# Using SSH Keys Instead of Passwords

Using SSH Keys Instead of Passwords – Server administration and Linux knowledge from NexoraHost.

This guide shows you why SSH keys are more secure and convenient than passwords and how to set them up. With an SSH key, you can log in without a password while protecting your server from brute-force attacks.

**Note:** The complete guide to SSH connections can be found in the article "SSH Connection and Key Authentication" in the left navigation.

## Why SSH Keys?

    
        
        Password
        SSH Key
    

    
        **Security**
        Can be guessed or stolen
        Practically impossible to crack (2^256 possibilities)
    

    
        **Brute-force protection**
        Attackers can try unlimited times
        No access possible without private key
    

    
        **Convenience**
        Enter password every time
        Set up once, never enter a password again
    

    
        **Automation**
        Password in script = security risk
        Perfect for scripts and cronjobs
    

## Step 1: Create a Key Pair

Run this command on **your local computer** – not on the server:

`ssh-keygen -t ed25519 -C "your-email@example.com"`

You'll be asked:

    - **Save location:** Press Enter for the default path (`~/.ssh/id_ed25519`)
- **Passphrase:** An additional password for the key (optional, but recommended)
- **Repeat passphrase:** Enter the same password again

After creation you have two files:

    - **id_ed25519** – Your private key (secret, never share!)
- **id_ed25519.pub** – Your public key (goes on the server)

## Step 2: Copy the Public Key to the Server

### Method A: Using ssh-copy-id (recommended)

`ssh-copy-id root@your-server-ip`
Enter your server password once. The key is transferred automatically.

### Method B: Manual Copy

`# On your local PC: Display public key
cat ~/.ssh/id_ed25519.pub

# On the server: Paste key into authorized_keys
ssh root@your-server-ip
mkdir -p ~/.ssh
echo "paste-your-copied-key-here" >> ~/.ssh/authorized_keys
chmod 600 ~/.ssh/authorized_keys
exit`

## Step 3: Test Key Login

`ssh root@your-server-ip`
If you set a passphrase, you'll be asked for it. Otherwise you're logged in immediately – without a password.

## Step 4: Disable Password Login (Recommended)

Once key login works, you should disable password login:

`sudo nano /etc/ssh/sshd_config`
Find and change the following lines:

`PasswordAuthentication no
ChallengeResponseAuthentication no
UsePAM no`
Restart the SSH service:

`sudo systemctl restart sshd`

**Important:** Test the key login beforehand in a second terminal window. If the key doesn't work and password login is disabled, you won't be able to access the server.

## SSH Keys on Windows with PuTTY

    - Open **PuTTYgen**
- Select **Ed25519** as key type and click **Generate**
- Move the mouse over the empty area to generate random data
- Save the private key (`.ppk` file) and copy the public key
- Add the public key on the server in `~/.ssh/authorized_keys`
- In PuTTY under **Connection → SSH → Auth** select the private key

## SSH Config File for Multiple Servers

Create `~/.ssh/config` on your local machine:

`Host my-server
    HostName 123.123.123.123
    User root
    IdentityFile ~/.ssh/id_ed25519

Host gameserver
    HostName 456.456.456.456
    User steam
    IdentityFile ~/.ssh/id_ed25519`
Then simply use `ssh my-server` to connect – without IP and username.

## Common Problems

**"Permission denied (publickey)":**

    - Was the public key correctly inserted in `authorized_keys`?
- Are the permissions correct? `chmod 700 ~/.ssh && chmod 600 ~/.ssh/authorized_keys`
- Is the private key on your local machine in the `~/.ssh/` folder?

**"Too many authentication failures":**

    - Too many keys in the `~/.ssh/` folder. Connect with a specific key:
        `ssh -i ~/.ssh/id_ed25519 root@server-ip`
    

*The complete guide to SSH connections with more details can be found in the article "SSH Connection and Key Authentication" in the left navigation.*