is now difficult to receive.) Adds security with minimal latency (the latency inherent in the timespan of the permutation) because AES processing is not in the real-time path..

Synchronous vs. Asynchronous Our original vision was for a system with 100% spectral efficiency (assuming dense wavelength packing), but with synchronous operation (and a universally known key) as a requirement. However, our system concept can easily trade spectral efficiency to operate asynchronously. In this case each transmitter can have it’s own key. When overhead is low, collisions are rare, and may be handled by a light error correction code. In one scenario 5% spectral efficiency yields a 1% bit error rate.