SSH keys all do the same basic job, letting a computer prove its identity without a password. But the type matters, different algorithms mean different security and compatibility tradeoffs.

Setting up SSH today, you’ll mostly run into Ed25519 and RSA. ECDSA’s still around too. DSA? Leave it in the history book.

Ed25519 Is the Modern Favorite

Become the go-to for a lot of new setups. Based on elliptic curve cryptography, strong security without needing a huge key, and quick to create and use too.

Private key file’s small, authentication feels almost instant, you stop noticing it after a while, which is exactly what a good SSH setup should feel like.

Why People Pick Ed25519

Combines strong security with practical performance, OpenSSH supports it widely, modern Linux distros handle it without fuss. Small key size keeps things neat moving keys between systems. Fast authentication, no sitting around waiting. Solid modern default, especially for a new server that isn’t stuck supporting ancient software.

RSA Still Has Plenty of Life Left

The old reliable option, used with SSH for years, you’ll find it on plenty of existing servers and dev machines.

Key size matters here, commonly 2048 bits or more, sometimes 3072 or 4096. Larger keys take more work to process, but compatibility’s where RSA earns its keep. Managing an older environment, RSA’s often the practical choice since older implementations understand it more reliably.

ECDSA and the Older Key Types

ECDSA uses elliptic curve crypto too, but it’s rarely the first pick for a fresh setup, Ed25519’s simpler to recommend with better modern support.

DSA, also called DSS, is disabled by default in modern OpenSSH since it’s considered obsolete. Find an old DSA key on a server? Replace it, don’t treat it as some clever trick.

Which SSH Key Should You Use?

New setup, use Ed25519 unless there’s a specific compatibility reason not to. Compact, fast, widely supported, no unnecessary complexity.

RSA makes sense for older systems that don’t properly support Ed25519. ECDSA has its place, but little reason to pick it just because it’s available.

And the algorithm’s not the whole story. Protect the private key, use a passphrase, keep old keys out of systems you no longer control. SSH should feel boring once it’s set up right.