computer science

Proof of secure erasure

Proof of secure erasure 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 Proof of secure erasure rather than just read about it. In short: In computer security, proof of secure erasure (PoSE) or proof of erasure is a remote attestation protocol, by which an embedded device proves to a verifying party, that it has just erased (overwritten) all its writable memory. The purpose is to make sure that no malware remains in the device.

Key takeaways

Proof of secure erasure 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 Proof of secure erasure to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Proof of secure erasure from memory before moving on to harder problems.

Reference excerpt

In computer security, proof of secure erasure (PoSE) or proof of erasure is a remote attestation protocol, by which an embedded device proves to a verifying party, that it has just erased (overwritten) all its writable memory. The purpose is to make sure that no malware remains in the device. After that typically a new software is installed into the device.

Overview The verifying party may be called the verifier, the device being erased the prover. The verifier must know the device's writable memory size from a trusted source and the device must not be allowed to communicate with other parties during execution of the protocol, which proceeds as follows. The verifier constructs a computational problem, which cannot be solved (in reasonable time or at all) using less than the specified amount of memory, and sends it to the device. The device responds with the solution and the verifier checks its correctness.

Protocol constructions

Naive approach In the simplest implementation the verifier sends a random message as large as the device's memory to the device, which is expected to store it. After the device has received the complete message, it is required to send it back. Security of this approach is obvious, but it includes transfer of a huge amount of data (twice the size of the device's memory). This can be halved if the device responds with just a hash of the message. To prevent the device from computing it on the fly without actually storing the message, the hash function is parametrized by a random value sent to the device after the message.

Communication-efficient constructions Avoiding the huge data transfer requires a suitable (as stated in Overview) computational problem, whose description is short. Dziembowski et al. achieve this by constructing what they call an (m − δ, ε)-uncomputable hash function, which can be computed in quadratic time using memory of size m, but with memory of size m − δ it can be computed with at most a negligible probability ε.

Communication- and time-efficient constructions Karvelas and Kiayias claim to have designed the first PoSE with quasilinear time and sublinear communication complexity.

Relation to proof of space Proof of space is a protocol similar to proof of secure erasure in that both require the prover to dedicate a specific amount of memory to convince the verifier. Nevertheless, there are important differences in their design considerations. Because the purpose of proof of space is similar to proof of work, the verifier's time complexity must be very small. While such property may be useful for proof of secure erasure as well, it is not fundamental to its usefulness. Proof of secure erasure on the other hand requires the prover to be unable to convince the verifier using less than the specified amount of memory. Even this may be useful for the other protocol, however proof of space is not harmed if the prover may succeed even with significantly less space.

References

Worked examples

Example 1 — a first encounter with Proof of secure erasure

Start with the simplest possible case. Write down what Proof of secure erasure 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 Proof of secure erasure 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 Proof of secure erasure 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 Proof of secure erasure

In research: Proof of secure erasure 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 Proof of secure erasure 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: Proof of secure erasure is common in secondary-school and first-year university syllabi. It links to neighbouring topics Communications protocols, Computer security procedures, Cryptographic protocols, so understanding it makes those chapters shorter.
In everyday life: Look for Proof of secure erasure 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 Proof of secure erasure in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Proof of secure erasure 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 Proof of secure erasure out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Proof of secure erasure in simple terms?

Why does Proof of secure erasure 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 Proof of secure erasure?

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 Proof of secure erasure.