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LFCS · Question #396

A user is attempting to connect to a remote server via SSH and receives the following message: The authenticity of host 'mail.example.com (208.77.188.166)' can't be established. RSA key fingerprint…

The correct answer is D. The server's SSH host key cannot be found in the list of known hosts. This message indicates that the SSH client has not previously encountered or stored the remote server's host key fingerprint in its known_hosts file.

Submitted by asante_acc· Apr 18, 2026Networking

Question

A user is attempting to connect to a remote server via SSH and receives the following message: The authenticity of host 'mail.example.com (208.77.188.166)' can't be established. RSA key fingerprint is 92:32:55:e9:c4:20:ae:1b:2c:d7:91:40:90:89:1c:ad. Are you sure you want to continue connecting (yes/no)? What does this indicate?

Options

  • AThe RSA key fingerprint was found in the SpamCop database, indicating that the remote host is a
  • BThe user's SSH client was unable to connect to the remote host's authentication agent for verification.
  • CThe user's SSH client is incompatible with the server's RSA key.
  • DThe server's SSH host key cannot be found in the list of known hosts.

How the community answered

(18 responses)
  • A
    6% (1)
  • B
    6% (1)
  • D
    89% (16)

Why each option

This message indicates that the SSH client has not previously encountered or stored the remote server's host key fingerprint in its `known_hosts` file.

AThe RSA key fingerprint was found in the SpamCop database, indicating that the remote host is a

SSH host key fingerprints are not checked against a SpamCop database; this is unrelated to the SSH host key verification process.

BThe user's SSH client was unable to connect to the remote host's authentication agent for verification.

This message does not relate to an authentication agent; it is specifically about verifying the identity of the remote host itself based on its host key.

CThe user's SSH client is incompatible with the server's RSA key.

The client is compatible with the server's key, as it successfully received and displayed the RSA key fingerprint, it just hasn't verified its authenticity against known keys.

DThe server's SSH host key cannot be found in the list of known hosts.Correct

The "authenticity of host can't be established" warning means the SSH client has received the server's host key, but this key is not present in the user's `~/.ssh/known_hosts` file (or the system's global `ssh_known_hosts`), indicating it's the first connection or the key has changed.

Concept tested: SSH host key verification

Source: https://man7.org/linux/man-pages/man1/ssh.1.html

Topics

#SSH#Host Keys#Known Hosts

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