1. UCLA Electrical Engineering Department
Techniques for Transmission Security via Fast Hopping in the Time-Frequency Grid
PI’s:
Eli Yablanovich
Rick Wesel
Ingrid Verbauwhede
Ming Wu
Bahram Jalali
UCLA Electrical Engineering Department

2. 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.

3. Physical Layer Security
Most sophisticated security techniques add security at the source only (application layer).
Our technique adds security at the physical layer.

4. Why Have Physical Layer 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).
Significantly enhances archival security.

5. 1 2 3 4 The User-Message Grid User Symbol Time Diagonal Dappled
Bricked
Checked
Symbol Time

6. Time-Wavelength Grid (WDM)

7. Periodic Wavelength Hopping
Each user appears on exactly one wavelength each symbol time.
Users cycle through wavelengths in a predictable fashion. 1 2 3 4
Wavelength 1 1 2 3 4
Wavelength 2 1 2 3 4
Wavelength 3 1 2 3 4
Wavelength 4
Time

8. Random Wavelength Hopping
Each user appears on exactly one wavelength each symbol time.
Users select wavelengths in an unpredictable fashion. 1 2 3 4
Wavelength 1 1 2 3 4
Wavelength 2 1 2 3 4
Wavelength 3 1 2 3 4
Wavelength 4
Time

9. 4 1 2 1 2 2 3 1 1 4 3 2 4 3 3 4 Random Grid Hopping Time Wavelength 1
A user appears on zero, one, or more wavelength each symbol.
Users select positions in grid in an unpredictable fashion. 1 2 1 4
Wavelength 1 2 2 3 1
Wavelength 2 1 4 3 2
Wavelength 3 4 3 3 4
Wavelength 4
Time

10. Advantage of Random Hopping on the Grid
Even if an eavesdropper can tell which elements of the grid are being used by a transmitter, the eavesdropper still does know how to permute the bits to understand the data.

11. Grid-to-Grid (G2G) Mapping
1616
Switch 1 2 4 3 1 2 3 4

12. Grid-to-Grid Mapping is a Switch
1616
Switch 1 2 4 3 1 2 3 4
There are 16! possible configurations of this switch.
The switch configuration may be specified by log2(16!)=44.25 bits.

13. 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 bits used to specify the configuration.
Several bit patterns specify the same configuration.

14. Security of Grid-to-Grid Mapping
This mapping needs to be cryptographically secure.
Pseudo-random sequences (Maximal-length sequences) are not secure.
A time-fixed mapping is not secure.
We’ll ultimately use DES/AES encryption technology to produce G2G mappings from “cryptographically-secure” random sequences.
Our first demo will use a linear feedback shift register for simplicity.

15. 4 1 2 3 1 2 3 4 The Big Picture Advanced Encryption Standard
56 bits
(9 Gbits/sec)
Advanced Encryption Standard
Random bit generator
(initially just a linear feedback shift register)

16. Fast-enough AES implementation
Design
# 1
# 2
# 3
# 4
# 5
Clock per Sample 1 4 5
Pipe stages per round
stages
stages
Total pipe stages
4  10 stages
3  10 stages
Latency
4  10 cycles
4  3  10 cycles
5  3  10 cycles
(4  10) + 4 cycles
FPGA Throughput
(200MHz)
Gbit/s
Gbit/s
ASIC Critical path
1.5 ns
650 MHz
1 ns
1 GHz
Estimated Area
Less than 500 Kgates
Less than 900 Kgates
Less than 150 Kgates
Less than 300 Kgates
Less than 250 Kgates
ASIC Throughput
(128*650)
83.2 Gbit/s
(128*1)
128 Gbit/s
(128*650/4) 20.8 Gbit/s
(128*1/5) 25.6 Gbit/s
(128*1/4)
32 Gbit/s

17. Ping-Ponging Switches
155MHz
2.5Gbps
2.5Gbps
1:16
16X16
Switch
16:1
User 1
Modulator l1
1:16
16X16
Switch
16:1
User 2
Modulator l2
16X16
Switch
4:1
1:16
16:1
User 3
Modulator l3
16X16
Switch
1:16
16:1
User 4
Modulator l4
Pat. Gen
Serializer
1:16
16:1
de-Serializer

18. Summary
The random mapping changes with every grid through a high-rate random sequence of bits (common to transmitter and receiver).
The two main non-optical implementation issues are
a fast switch (accomplished through pipelining and ping-ponging)
a fast AES implementation.