KB ID 0001245
I thought my RoyalTSX had broken today, I upgraded it a couple of weeks ago, and I upgraded to macOS Catalina 10.15 the other day. After this, all my SSH sessions refused to connect with this error;
Unable to negotiate with x.x.x.x port 22: no matching key exchange found. Their offer diffie-hellman-group1-sha1
Note: You may also see the following error;
Unable to negotiate with x.x.x.x port 22: no matching cipher found. Their offer: aes128-cbc,3des-cbc,aes192-cbc,aes256-cbc
This is not Apple’s fault, it’s OpenSSH version 7. SHA1 is weak, so support for it has been removed. Which is fine, but all my clients Cisco Firewalls/Routers/Switches are probably all using RSA/SHA1. So until they re all updated I’m going to need to re-enable SHA1.
Open a terminal windows and execute the following;
sudo nano /etc/ssh/ssh_config ENTER YOUR PASSWORD
Locate the line ‘ # MACs hmac-md5,hmac-sha1,email@example.com,hmac-ripemd160′ and remove the Hash/Pound sight from the beginning.
Locate the line ‘ # Ciphers aes128-ctr,aes192-ctr,aes256-ctr,aes128-cbc,3des-cbc’ and remove the Hash/Pound sight from the beginning.
Then paste the following on the end;
Theres no reason to reboot, it should work straight away.
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