Start with the destination requirement
Choose ECDSA when the receiving server, appliance, or policy explicitly requires it. P-256 usually offers the widest ECDSA compatibility. P-384 is a higher-security policy profile, while P-521 is best reserved for a named requirement. Ed25519 remains the simpler choice for a new identity when the destination supports it.
Compare ECDSA curves
| Curve | Choose it for | Guidance |
|---|---|---|
| P-256 | Most ECDSA SSH destinations | Broadest ECDSA compatibility |
| P-384 | A documented higher-security profile | Confirm both client and server support |
| P-521 | A specialized policy requirement | Use only when the destination names it |
Choose the private-key container
Use OpenSSH for current SSH clients, PKCS#8 for Java and general cryptographic tooling, or PuTTY PPK v3 for current PuTTY software. SEC1 EC PEM is available under Advanced formats for an EC-specific destination. PPK v2 remains an explicit legacy option. PKCS#1 is RSA-only and is never offered for ECDSA.
- Confirm the destination's algorithm, curve, and container requirements.
- Protect the private output with a passphrase unless a controlled automation process requires otherwise.
- Keep the original key until the converted copy has been tested.
- Compare the SHA-256 SSH fingerprint before replacing any file.
The Local Dev Kit generator, converter, and Format Doctor run in the browser. Key material and passphrases are not sent to the application server.
ECDSA SSH key questions
Which ECDSA curve should I choose for SSH?
Use the curve required by the destination. When ECDSA is required and no curve is specified, P-256 usually has the broadest compatibility. P-384 and P-521 are useful when a documented policy names them.
Can I convert an ECDSA key to Ed25519 or RSA?
No. A container conversion keeps the same ECDSA curve and public fingerprint. Use Generate to create a separate SSH identity when the destination requires another algorithm.
What is the difference between PKCS#8 and SEC1 EC PEM?
PKCS#8 is an algorithm-neutral private-key container used by Java and general cryptographic tooling. SEC1 EC PEM is an EC-specific representation used by some OpenSSL and older integration workflows.
Does changing an ECDSA key container change its fingerprint?
No. OpenSSH, PKCS#8, SEC1, and PuTTY PPK can contain the same ECDSA scalar and public point. A safe conversion derives and compares the SHA-256 SSH fingerprint before returning output.