One way to avoid leaving traces of sensitive user data in the clear on persistent storage is to use cryptographic techniques such as full-disk encryption. Here, the idea is to ensure that all application disk writes are encrypted prior to storage. Therefore, regardless of the nature of the data that is saved to disk, users without knowledge of the corresponding secret key will not be able to recover any information. While this is a powerful and realizable technique, it nevertheless has the significant disadvantage that users can be coerced, through legal or other means, into disclosing their keys, at which point the encryption becomes useless.