SSH Key Management

This page is meant to assist in setting up and maintaining SSH keys.

SSH Directory Permissions

chmod 700 ~/.ssh
chmod 644 ~/.ssh/authorized_keys
chmod 644 ~/.ssh/known_hosts
chmod 644 ~/.ssh/config
chmod 600 ~/.ssh/id_ed25519
chmod 644 ~/.ssh/id_ed25519.pub
chmod 600 ~/.ssh/id_rsa
chmod 644 ~/.ssh/id_rsa.pub

Generating SSH Keys

ED25519

Change to ~/.ssh:
```
cd ~/.ssh
```
Generate an Ed25519 ssh key:
```
ssh-keygen -t ed25519 -a 256
```

Generate an Ed25519 ssh key with a specific name:

ssh-keygen -f <keyname> -t ed25519 -a 256

RSA

Change to ~/.ssh:
```
cd ~/.ssh
```
Generate a RSA ssh key:
```
ssh-keygen -t rsa -b 4096 -o -a 256
```

Generate a RSA ssh key with a specific name:

ssh-keygen -f <keyname> -t rsa -b 4096 -o -a 256

Verifying SSH Keys

Verify SSH Key Password

Change to ~/.ssh:
```
cd ~/.ssh
```
Verify password:
```
ssh-keygen -y -f id_ed25519
```

Upon entering successful passphrase, it prints the pubkey:

Enter passphrase: 
ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIJAZcdEIpPbJal7CEsIpaHzBEjs/8nedIvDA/sDlvqll chuck@gaming

Enter the wrong passphrase:

ssh-keygen -y -f id_ed25519
Enter passphrase: 
Load key "id_ed25519": incorrect passphrase supplied to decrypt private key

Verify SSH Private Key Matches Public Key

Change to ~/.ssh:
```
cd ~/.ssh
```

Verify ssh key matches it's private key:

ssh-keygen -l -f id_ed25519; ssh-keygen -l -f id_ed25519.pub

Output should match:

256 SHA256:W5o5+DV3Jaba4txzQ58gZuIZvZD44McIU7tV9I4LZpw chuck@gaming (ED25519)
256 SHA256:W5o5+DV3Jaba4txzQ58gZuIZvZD44McIU7tV9I4LZpw chuck@gaming (ED25519)

Modifying SSH Keys

Change SSH Key Password

Change to ~/.ssh:
```
cd ~/.ssh
```
Change password:
```
ssh-keygen -p -f id_ed25519
```

Change SSH Key Comment

Change to ~/.ssh:
```
cd ~/.ssh
```

Change comment (email):

ssh-keygen -c -f id_ed25519
Enter passphrase: 
Key now has comment 'chuck@hostname'
Enter new comment: user@newname
The comment in your key file has been changed.

SSH-Agent

Add the key to the ssh-agent.
```
ssh-add keyname
```
Add the key to the server using the credentials from the config file.
```
ssh-copy-id -i keyname servername
```

Chuck Nemeth

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