Any system, running OpenSSH 8.8 or newer disables RSA signatures using the SHA-1 hash algorithm by default. When you will try to use the SSH key generated using the ssh-rsa sha-1 hash algorithm, the SSH key isn't accepted (the user receives a 'Permission denied' message) or the following message in ssh verbose mode (ssh -v):
debug1: send_pubkey_test: no mutual signature algorithm
Considering that the Virtuozzo Application Platform implemented support of ECDSA keys in a 8.0-2 Platform version, it can affect the connection via SSH gate on a previous one and there is a workaround, that can be used for it:
In order to re-enable the support of RSA keys, you can modify your local ssh client configuration file ~/.ssh/config (create this file, if it does not exist)
Host GATE IdentityFile ~/.ssh/rsa HostKeyAlgorithms +ssh-rsa PubkeyAcceptedAlgorithms +ssh-rsa
"GATE" - should be replaced with a gate hostname, you can find it in the User settings, as on a screenshot:
IdentityFile path ~/.ssh/rsa - should be replaced with a path to your private RSA key, used for SSH connection, e.g. ~/path/to/your/key.
Or you can simply put this single line to the ~/.ssh/config, it will allow using RSA keys for all SSH connections (less recommended):