SSH Changes in May 2019
What Changed?
During the 29-30 May 2019 shutdown, we made the following ssh security improvements on Niagara:
- Disabled certain weak encryption algorithms.
- Disabled certain weak public key types.
- Regenerated Niagara's host keys.
Updating your client's known host list
The first time you login to Niagara after the shutdown, you will probably see the following warning 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 ED25519 key sent by the remote host is SHA256:SauX2nL+Yso9KBo2Ca6GH/V9cSFLFXwxOECGWXZ5pxc. Please contact your system administrator. Add correct host key in /home/username/.ssh/known_hosts to get rid of this message. Offending ECDSA key in /home/username/.ssh/known_hosts:109 ED25519 host key for niagara.scinet.utoronto.ca has changed and you have requested strict checking. Host key verification failed. Killed by signal 1.
This warning is displayed because the host keys on Niagara changed to increase the data centres security, and ssh clients remember old host keys to prevent "man-in-the-middle" attacks.
You may also get a warning regarding "DNS spoofing", which is related to the same change.
If you are using MobaXTerm or Putty as your ssh client under Windows, the warning will appear in a pop-up window and will allow you to accept the new host key by clicking "Yes".
If you are using the command line ssh command on macOS, Linux, GitBash or Cygwin, you should tell your system to "forget" the old host keys, by running the following commands:
$ ssh-keygen -R niagara.scinet.utoronto.ca $ ssh-keygen -R niagara.computecanada.ca $ ssh-keygen -R 142.150.188.70
Afterwards, the next time you ssh to Niagara you'll be asked to confirm the new host keys, e.g.:
$ ssh niagara.scinet.utoronto.ca The authenticity of host 'niagara.scinet.utoronto.ca (142.150.188.70)' can't be established. ED25519 key fingerprint is SHA256:SauX2nL+Yso9KBo2Ca6GH/V9cSFLFXwxOECGWXZ5pxc. ED25519 key fingerprint is MD5:b4:ae:76:a5:2b:37:8d:57:06:0e:9a:de:62:00:26:be. Are you sure you want to continue connecting (yes/no)?
Make sure the fingerprints are correct! You'll either see the above ED25519 fingerprints, or the following RSA fingerprints:
RSA key fingerprint is SHA256:k6YEhYsI73M+NJIpZ8yF+wqWeuXS9avNs2s5QS/0VhU. RSA key fingerprint is MD5:98:e7:7a:07:89:ef:3f:d8:68:3d:47:9c:6e:a6:71:5e.
If the fingerprints don't match, someone may be trying to hijack your connection.
WINSCP?
Troubleshooting
I can't connect!
If you see one of the following error messages:
Unable to negotiate with 142.150.188.70 port 22: no matching cipher found. Unable to negotiate with 142.150.188.70 port 22: no matching key exchange method found. Unable to negotiate with 142.150.188.70 port 22: no matching mac found.
you need to upgrade your ssh client.
My SSH key no longer works
If you're being asked for a password, but were using SSH keys, it's because 1024-bit DSA & RSA keys have been disabled.
You need to generate a new stronger key, see the SSH keys page for details.