This document discusses security issues in fiber optic networks and various encryption techniques used to secure communication over these networks. It first provides background on optical fibers and fiber optic communication systems. It then outlines some common security issues like network attacks that disrupt service or allow tapping of data. Various encryption schemes are discussed like optical CDMA, quantum cryptography, chaos-based encryption, and steganography. Each technique has advantages but also limitations in terms of things like synchronization requirements, vulnerability to jamming, or limited transmission range.

1. Secure Communication Over
Fiber Optic Networks
Fiona Rozario
D Y Patil School of Engg. & Technology
M.E. (CN) – I
22nd March, 2016

2. Contents
 Optical Fiber Networks
 What are optical fibers?
 Working principle of optical fibers
 Types of optical fibers
 Fiber optic communication system
 Advantages of using fiber optics in communication
 Security issues in fiber optic networks
 Encryption systems
 What is encryption?
 Encryption schemes
 Optical cryptography
 Steganography

3. What are optical fibers?
 A flexible, transparent fiber made of
glass or plastic
 Slightly thicker than human hair
 Its function is to guide visible and
infrared light over long distances

4. What are optical fibers?

5. Working principle of optic fibers
Total internal reflection

6. Fiber optic communication system

7. Advantages of fiber optics in communication
networks
• Longer life than copper wire
• Nominal handling and installation costs
• Unaffected by electromagnetic interference
• Attenuation much lower than coaxial cable or twisted pair
(about 0.2dB/km)
• No issue of protecting against grounding and voltage
problems
• Higher BW offered

8. Security Issues
 Network attacks can be classified as:
 Service disruptions: prevents communication or degrades QoS
 Tapping: unauthorized access to data, compromises privacy
 Physical layer attacks
 Direct attacks: characteristics of physical elements changed
 Indirect attacks: introducing crosstalk

9. Security Issues
Attacks aimed at:
 Network transmission – tapping, jamming

10. Security Issues – Direct attacks
Attacks aimed at:
 Optical amplifiers – jamming

11. Security Issues – Direct attacks
Attacks aimed at:
 Optical cross-connects – in-band and out-of-band crosstalk

12. Security in optical networks
Security –
 Physical security – ensures minimum privacy of data and
QoS
 Semantic security – protects meaning of the data even if it
has already been reached by the attacker
Deals with cryptopraphy

13. What is encryption?
 Mathematical altering data (plaintext) in a
consistent manner to form a unintelligible ciphertext
 Reversible process
 Relies on a secret key

14. Encryption schemes
Building blocks of all cipher algorithms:
• Substitution – replace bits/characters/blocks of
data with substitutes
• Transposition - rearrange replace
bits/characters/blocks of data

15. Encryption schemes

16. Optical encryption schemes
 Optical CDMA
 Quantum cryptography
 Chaos based encryptions
 Steganography

17. Optical CDMA
• An optical short pulse is spread over a one-bit duration T by encoding.
• The decoding time despreads the signal, reconstructing the signal if the codes
between the encoder and decoder match.
• The signal remains spread over T if the codes do not match.

18. Coherent OCDMA

19. Incoherent OCDMA

20. Elements of Quantum Cryptography
 Light waves are propagated as discrete quanta called photons.
 They are massless and have energy, momentum and angular
momentum called spin.
 Spin carries the polarization – plane in which the electric field
oscillates.
 Photons of different polarizations represent the different
quantum states
 Polarization basis is the mapping we decide to use for a
particular state

21. Quantum Cryptography
 Deals with secure key distribution
 Key transmitted at a lower rate than data but at a
higher security level
 Key information is coded onto the quantum states of
a photon

22. Chaos based encryption
 Masks the confidential data with stronger chaos
 Enhances robustness of data transmission

23. Steganography
Aim –
to hide the signal in the existing public channels; hacker should be unable
to detect the presence of a signal

24. Steganography
Approach 1 -
 temporally stretch a short optical pulse through chromatic
dispersion
 Without the correct dispersion compensation at the receiver,
signal stays buried in the noise of the public channel
 Attacker can use tunable dispersion compensating device to check
presence of stealth signals
 Fine tune the device to retrieve the stealth signal

25. Steganography
Approach 2 –
Add temporal phase masks

26. Steganography
Approach 3 -
 Employ ASE noise from amplifiers
 ASE noise from EDFA is most prevalent in optic systems
 ASE noise carrying stealth signal and ASE noise already existing in
the system have identical spectral properties
 Eavesdropper cannot differentiate between the two ASE noises

27. Conclusion
Technique Limitations Advantages
OCDMA Effected by dispersions in
the fiber; hence range of
transmission gets limited to
no longer than 100 km [3].
It is a multiple access
system; plurality of codes
can exist in the same
channel.
Confidentiality is not as
strong as that provided by
data encryption.
Chaos based encryption Synchronization of receiver
and transmitter is critical to
proper functioning. It is very
difficult to get lasers of the
same parameters for
synchronization.
There is high level of
robustness at high bit rates
It can create jamming as
well as avoid jamming to a
high degree.
Quantum cryptography Use of amplifiers will
change the qubits. Hence
the range of transmission is
limited.
This method can notify of
interception of data [12].
It needs a dedicated channel
of high quality for key
exchange between every
pair of sender and receiver.
Hence multiplexing is not
possible.
Very vulnerable to
jamming.
Optical steganography:
(a) Temporal stretching of
pulse
Data can be intercepted
using tunable dispersion
compensation devices.
Simplest in implementation.
(b) Temporal phase mask Robust against adversary
attacks.
(c) ASE noise Optical delays between
receiver and transmitter
must be matched exactly to
get the stealth signal.
Public channel does not
induce any power penalty
on the stealth channel and
the stealth channel induces
a power penalty of only 0.2-
0.3 dBm on the public
channel.