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  • Suspicious Message from SSH Server!

    I just got a strange message when I was trying to login! I launched the macOS Terminal app and typed:

    I didn't get the usual password prompt, instead I got this message:

    Unable to negotiate with 192.168.1.2 port 22: no matching key exchange method found. Their offer: diffie-hellman-group-exchange-sha1,diffie-hellman-group1-sha1

    I searched the Internet and found that passing the argument "-oKexAlgorithms=+diffie-hellman-group1-sha1" to the ssh command would pass this message. But when I tried to login with the said argument, I got this message:
    @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
    @ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @
    @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
    IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
    Someone could be eavesdropping on you right now (man-in-the-middle attack)!
    It is also possible that a host key has just been changed.
    The fingerprint for the RSA key sent by the remote host is
    SHA256:qWRhA4Y948bweEJTLM0uYCH6IFUMm9QiA0lnSF6aR0Y.
    Please contact your system administrator.
    Add correct host key in /Users/mac/.ssh/known_hosts to get rid of this message.
    Offending ECDSA key in /Users/mac/.ssh/known_hosts:56
    RSA host key for aratab.com has changed and you have requested strict checking.
    Host key verification failed.

    I have not done anything to the server since I last successfully logged to it yesterday. And the auto-update is turned off. The client also (the macOS system) hasn't been changed as well. Is there something fishy going on in my server?