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Last updated: April 29, 2026
Asymmetric (public-key) crypto for digital signatures and key exchange.
Asymmetric (public-key) crypto for digital signatures and key exchange.
The choices
- RSA-2048 — minimum acceptable; phasing out for 4096 in regulated
- RSA-4096 — slow; use only when compatibility requires
- ECDSA P-256 — fast; smaller keys (256-bit ~ RSA-3072 strength)
- Ed25519 — modern; fast; safer-by-default than ECDSA
- X25519 — for ECDH key agreement
When to use which
| Use case | Recommended |
|---|---|
| TLS server cert | ECDSA P-256 or RSA-2048 |
| SSH host key | Ed25519 |
| SSH user key | Ed25519 |
| Code signing | RSA-2048+ (vendor mandates) |
| JWT signing | EdDSA (Ed25519) or ES256 |
| Key exchange | X25519 |
Implementation pitfalls
- RSA padding errors (always use OAEP for encryption, PSS for signing)
- ECDSA nonce reuse = private key extraction
- Don’t roll your own; use mature libraries
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