Comment by wiktor-k | Hacker News Reader

Comment by wiktor-k | Hacker News Reader

SSH agent extensions are really powerful.

I'm maintaining a crate for writing own agents (and clients) and just recently added an example of providing decryption over extensions [0] which, coupled with the other examples, allows using SSH agent as a proxy between OpenPGP Card devices (eg Yubikeys) and OpenPGP encrypted data.

[0]: https://github.com/wiktor-k/ssh-agent-lib/pull/70

Got some really positive feedback about this one: https://chaos.social/@Foxboron/112416348981479022 ;)

> Windows didn't really do Unix sockets until recently so everything there is awful

Sadly the support for Unix sockets on Windows in Rust's standard lib is stuck in a limbo: https://github.com/rust-lang/libs-team/issues/271

Fortunately the built-in Windows' SSH client and agent work over Named Pipes and it's quite easy to communicate with them that way: https://github.com/wiktor-k/ssh-agent-lib#agent

Unfortunately the version included in git for Windows doesn't and you have to emulate sockets using magic files instead...

What is so great about Unix sockets that e.g. a normal TCP socket bound to localhost or even a named pipe can not do properly?

The server can get the calling process info [0], which may be useful for local access control. TCP sockets cannot distinguish clients like that.

[0]: https://docs.rs/tokio/latest/tokio/net/struct.UnixStream.htm...

UNIX Sockets are more flexible than named pipes;

* You can use them for more than two processes communicating (eg. a server process with potentially multiple client processes connecting);

* They are bidirectional;

* They support passing kernel-verified UID / GID credentials between processes;

* They support passing file descriptors between processes;

* They support packet and sequenced packet modes.

TCP only grants you 2 of these extra features (sequenced packet mode/bidirection), leaving a giant hole in security in the process.

The named pipes, at least on Windows, also support all of that except for passing UID/GID and file handles.

AFAIR you can choose to use Windows OpenSSH or the other one during Git for Windows installation. [0]

[0]: https://duckduckgo.com/?q=git+for+Windows+openssh&t=fpas&iax...

Unfortunately it's difficult to enforce that, so dealing with users who've already set things up in a specific way is a problem

could always ship a static linked ssh_client

How hard would that be to extend that to include PKCS#11?

The SSH agent shipped with OpenSSH already includes PKCS#11 support (check out the `-s` flag). I'm using that daily to work with TPM-backed keys.

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