computer science

Subliminal channel

Subliminal channel is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Subliminal channel rather than just read about it. In short: In cryptography, subliminal channels are covert channels that can be used to communicate secretly in normal looking communication over an insecure channel. Subliminal channels in digital signature crypto systems were found in 1984 by Gustavus Simmons.

Key takeaways

Subliminal channel belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Subliminal channel to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Subliminal channel from memory before moving on to harder problems.

Reference excerpt

In cryptography, subliminal channels are covert channels that can be used to communicate secretly in normal looking communication over an insecure channel. Subliminal channels in digital signature crypto systems were found in 1984 by Gustavus Simmons. Simmons describes how the "Prisoners' Problem" can be solved through parameter substitution in digital signature algorithms.

Examples An easy example of a narrowband subliminal channel for normal human-language text would be to define that an even word count in a sentence is associated with the bit "0" and an odd word count with the bit "1". The question "Hello, how do you do?" would therefore send the subliminal message "1". The Digital Signature Algorithm has one subliminal broadband and three subliminal narrow-band channels

Improvements A modification to the Brickell and DeLaurentis signature scheme provides a broadband channel without the necessity to share the authentication key. The Newton channel is not a subliminal channel, but it can be viewed as an enhancement.

Countermeasures With the help of the zero-knowledge proof and the commitment scheme it is possible to prevent the usage of the subliminal channel. This countermeasure has a 1-bit subliminal channel because for is the problem that a proof can succeed or purposely fail. Another countermeasure can detect, and not prevent, the subliminal usage of the randomness.

Notes

References

External links Seminar: "Covert Channels and Embedded Forensics"

Worked examples

Example 1 — a first encounter with Subliminal channel

Start with the simplest possible case. Write down what Subliminal channel claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Subliminal channel before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Subliminal channel ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Subliminal channel

In research: Subliminal channel appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Subliminal channel in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Subliminal channel is common in secondary-school and first-year university syllabi. It links to neighbouring topics Cryptography, so understanding it makes those chapters shorter.
In everyday life: Look for Subliminal channel outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Subliminal channel in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Subliminal channel means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Subliminal channel out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Subliminal channel in simple terms?

Why does Subliminal channel matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Subliminal channel?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Subliminal channel.