Re: Unable to exchange encryption keys

On Mon, 24 Nov 2025, Werner Stolz via curl-users wrote:

> We first encountered this error in 2022, and the only suggestion was to 
> upgrade our version of curl.  We have now done that, and the problem 
> actually seems WORSE.

As you're using SFTP, I think this problem is within libssh2 and that a curl 
update does almost nothing for improving this case.

> * libssh2 cryptography backend: openssl compatible
> * User: USER
> * Failure establishing ssh session: -5, Unable to exchange encryption keys
> * closing connection #0
> curl: (2) Failure establishing ssh session: -5, Unable to exchange encryption keys

This is libssh2 returning an error when it fails to establish an SSH session 
with the server.

libssh2 is an understaffed and resource drained project. I propose you roll up 
your sleeves and do some debugging of your own, and maybe check with other 
libssh2 users if they have seen something similar.

-- 

  / daniel.haxx.se || https://rock-solid.curl.dev
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