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I'm Jason, a web applications developer in the San Francisco Bay area.

SSH issues with Mac OS X High Sierra

A coworker of mine was reporting an issue with SSH after updating to Mac OS X High Sierra.

$ ssh server-alias-hostname
Unable to negotiate with port 22: no matching cipher found. Their offer: blowfish-cbc,aes256-cbc

You can view a list of supported ciphers by running ssh -Q cipher.

It turns out that the system is configured to use certain ciphers within /etc/ssh/ssh_config. You can adjust your local configuration within ~/.ssh/config to make sure that the ciphers supported by your local client match one of the ones offered by the remote server.

# ~/.ssh/config
Host *
  SendEnv LANG LC_*
  Ciphers +aes256-cbc