Troubleshooting Tip: SSH error 'No matching host key type found. Their offer:'

[mle2802]

Description	This article describes the solution for the SSH error 'No matching host key type found. Their offer:' After upgrading to v7.2.6.
Scope	FortiGate FOS v7.2.6.
Solution	Upon taking a packet capture, it may be seen that FortiGate did not send any host key-type proposal: To diagnose SSH Key exchange issues on Fortigate, use the following debug commands: diagnose debug console timestamp enable diagnose debug application sshd -1 diagnose debug enable The 'list_hostkey_types' is empty: SSH: fd 7 is not O_NONBLOCK SSH: Forked child 31816. SSH: Client protocol version 2.0; client software version PuTTY_Release_0.68 SSH: no match: PuTTY_Release_0.68 SSH: Enabling compatibility mode for protocol 2.0 SSH: Local version string SSH-2.0-Nn0FjQVd-y SSH: fd 7 setting O_NONBLOCK SSH: Proposal: 0, Ciphers: 'diffie-hellman-group14-sha1' SSH: Proposal: 2, Ciphers: 'chacha20-poly1305@openssh.com,aes256-ctr,aes256-gcm@openssh.com' SSH: Proposal: 3, Ciphers: 'chacha20-poly1305@openssh.com,aes256-ctr,aes256-gcm@openssh.com' SSH: Proposal: 4, Ciphers: 'hmac-sha2-256,hmac-sha2-256-etm@openssh.com,hmac-sha2-512,hmac-sha2-512-etm@openssh.com' SSH: Proposal: 5, Ciphers: 'hmac-sha2-256,hmac-sha2-256-etm@openssh.com,hmac-sha2-512,hmac-sha2-512-etm@openssh.com' SSH: list_hostkey_types: This happens because the host key file may be deleted or corrupted during an update. It is possible to check by using the following command: 'fnsysctl ls -l /etc/ssh'. In this case, the solution is regenerating SSH host keys by using the command 'execute ssh-regen-keys'. After this, reconnect SSH and see if the connection is going through. Related articles: Technical Tip: 'No matching key exchange found' Technical Tip: SSH key exchange troubleshooting Technical Tip: How SSH Server host key algorithms can be changed  Technical Tip: SSH Server host key offered by FortiGate