44r0n7
0265afa054
Import the runnable game code, content, docs, scripts, and repo guidance while leaving local agent state, dependency installs, build output, and backup copies out of the published tree.
39 lines
2.6 KiB
JSON
39 lines
2.6 KiB
JSON
{
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"id": "ssh-keys",
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"title": "SSH Key Authentication",
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"category": "access",
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"tags": ["ssh", "authorized_keys", "keys", "permissions"],
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"updated": "2025-11-03",
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"summary": "How SSH key auth works and how to set it up correctly.",
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"sections": [
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{
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"heading": "How It Works",
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"body": "<p>SSH key authentication replaces passwords with a cryptographic key pair. The <strong>private key</strong> stays on your machine. The <strong>public key</strong> goes into <code>~/.ssh/authorized_keys</code> on the target host. When you connect, the server checks whether your private key corresponds to one of the public keys it trusts.</p><p>There is no password transmitted. Either the key matches or the connection fails.</p>"
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},
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{
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"heading": "Generating a Key Pair",
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"body": "<p>Use <code>ed25519</code> unless something forces you onto RSA. It is smaller and more secure.</p>",
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"code": "ssh-keygen -t ed25519 -C \"your-comment-here\"\n# Accept the default path (~/.ssh/id_ed25519) or specify one.\n# Passphrase is optional but recommended for keys that leave your machine."
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},
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{
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"heading": "Installing the Public Key",
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"body": "<p>Copy the public key to the remote host:</p>",
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"code": "# Option 1 — if password auth is still working\nssh-copy-id -i ~/.ssh/id_ed25519.pub user@host\n\n# Option 2 — manually\ncat ~/.ssh/id_ed25519.pub >> ~/.ssh/authorized_keys"
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},
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{
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"heading": "File and Directory Permissions",
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"body": "<p>This is the most common reason key auth fails. SSH will silently reject keys if the permissions are too open.</p>",
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"code": "chmod 700 ~/.ssh\nchmod 600 ~/.ssh/authorized_keys\nchown -R youruser:youruser ~/.ssh"
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},
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{
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"heading": "Troubleshooting",
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"body": "<p>Run <code>ssh -v user@host</code> for verbose output. The auth failure reason is usually in the first 20 lines.</p><p>Common causes:</p><ul><li><code>authorized_keys</code> file has wrong permissions (see above)</li><li><code>~/.ssh</code> directory is world-writable</li><li><code>authorized_keys</code> file does not exist</li><li>The file exists but is empty or the key was pasted with a line break in the middle</li><li><code>sshd_config</code> has <code>PubkeyAuthentication no</code></li></ul>"
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},
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{
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"heading": "Checking the sshd Config",
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"body": "<p>Relevant lines in <code>/etc/ssh/sshd_config</code>:</p>",
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"code": "PubkeyAuthentication yes\nAuthorizedKeysFile .ssh/authorized_keys\n\n# After editing sshd_config, test before reloading:\nsshd -t\nsystemctl reload ssh"
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}
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]
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}
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