One-time recovery credentials for encrypted data access

One or more computer storage media having stored thereon multiple instructions that, when executed by one or more processors of a device, cause the one or more processors to:

• receive a first one-time recovery credential that is one of multiple one-time recovery credentials in a sequence of one-time recovery credentials, previous one-time recovery credentials in the sequence being indeterminable given subsequent one-time recovery credentials in the sequence;
• decrypt, using the first one-time recovery credential, a key encrypted with the first one-time recovery credential and associated with the device;
• and
• use the key to decrypt encrypted data stored on a first storage media of the device.

A method implemented in a key recovery service, the method comprising:

• receiving from an intermediary, via an unsecure communication channel, a key recovery request for a device;
• identifying a recovery key associated with the device;
• identifying, from the key recovery request, a particular one-time recovery credential in a sequence of multiple one-time recovery credentials, previous one-time recovery credentials in the sequence being indeterminable given subsequent one-time recovery credentials in the sequence, the particular one-time recovery credential being identified by one of multiple sequential numbers, each of the multiple sequential numbers being associated with one of the multiple one-time recovery credentials in the sequence;
• generating, by the key recovery service, the particular one-time recovery credential in the sequence by generating an initial one-time recovery credential in the sequence by using the recovery key as an input to a one-way hash function, and generating subsequent one-time recovery credentials in the sequence until the particular one-time recovery credential is generated by repeatedly providing a previous output of the one-way hash function as an input to the one-way hash function;
• and
• returning to the intermediary, via an unsecure communication channel, the particular one-time recovery credential in response to the key recovery request.