3.1.5.4.5 PUBLIC_KEY_REQUEST Message
The syntax of this message is specified in section 2.2.2.5.
This is message is targeted to RunspacePool. A server sends this message to get a client's Public Key. After receiving this message, the client MUST send a PUBLIC_KEY message (section 3.1.5.4.3) to the server.
When this message is received, RunspacePool MUST be in Opened state.