1.1. Dataserver

The dataserver is untrusted storage for arbitrary bytes.

It provides a hash map interface (i.e. key-value store interface) between memory location identifiers (see Memloc) and file data (arbitrary bytes). Clients can add data to the dataserver by first requesting a fresh memory location (Memloc, essentially a random string), then adding a new record to the dataserver that maps that location to the desired set of bytes.

All entries in the dataserver exist in a single, global namespace, and dataserver does not perform any access control. As a result, any entry on the dataserver can be overwritten or deleted by any user who knows the corresponding Memloc.

As a reminder, the adversary can persistently observe operations made to either of the servers. Thus, the adversary can observe which users store each \((\mathrm{location}, \mathrm{data})\) pair in each of the servers, the Memlocs used, and the order in which dataserver entries are stored, accessed, or deleted.

dataserver.Set(location: Memloc, value: bytes)

Stores value at location location on the dataserver.

If location already has an existing value, overwrites the old value at location with value.

Parameters:

• location (Memloc) – The location to store value at

• value (bytes) – The value to store at location

Raises:

ValueError – if value is not of type bytes

dataserver.Get(location: Memloc) → bytes

Returns the value stored at location on the dataserver.

Raises an error if location does not exist in the dataserver.

Parameters:

location (Memloc) – The location to retrieve a value from

Raises:

ValueError – if location does not exist in the dataserver

dataserver.Delete(location: Memloc)

Deletes the given value at location from the dataserver, if it exists.

Acts as a no-op if location has no associated value on the dataserver.

Parameters:

location (Memloc) – The location to delete

1.1.1. Extra Testing Functions

For testing purposes only (i.e. you are not permitted to use the API in this section in your client implementation), we also provide the following function:

dataserver.GetMap() → dict[Memloc, bytes]

Returns the entries stored on the dataserver as a Python dictionary.

This may be useful for testing purposes and simulating adversary attacks against your implementation. Specifically, you can compare the entries in the dictionary before (and after) calling a client function and use the difference to deduce where things are stored.

Returns:

The entries stored on the dataserver

Return type:

dict[Memloc, bytes]