ECE 6605 - Information Theory
Prof. Matthieu Bloch
Tuesday, November 21, 2023
Announcements
- Project
- Send me an email to confirm your choices (the sooner the
better)
- I'll hold project office hours to help you
- Exam options
- Oral: list of problems published, scheduling options coming
- Written: Thursday, December 14 11:20 am - 2:10 pm
- Last time
- Soft covering channel resolvability
- (skipped converse proof)
- Today
Shannon Cipher System
Shannon Cipher system
- Historical paper: Claude E. Shannon, Communication
Theory of Secrecy Systems, Bell System Technical Journal, (1948)
- Secrecy metric: - message and
ciphertext should be statisticall independent
- If true, the best attack is to guess the message
- How is this possible? Secret key is required
- One-time pad, see assignments
- How much key do we need?
Wiretap channel
Wyner's wiretap channel
- Historical paper: A. D. Wyner, The Wire-Tap
Channel, Bell System Technical Journal, (1975)
- Physically degraded channel (can be relaxed, more complicated)
- Secrecy metric:
(asymptotic independence)
A code for a wiretap channel consists of
an encoding function and a
decoding function
- The performance of an
code is measured in terms of
- The rate of the code (bits/source symbol)
- Reliability and secrecy and
Wiretap channel
For a physically degraded discrete memoryless channel characterized
by and ,
- Challenges
- How do we operationalize secrecy?
- Can we leverage the coding mechanisms studied earlier?
Secret key generation
Secret key generation from correlated observations
- Public authenticated channel of unlimited capacity available for
reocnciliation
A code for secret-key generation consists
of an encoding function and a decoding function
- The performance of an
code is measured in terms of
- The rate of the code (bits/source symbol)
- Reliability and secrecy and
Secret key generation
For a physically degraded discrete memoryless channel characterized
by and ,
- Not different from secrecy capacity, but this is an artefact of
physically degraded channels
- In general, secret key generation rates are higher than wiretap
coding rates.
- Challenges
- How do we operationalize secrecy?
- Can we leverage the coding mechanisms studied earlier?


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ECE 6605 - Information Theory
Prof. Matthieu Bloch
Tuesday, November 21, 2023