Revisiting Shared Data Protection Against Key Exposure

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Video file (mp4)

The gist

The gist This paper introduces two novel schemes for computational secret sharing that match an all-or-nothing security level under key exposure in distributed storage environments, offering faster

In short

The research introduces two new computational secret sharing schemes, SSAKE and ROSSake, designed to provide 'all-or-nothing' security against key exposure in distributed storage. These schemes are faster than existing methods by reducing processing overhead. SSAKE uses standard block ciphers, while ROSSake uses a random oracle model for zero additional post-processing.

Key concepts

All-or-Nothing (AON) Security
This security level means an adversary learns nothing about the data unless they possess both the entire ciphertext and the secret encryption key. The paper aims to achieve this property efficiently in distributed storage settings where key exposure is a risk.
SAKE Security Model
This new model focuses on compromising servers or sites rather than blocks. It requires that an adversary who compromises one site cannot gain access to other data stored at the same site, ensuring security even with partial server compromise.
SSAKE Scheme
This scheme uses a standard block cipher in CTR mode and involves four steps: encrypting data, transforming the ciphertext with a linear function, splitting it into n fragments, and sharing the initialization vector (IV) using perfect secret sharing to create final shares.
ROSSake Scheme
This alternative scheme avoids extra processing by using a random oracle model. It involves sampling a secret key K, creating a one-time pad with this key and IV, splitting the resulting padded data into n fragments, and combining them with secret shares of the IV.

Terminology used across episodes

This episode discusses

The paper

Revisiting Shared Data Protection Against Key Exposure · Read on arXiv

DOI: 10.1145/3320269.3372198

Transcript

Introduction to the show: ident: Security Radio. Generated commentary on the latest security and cryptography papers.

Nadia: We're looking at the paper: "Revisiting Shared Data Protection Against Key Exposure".

Elias: The gist This paper introduces two novel schemes for computational secret sharing that match an all-or-nothing security level under key exposure in distributed storage environments,

Nadia: First, who's behind it and why it matters.

Title and authors: Nadia: We talked about the title and authors of "Revisiting Shared Data Protection Against Key Exposure," which points to how they are taking the security model and applying it to real distributed storage scenarios.

Elias: The authors are Katarzyna Kapusta, Matthieu Rambaud, and Gerard Memmi. Their work directly addresses how to protect data when keys could be exposed in cloud or multi-cloud environments.

Nadia: What this means for us is that they are moving away from older security models because they realized the old ones weren't efficient enough for the way data is actually stored today.

Elias: It suggests a shift in thinking where we don't look at compromised blocks, but rather how many storage sites an adversary can compromise, which changes the whole approach to sharing secrets.

The paper's summary: Nadia: So the paper summarizes its main point by saying they are proposing a new security model called SAKE where the parameter is the number of compromised servers or sites instead of just blocks.

Elias: They define this as SAKE, and it asks for indistinguishability under chosen plaintext attack and under key exposure for n-one shares in possession of the attacker.

Nadia: This new model is motivated by the idea that if you compromise one block at one site, you can get access to more data stored on that same site because of how storage systems work.

Elias: They also introduce a public randomized keyed invertible transformation called AON, which is what they call an n-SAKE transformation when it meets specific properties.

Nadia: The paper then proposes two schemes to achieve this SAKE security level, one based on standard block cipher encryption and another that uses something like a random oracle or an idealized block cipher.

The paper's improvements: Elias: The paper shows improvements by presenting two specific schemes. First is SSAKE, which uses standard block cipher encryption and it reduces the processing needed for data encryption by half compared to the fastest existing solutions.

Nadia: That means SSAKE is faster than what you'd normally see with AES in this context, which is a big deal for performance in real systems.

Elias: Then they have ROSSake, which ditches the extra processing entirely by switching to something based on random oracles or an idealized block cipher with a key twice as large as the security parameter.

Nadia: So ROSSake completely cuts out that extra post-processing overhead, which is what I was looking for when we talked about efficiency in distributed storage.

Elias: And they benchmarked these against each other, showing that SSAKE is faster than Bastion by reducing the linear overhead by half, while ROSSake is actually the fastest of all SAKE schemes tested.

Conclusion: Nadia: To wrap up, the paper presents SSAKE as a versatile scheme that verifies both security properties for this new model, and ROSSake as an alternative random-oracle based scheme that has no extra processing overhead on top of encryption.

Elias: The main implication is that we have two distinct ways to achieve the all-or-nothing property under key exposure in distributed storage, with one focusing on speed gains and the other on eliminating post-processing costs.

Nadia: For someone just listening to the show, this means there are now concrete technical paths forward for building more robust encryption schemes that can handle the realities of cloud storage.

Elias: We're leaving this discussion here with "Revisiting Shared Data Protection Against Key Exposure," which lays out SSAKE and ROSSake as leading candidates for these new security requirements.

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