Techniques for Transmission Security via Fast Hopping in the Time-Frequency Grid

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Techniques for Transmission Security via Fast
Hopping in the Time-Frequency Grid

• PIs
• Eli Yablanovich
• Rick Wesel
• Ingrid Verbauwhede
• Ming Wu
• Bahram Jalali

UCLA Electrical Engineering Department
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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.

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Physical Layer Security

• Most sophisticated security techniques add
  security at the source only (application layer).
• Our technique adds security at the physical layer.

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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.

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The User-Message Grid
User
Diagonal
Dappled
Bricked
Checked
Symbol Time
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Time-Wavelength Grid (WDM)
Wavelength 1
Wavelength 2
Wavelength 3
Wavelength 4
Time
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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
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Random Wavelength Hopping

• Each user appears on exactly one wavelength
  each symbol time.
• Users cycle through wavelengths in a
  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
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Random Grid Hopping

• 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
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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.

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Grid-to-Grid (G2G) Mapping
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Grid-to-Grid Mapping is a Switch

• There are 16! possible configurations of this
  switch.
• The switch configuration may be specified by
  log2(16!)44.25 bits.

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A Pipelined Switch

• There are 16! possible configurations (44.25
  bits).
• There are 56 bits used to specify the
  configuration.
• Several bit patterns specify the same
  configuration.

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Ping-Ponging Switches
Each 16X16 switch (green box) runs 155 MHz which
is ¼ the rate of 1/16 times 10 GHz.
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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.
• Well 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.

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The Big Picture
56 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)
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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.