XK0-005 · Question #810
An administrator has generated an RSA SSH key pair to log in to a remote server. After copying the public key and attempting to log in, the administrator sees the following message…
The correct answer is B. Create a new key pair by running ssh-keygen -t ecdsa. The debug message 'no mutual signature algorithm' indicates the OpenSSH client and server cannot agree on a signing algorithm for the RSA key. Newer versions of OpenSSH (8.8+) disabled the legacy ssh-rsa algorithm (SHA-1) by default due to cryptographic weaknesses. The…
Question
An administrator has generated an RSA SSH key pair to log in to a remote server. After copying the public key and attempting to log in, the administrator sees the following message:
[email protected]: Permission denied (publickey,password) After seeing the message, the administrator attempts to connect using ssh -v [email protected] and notices the following debug output:
debug1: send_pubkey_test: no mutual signature algorithm Which of the following actions should the administrator take first to remediate this issue?
Options
- AIssue systemctl restart sshd on the local server.
- BCreate a new key pair by running ssh-keygen -t ecdsa.
- CSet PermitRootLogin yes in the /etc/ssh/sshd_config file.
- DUpdate permissions on the /home/admin/.ssh directory to 700 on the remote server.
How the community answered
(29 responses)- A3% (1)
- B83% (24)
- C10% (3)
- D3% (1)
Explanation
The debug message 'no mutual signature algorithm' indicates the OpenSSH client and server cannot agree on a signing algorithm for the RSA key. Newer versions of OpenSSH (8.8+) disabled the legacy ssh-rsa algorithm (SHA-1) by default due to cryptographic weaknesses. The immediate fix is to generate a new key pair using a modern algorithm. Running 'ssh-keygen -t ecdsa' creates an ECDSA key, which uses a mutually supported signature algorithm. Option A restarts the local sshd (irrelevant, the issue is the key algorithm). Option C enables root login, which is unrelated to the algorithm mismatch. Option D fixes directory permissions, which would cause a different error, not this algorithm negotiation failure.
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