SSH Key Types Compared: RSA vs Ed25519 vs ECDSA
Which SSH key algorithm should you generate in 2026? Performance, security, and compatibility compared.
If you're still generating RSA 2048-bit SSH keys, it's time to upgrade. Ed25519 and ECDSA offer the same or better security with dramatically smaller keys and faster operations.
Side-by-side comparison
| Algorithm | Key size | Security level | Key gen | Signing speed | Compatibility |
|---|---|---|---|---|---|
| RSA 2048 | 2048 bit | ~112 bits | Slow | Fast | Universal |
| RSA 4096 | 4096 bit | ~152 bits | Very slow | Slower | Universal |
| ECDSA P-256 | 256 bit | ~128 bits | Fast | Very fast | OpenSSH 5.7+ |
| ECDSA P-384 | 384 bit | ~192 bits | Fast | Fast | OpenSSH 5.7+ |
| Ed25519 | 256 bit | ~128 bits | Instant | Instant | OpenSSH 6.5+ |
A 256-bit Ed25519 key provides the same security level as a 3072-bit RSA key — in 68 bytes instead of 2,500+.
Ed25519: the recommended default
Ed25519 (EdDSA over Curve25519) is the best choice for almost everyone in 2026:
- Tiny keys — 68 bytes (public) and 80 bytes (private). No more 4KB
authorized_keysfiles. - Instant key generation — useful when you need per-service or per-session keys.
- No NIST curves — Ed25519 was designed independently, avoiding the trust concerns around NIST-recommended curves.
- Supported everywhere — OpenSSH 6.5+ (released 2014), GitHub, GitLab, AWS, all major OSes.
ssh-keygen -t ed25519 -C "[email protected]"ECDSA: the fallback
If you must use a NIST curve (some enterprise SSH servers only accept ECDSA), P-256 is the sweet spot:
ssh-keygen -t ecdsa -b 256 -C "[email protected]"Avoid P-521 — it's slower with no practical security benefit over Ed25519.
RSA: only for legacy
RSA remains universally compatible. If you're connecting to old servers or embedded devices running ancient SSH versions, RSA 4096 is your only option:
ssh-keygen -t rsa -b 4096 -C "[email protected]"Never generate RSA keys shorter than 4096 bits. RSA 2048 is below the 128-bit security threshold and deprecated by NIST.
Converting between formats
You may need to convert keys between PEM, OpenSSH, and JWK formats when working across ecosystems:
# PEM to OpenSSH
ssh-keygen -i -f key.pem > key.pub
# OpenSSH to PEM
ssh-keygen -e -m pem -f key.pub > key_pem.pubThe Key Toolkit generates RSA, EC (P-256/P-384/P-521), and Ed25519 key pairs, inspects existing keys, extracts public keys, computes fingerprints, and converts between PEM, DER, JWK, and OpenSSH formats — all in your browser.