Agent Protocol Notes

Overview

The SSH agent protocol uses a four-byte big-endian length prefix followed by a message body. SSHAgent builds those frames for identity and signing requests, and SSHAgentResponseHandler accumulates inbound bytes until a complete response frame is available.

Identity responses are parsed into SSHAgentKey values by decoding the key blob and comment for each entry. Signature responses are validated against the expected response type before the embedded signature payload is extracted. RSA signatures are then converted into the NIOSSHSignature cases expected by the currently selected swift-nio-ssh branch.

The implementation favours explicit parsing over generic decoding helpers because the on-the-wire representation is small, fixed, and performance-sensitive. That makes the protocol easier to audit when support for additional key algorithms is added.