Can't connect to a SSH server using secure cipher settings

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
30/100
Issue type
Bug
Clarity
Needs clarification
Activity status
Stale
Tech stack
c
Domain
networking

Research direction

Start by reproducing the connection failure against a server using the listed KexAlgorithms, Ciphers, and MACS settings, then collect SSHFS-Win or underlying SSH negotiation logs. Compare the negotiated algorithm requirements with the client's supported settings; done means sshfs-win connects successfully to the hardened server. No source files or tests are named in the issue.

Written by the indexing model from the issue text.

Description

We have all our SSH servers hardened using the recommendations from ssh-audit:

 https://github.com/jtesta/ssh-audit

In particular, our SSH servers have the following cipher config:

 KexAlgorithms curve25519-sha256@libssh.org,diffie-hellman-group18-sha512,diffie-hellman-group16-sha512,diffie-hellman-group14-sha256
 Ciphers aes256-gcm@openssh.com,aes128-gcm@openssh.com,chacha20-poly1305@openssh.com,aes256-ctr,aes192-ctr,aes128-ctr
 MACS hmac-sha2-512-etm@openssh.com,hmac-sha2-256-etm@openssh.com,umac-128-etm@openssh.com

sshfs-win cannot connect to those servers when using a hardened config. I've tested using SSHFS-Win 2021.1 Beta2/WinFsp 2021 on a fully-updated Win 10 server.

If there's any debugging or log info I can provide, please let me know.

Dominant language
C
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