DEV Community

楊東霖
楊東霖

Posted on • Originally published at devplaybook.cc

SSH Key Generator Guide: Generate RSA and Ed25519 Keys for Secure Access

#webdev #programming #productivity #devtools

SSH Key Generator Guide: Generate RSA and Ed25519 Keys for Secure Access

SSH keys are the standard way to authenticate with remote servers, GitHub, and CI/CD systems — without passwords. This guide covers how to generate them correctly, choose the right key type, and set them up securely.

Generate RSA Keys Online →

SSH Key Pair Basics

SSH authentication uses asymmetric cryptography:

  • Private key — stays on your machine. Never share it.
  • Public key — shared with servers, GitHub, and services you want to access.

When you connect, the server challenges you with a random message encrypted with your public key. Only your private key can decrypt it — proving your identity without sending a password.

Key Types: RSA vs Ed25519 vs ECDSA

Type Recommended Size Speed Security Compatibility
Ed25519 Fixed (256-bit) Fastest Excellent Modern systems (2014+)
RSA 4096-bit Slower Good Maximum compatibility
ECDSA 521-bit Fast Good Most modern systems

Use Ed25519 if you're setting up new keys today — it's faster, shorter, and has better security properties than RSA.

Use RSA (4096-bit) if you need to connect to older systems that don't support Ed25519.

Generate SSH Keys on Linux/macOS

Ed25519 (recommended) 

ssh-keygen -t ed25519 -C "your@email.com"
Enter fullscreen mode Exit fullscreen mode

Output:

Generating public/private ed25519 key pair.
Enter file in which to save the key (/home/user/.ssh/id_ed25519):
Enter passphrase (empty for no passphrase): [choose a strong passphrase]
Enter same passphrase again:
Your identification has been saved in /home/user/.ssh/id_ed25519
Your public key has been saved in /home/user/.ssh/id_ed25519.pub
Enter fullscreen mode Exit fullscreen mode

RSA 4096-bit 

ssh-keygen -t rsa -b 4096 -C "your@email.com"
Enter fullscreen mode Exit fullscreen mode

Named keys (multiple identities) 

# For work GitHub account
ssh-keygen -t ed25519 -f ~/.ssh/id_ed25519_work -C "work@company.com"

# For personal server
ssh-keygen -t ed25519 -f ~/.ssh/id_ed25519_vps -C "personal-vps"
Enter fullscreen mode Exit fullscreen mode

Generate SSH Keys on Windows

Using Git Bash or WSL

Same commands as Linux:

ssh-keygen -t ed25519 -C "your@email.com"
Enter fullscreen mode Exit fullscreen mode

Using PowerShell (Windows 10+) 

# OpenSSH is built in on Windows 10 1809+
ssh-keygen -t ed25519 -C "your@email.com"
# Keys saved to C:\Users\YourName\.ssh\
Enter fullscreen mode Exit fullscreen mode

View Your Public Key 

# Ed25519
cat ~/.ssh/id_ed25519.pub

# RSA
cat ~/.ssh/id_rsa.pub

# Output looks like:
# ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAA... your@email.com
Enter fullscreen mode Exit fullscreen mode

The entire single line starting with ssh-ed25519 or ssh-rsa is your public key. This is what you paste into GitHub, server authorized_keys, or CI/CD settings.

Add Public Key to GitHub

  1. Copy your public key: 
cat ~/.ssh/id_ed25519.pub | pbcopy  # macOS
cat ~/.ssh/id_ed25519.pub | xclip -selection clipboard  # Linux
Enter fullscreen mode Exit fullscreen mode
  1. GitHub → Settings → SSH and GPG keys → New SSH key
  2. Paste the public key, give it a name (e.g., "MacBook Pro 2026")
  3. Test the connection: 
ssh -T git@github.com
# Hi username! You've successfully authenticated.
Enter fullscreen mode Exit fullscreen mode

Add Public Key to a Server 

# Append your public key to the server's authorized_keys
ssh-copy-id -i ~/.ssh/id_ed25519.pub user@server-ip

# Or manually:
cat ~/.ssh/id_ed25519.pub | ssh user@server-ip "mkdir -p ~/.ssh && cat >> ~/.ssh/authorized_keys && chmod 600 ~/.ssh/authorized_keys"
Enter fullscreen mode Exit fullscreen mode

SSH Config File: Managing Multiple Keys

Create ~/.ssh/config to set per-host options:

# Personal GitHub
Host github.com
  HostName github.com
  User git
  IdentityFile ~/.ssh/id_ed25519

# Work GitHub (separate account)
Host github-work
  HostName github.com
  User git
  IdentityFile ~/.ssh/id_ed25519_work

# Production server
Host prod
  HostName 203.0.113.10
  User deploy
  IdentityFile ~/.ssh/id_ed25519_vps
  Port 2222
Enter fullscreen mode Exit fullscreen mode

Usage with config:

# Clone work repo using work identity
git clone git@github-work:company/repo.git

# Connect to prod using alias
ssh prod
Enter fullscreen mode Exit fullscreen mode

SSH Key Security Best Practices

Always use a passphrase. A passphrase encrypts your private key on disk. Even if someone steals your key file, they can't use it without the passphrase.

# Add passphrase to existing key
ssh-keygen -p -f ~/.ssh/id_ed25519
Enter fullscreen mode Exit fullscreen mode

Use ssh-agent to avoid typing the passphrase repeatedly:

eval "$(ssh-agent -s)"
ssh-add ~/.ssh/id_ed25519
# Enter passphrase once — agent remembers it for the session
Enter fullscreen mode Exit fullscreen mode

File permissions matter:

chmod 700 ~/.ssh
chmod 600 ~/.ssh/id_ed25519
chmod 644 ~/.ssh/id_ed25519.pub
chmod 600 ~/.ssh/authorized_keys
chmod 600 ~/.ssh/config
Enter fullscreen mode Exit fullscreen mode

Rotate keys regularly. Treat SSH keys like passwords: rotate annually or when someone who had access leaves.

Separate keys for separate purposes. Don't use the same key for your personal GitHub, your work server, and your CI/CD pipeline.

SSH Keys in CI/CD

For GitHub Actions, CircleCI, and other CI systems:

# GitHub Actions example
# Store private key as a secret: SSH_PRIVATE_KEY
jobs:
  deploy:
    runs-on: ubuntu-latest
    steps:
      - name: Setup SSH
        run: |
          mkdir -p ~/.ssh
          echo "${{ secrets.SSH_PRIVATE_KEY }}" > ~/.ssh/id_ed25519
          chmod 600 ~/.ssh/id_ed25519
          ssh-keyscan -H your-server.com >> ~/.ssh/known_hosts

      - name: Deploy
        run: ssh deploy@your-server.com 'cd /app && git pull && npm run build'
Enter fullscreen mode Exit fullscreen mode

Generate a dedicated deployment key — not your personal key:

ssh-keygen -t ed25519 -f deploy_key -N "" -C "ci-deploy"
# -N "" creates a key with no passphrase (required for automated scripts)
cat deploy_key.pub  # Add to server's authorized_keys
cat deploy_key      # Store as CI secret
Enter fullscreen mode Exit fullscreen mode

Troubleshooting

Permission denied (publickey):

# Debug connection
ssh -v git@github.com

# Check which key is being offered
ssh-add -l

# Make sure the key is loaded
ssh-add ~/.ssh/id_ed25519
Enter fullscreen mode Exit fullscreen mode

Wrong key being used:

# Force a specific key
ssh -i ~/.ssh/id_ed25519_work git@github.com
Enter fullscreen mode Exit fullscreen mode

Server not accepting key:

# Check authorized_keys on server
cat ~/.ssh/authorized_keys  # Make sure your public key is in here
ls -la ~/.ssh/  # Check permissions
Enter fullscreen mode Exit fullscreen mode

Conclusion

Ed25519 is the recommended key type for all new SSH keys today. Generate it with ssh-keygen -t ed25519, always use a passphrase, and add it to ssh-agent for convenience. Use ~/.ssh/config to manage multiple keys across different servers and accounts.

Generate RSA Key Pairs Online →

Level Up Your Dev Workflow

Found this useful? Explore DevPlaybook — cheat sheets, tool comparisons, and hands-on guides for modern developers.

🛒 Get the DevToolkit Starter Kit on Gumroad — 40+ browser-based dev tools, source code + deployment guide included.

Top comments (0)