SilcMessagePayload
    silc_message_payload_parse(unsigned char *payload,
                               SilcUInt32 payload_len,
                               SilcBool private_message,
                               SilcBool static_key,
                               SilcCipher cipher,
                               SilcHmac hmac,
                               unsigned char *sender_id,
                               SilcUInt32 sender_id_len,
                               unsigned char *receiver_id,
                               SilcUInt32 receiver_id_len,
                               SilcStack stack,
                               SilcBool no_allocation,
                               SilcMessagePayload message);

    Parses Message Payload returning new payload structure.  This also
    decrypts the payload and checks the MAC.  If the payload is
    channel message then `private_message' is FALSE, and if it is
    private message it is TRUE.  If the private message key is static
    (pre-shared key) then protocol dictates that the IV is present
    and `static_key' must be set to TRUE.  If the key is not static
    (Key Agreement was done for the key) then it MUST be FALSE.  For
    channel messages the `static_key' is ignored.

    If the `hmac' is no provided then the MAC of the channel message is
    not verified.  If the message is private message and `cipher' is NULL
    then this assumes that the packet was decrypted with session keys
    (no private message key) and this merely decodes the payload.

    The `sender_id' and `receiver_id' are the IDs from the packet header
    of the packet where this message payload was received.

    If the `message' is non-NULL then that pre-allocated context is
    used in parsing.  Same context is returned.  Otherwise new context
    is allocated and returned.  If the `stack' is non-NULL then memory
    is allocated from that stack.  If `no_allocation' is TRUE then the
    `message' must be provided and data is merely parsed and referenced
    from `payload' and will become invalid when `payload' invalidates.
    If `no_allocation' is TRUE the routine does not do any allocations.