Keystore
================================

As stated in the :doc:`../threat_model`, Keystore is a **trusted** server where
users can publish their public keys. You can assume that attackers cannot
overwrite any entry you add to the Keystore.

Keystore is structured as a `key-value store
<https://en.wikipedia.org/wiki/Key-value_database>`_. In this context, key
refers to an unique identifier that is used to index the value in the database,
and does not refer to a crypographic key.

An implementation of Keystore is provided for you (see source code in userlib_)
and is already imported into proj2.go_.

The client application can interact with Keystore using the API documented
below.

.. function:: KeystoreSet(key string, value PKEEncKey/DSVerifyKey) (error)
    
    Stores the given *value* (public cryptographic key) at the given storage
    *key*.
    
    Key-value entries into Keystore are immutable_. Any attempt to
    modify an existing key-value entry will return an error.

    Notice that the required type of *value* is a single public cryptographic
    key; *KeystoreSet* cannot store any other type of data.

    :param key: Unique identifier used to index *value* in the database.
    :type key: string
    :param value: Public (cryptographic) encryption/verification key.
    :type value: PKEEncKey/DSVerifyKey

    :rtype: error

.. function:: KeystoreGet(key string) (value PKEEncKey/DSVerifyKey, ok bool)

    Return the *value* (public cryptographic key) at the given storage
    *key*.
    
    If a value does exist at the given storage *key*, then *ok* will be true;
    otherwise it will be false.

    :param key: Unique identifier used to index *value* in the database.
    :type key: string

    :rtype: PKEEncKey/DSVerifyKey, bool

.. _userlib: https://github.com/cs161-staff/project2-userlib/blob/master/userlib.go
.. _proj2.go: https://github.com/cs161-staff/project2-starter-code/blob/main/proj2.go
.. _immutable: https://en.wikipedia.org/wiki/Immutable_object