Threat Modeling Encrypted Databases

Adrian Colyer has an interesting summary of a recent paper, “Why your encrypted database is not secure” in his excellent “morning paper” blog.

If we can’t offer protection against active attackers, nor against persistent passive attackers who are able to simply observe enough queries and their responses, the fallback is to focus on weaker guarantees around snapshot attackers, who can only obtain a single static observation of the compromised system (e.g., an attacker that does a one-off exfiltration). Today’s paper pokes holes in the security guarantees offered in the face of snapshots attacks too.

Many recent encrypted databases make strong claims of “provable security” against snapshot attacks. The theoretical models used to support these claims are abstractions. They are not based on analyzing the actual information revealed by a compromised database system and how it can be used to infer the plaintext data.

I take away two things: first, there’s a coalescence towards a standard academic model for database security, and it turns out to be a grounded model. (In contrast to models like the random oracle in crypto.) Second, all models are wrong, and it turns out that the model of a snapshot attacker seems…not all that useful.