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

Wavelength 1 Wavelength 2 Wavelength 3 Wavelength 4 A1D2C1D4 A2C2C3B1 D1A4D3B2 C4A3B3B4 Time 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.

Grid-to-Grid Mapping is a Switch 16  16 Switch There are 16! possible configurations of this switch. The switch configuration may be specified by log 2 (16!)=44.25 bits A1A2A3A4 B1B2B3B4 C1C2C3C4 D1D2D3D4 Bit Index Time User Wavelength A1D2C1D4 A2C2C3B1 D1A4D3B2 C4A3B3B4

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

A Pipelined Switch 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. Code bit = 0 Code bit = 1

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

The Big Picture Advanced Encryption Standard Random bit generator (initially just a linear feedback shift register) We need 52 bits or 9 Gbits/sec (We can do about 20 Gbits/sec) 16  16 Switch A1A2A3A4 B1B2B3B4 C1C2C3C4 D1D2D3D4 Bit Index Time User Wavelength A1D2C1D4 A2C2C3B1 D1A4D3B2 C4A3B3B4

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 that is easily handled with error correction.

Improving Multicast Throughput with Network Coding Consider a Multicast of b1 and b2 from S to R1 & R2.. Conventional “ Replicate & Forward ” Routing needs at least 2 transmission times. Linear Combination of Data at intermediate Nodes requires only one transmission time. b1b2 b1 B1` + b2 b1 + b2 R1R2 S