// host key warning
if you see a warning like this when connecting, don't panic — here's what it means and how to fix it.
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ @ 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)!
// should i worry?
our ssh host key is persistent across regular updates. normal deploys do not change the key, so you should not see this warning after a routine update.
if the host key ever does need to change (e.g. a server migration), we will announce it on the /updates page beforehand. if you see this warning and there's no announcement — be cautious.
// why does this happen?
every ssh server has a unique key that identifies it. your computer remembers this key the first time you connect. if the key changes, your ssh client warns you — this is a security feature to protect you from man-in-the-middle attacks.
common reasons for a key change:
server migration
we moved to a new server (announced on /updates)
infrastructure change
a major change required regenerating the key (also announced)
actual attack
if there's no announcement, treat this seriously
// how to fix it
first, check the /updates page to confirm a host key change was announced. if it was, remove the old key:
then connect again as usual:
you'll be asked to accept the new key — type yes and you're good to go.
// manual fix
if ssh-keygen -R doesn't work, you can manually edit the file:
open the known hosts file
~/.ssh/known_hosts on macOS and Linux
find the line containing chessssh.com
it will be a long line starting with the hostname
delete that line and save
then reconnect with ssh chessssh.com
// windows (PuTTY)
if you're using PuTTY, you'll see a dialog box about the server's host key. click Yes to accept the new key and continue.
if you want to clear it manually, the keys are stored in the Windows Registry under:
// no announcement but got the warning?
if you see a host key warning and there is no matching announcement on /updates, this could indicate a man-in-the-middle attack. here's what you should do:
do not accept the new key
when your ssh client asks to continue, type no or press Ctrl+C
do not enter your password
if someone is intercepting the connection, they could capture your credentials
check your network
public wifi, hotel networks, and shared connections are common targets for MITM attacks. try again from a trusted network
try again later
if the warning persists on a trusted network, it may be a temporary issue on our end — check /updates again in a few hours
if you use chessssh on untrusted networks regularly, consider using a VPN to protect your connection.