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Comment by kba | Hacker News Reader

Why would you assume they wanted FTPS? SFTP is both more common and very superior. Also, what MITM attacks are you afraid of with SFTP?

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> Also, what MITM attacks are you afraid of with SFTP?

SFTP, like SSH, is "trust on first use". If you don't have some out-of-band mechanism in place to verify the server fingerprint, you're going to have a bad time.

While the CA system isn't perfect, rolling out your own CA to clients is easily automated and verifying certificates from that point on happens automatically.

If a client orders SFTP providing off-band fingerprints is a trivial step.

If that client is a single person, sure. If the client is a 500 person organization where half need access to the server, I can see why people would prefer FTPS with a certificate from their internal CA.

You can do SSH certificates that can sign and revoke keys. For some reason, most people assume TLS when you mention the word certificate. Read the CERTIFICATES section in ssh-keygen(1).

True, but you still need to build your own infrastructure to roll out the CA, vs. X.509, which is implicitly handled by all OSes.

You can use regular TLS CA-signed certificates with FTPS, but not with SFTP.

Except yes, you can use CA-signed certificates with SFTP.

You can? And it validates the CA signature? How?

Accordingly: yes, yes, by using appropriate cryptographic algorithm.

I'm not saying one couldn't in theory implement that, but is that actually implemented? Is there any SSH server that accepts an X509 certificate and a client that accepts a database of CA root certs and checks the server cert?

> I'm not saying one couldn't in theory implement that, but is that actually implemented?

I'm not talking about theory here. I'm talking about what OpenSSH can do.

> Is there any SSH server that accepts an X509 certificate and a client that accepts a database of CA root certs and checks the server cert?

Actually, it may not be X.509 per se. I'm not sure if OpenSSH uses precisely X.509 PKI or if it rolls out its own CA implementation, because I don't use this function. I've read somewhere it's the latter case.

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