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SSH keys use strong encryption

Time to fix

< 1m

What

Strong SSH key encryption with adequate key sizes is required to prevent brute-force attacks on your private keys. Weak keys can be compromised relatively quickly with modern computing power.

Why key strength matters

Attackers with access to your private key file will attempt to crack it through brute force or cryptographic attacks. Strong encryption algorithms and sufficient key lengths make this process computationally infeasible.

Check your SSH key strength

Check the algorithm and key size of your existing keys:

ssh-keygen -l -f ~/.ssh/id_rsa
ssh-keygen -l -f ~/.ssh/id_ed25519
ssh-keygen -l -f ~/.ssh/id_ecdsa

The output shows the key size (first number) and algorithm type.

Recommended key standards

Use these minimum key sizes and algorithms:

✅ Recommended (Strong)
  • Ed25519: 256 bits (modern, fast, secure)
  • RSA: 4096 bits minimum
  • ECDSA: 521 bits (P-521 curve)
⚠️ Acceptable (Minimum)
  • RSA: 2048 bits (legacy systems only)
  • ECDSA: 384 bits (P-384 curve)
❌ Weak (Replace immediately)
  • RSA: Less than 2048 bits
  • DSA: Any size (deprecated algorithm)
  • ECDSA: 256 bits or smaller

Generate new strong SSH keys

Create new keys with strong encryption:

Ed25519 (Recommended)
ssh-keygen -t ed25519 -C "[email protected]"

Modern, fast, and cryptographically secure.

RSA 4096-bit
ssh-keygen -t rsa -b 4096 -C "[email protected]"

Use when Ed25519 is not supported by target systems.

ECDSA P-521
ssh-keygen -t ecdsa -b 521 -C "[email protected]"

Alternative to RSA for older systems that don't support Ed25519.

Verify your keys online

Check the strength of keys you use on public services:

  • Visit aremykeyssafe.com
  • Enter your username from GitHub, GitLab, or other services
  • Review the security report for your public keys

Replace weak keys

If you have weak keys, generate new ones and update all systems:

  1. Generate a new strong key using the commands above
  2. Add the new public key to all servers and services
  3. Test SSH access with the new key
  4. Remove the old weak key from servers
  5. Delete the old weak key files from your system
Migration Strategy

When replacing weak keys, gradually migrate rather than doing everything at once. Start with the most critical systems and work your way down to ensure you don't lock yourself out.

Future-Proofing

Choose Ed25519 for new keys whenever possible. It's the most modern algorithm with excellent security properties and performance characteristics.

Key Management

Keep track of where each key is used and regularly audit your SSH keys. Remove unused keys and rotate them periodically as part of good security hygiene.