Protecting an SSH private key | LinuC Level 1 102 Exam original practice question

1.10.3Basic

Make ~/.ssh/id_ed25519 readable and writable only by its owner.

Which command is appropriate?

Hint 1: Focus on the key relationship

Identify who must decrypt the data, then distinguish confidentiality, authentication, and the direction of each key operation.

Hint 2: Key terms

Review the short definitions of SSH keys, forwarding directions, encryption, and signatures involved.

SSH private key: Secret information used for SSH authentication or signing and not shared with others.
0600: A mode that grants read/write access to the owner and no permissions to group or others.
chmod: A command that changes a file's permission mode.
Public key: The distributable key paired with a private key.
File permission: The owner, group, and other access attributes for a file.

Detailed explanation

Incorrectchmod 644 ~/.ssh/id_ed25519

Incorrect. 644 lets group and other users read the private key.

Incorrectchmod 755 ~/.ssh/id_ed25519

Incorrect. 755 grants broad read and execute permissions.

Correctchmod 600 ~/.ssh/id_ed25519

Correct. 600 permits only owner read/write.

Incorrectchmod 400 ~/.ssh/id_ed25519.pub

Incorrect. It targets the public key and changes neither the private key nor its required mode.

An example you can run in a temporary verification environment.

tmp=$(mktemp -d); printf 'private' > "$tmp/id_ed25519"; chmod 600 "$tmp/id_ed25519"; stat -c '%a' "$tmp/id_ed25519"; rm -rf "$tmp"

Foundation review

A server identity key used by SSH clients to detect a changed endpoint.

A key pair used to authenticate a user to an SSH server.

An SSH tunnel that carries traffic between a local, remote, or dynamic endpoint.

Question IDKL-102-1150

EnvironmentGNU coreutils / 一時ディレクトリ

Last technical review2026-08-20

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