Question 1

Which SSH key type should I use in 2024?

Accepted Answer

Ed25519 is the recommended choice: small keys (256-bit), fast, resistant to timing attacks, and supported by all modern SSH servers (OpenSSH 6.5+, 2014). ECDSA-256 is a reasonable alternative. RSA-4096 is still secure but slower and produces larger keys. Avoid RSA-1024 and RSA-2048 for new keys — RSA-1024 is considered broken; RSA-2048 may become inadequate by 2030. Never use DSA: it was deprecated in OpenSSH 7.0.

Question 2

What is an SSH key fingerprint?

Accepted Answer

A fingerprint is a short hash of the public key, used to identify it without displaying the full key. When you first SSH to a server, you see the host key fingerprint and are asked to verify it. SHA256 fingerprints (the modern default) look like SHA256:base64string. MD5 fingerprints look like colon-separated hex. Always verify fingerprints out-of-band to prevent man-in-the-middle attacks.

Question 3

Is it safe to share my SSH public key?

Accepted Answer

Yes. The public key (the .pub file) is meant to be shared — it is placed in ~/.ssh/authorized_keys on servers you want to access. The private key (id_rsa, id_ed25519, etc.) must never be shared. The security of SSH depends on keeping the private key private. If you suspect your private key is compromised, revoke the public key from all authorized_keys files immediately and generate a new pair.

Question 4

What is a passphrase on an SSH key?

Accepted Answer

A passphrase encrypts your private key file on disk. Without a passphrase, anyone who obtains the file can use it. With a passphrase, they also need to know the passphrase. Use ssh-agent or a hardware key (YubiKey) to avoid typing the passphrase repeatedly. Always protect private keys with a passphrase, especially on shared machines or laptops.

Type	Key size	Security	Notes
Ed25519	256-bit	✅ Excellent	Recommended. Fast, small, timing-attack resistant. OpenSSH 6.5+ (2014).
ECDSA-256	256-bit	✅ Good	Elliptic curve — good for constrained environments. Slightly weaker than Ed25519.
RSA-4096	4096-bit	✅ Good	Large keys, slower ops. Still widely compatible. Fine for legacy systems.
RSA-2048	2048-bit	⚠️ Acceptable	May become inadequate by 2030. Upgrade to 4096 or Ed25519 for new keys.
RSA-1024	1024-bit	❌ Broken	Factored in practice. Do not use — rejected by many servers.
DSA	1024-bit	❌ Deprecated	Removed in OpenSSH 7.0. Avoid entirely.

SSH Key Info

SSH key type comparison

Frequently asked questions

Related security tools

Inspect your SSH key security