Clarify Secretkeeper comments

     * Retrieve the instance of the `IAuthGraphKeyExchange` HAL that should be used for shared

     * session key establishment. These keys are used to perform encryption of messages as

     * described in SecretManagement.cddl, allowing the client and Secretkeeper to have a

     * cryptographically secure channel.

     * cryptographically secure channel. In the key exchange protocol the client acts as P1

     * (source) and Secretkeeper as P2 (sink). The interface returned here can be used to invoke

     * methods on the sink.

     *

     * The client's identity is its DICE chain; Secretkeeper's identity is a

     * per-boot key pair.

     */

    IAuthGraphKeyExchange getAuthGraphKe();

     * ProtectedRequestPacket & ProtectedResponsePacket using symmetric keys agreed between

     * the client & service. This cryptographic protection is required because the messages are

     * ferried via Android, which is allowed to be outside the TCB of clients (for example protected

     * Virtual Machines). For this, service (& client) must implement a key exchange protocol, which

     * is critical for establishing the secure channel.

     * Virtual Machines). For this, service (& client) must implement the AuthGraph key exchange

     * protocol to establish a secure channel between them.

     *

     * If an encrypted response cannot be generated, then a service-specific Binder error using one

     * of the ERROR_ codes above will be returned.

    ; Requested Entry not found.

    ErrorCode_EntryNotFound: 3,

    ; Error happened while serialization or deserialization.

    SerializationError: 4,

    ErrorCode_SerializationError: 4,

    ; Indicates that Dice Policy matching did not succeed & hence access not granted.

    ErrorCode_DicePolicyError: 5,

)

    GetSecretResult,

)

GetVersionResult = (version : uint)

GetVersionResult = (1)

StoreSecretResult = ()