ECDSA Sign / Verify
Sign and verify messages with elliptic-curve cryptography — small keys, strong security.
Never paste a real production private key into a website. This page runs entirely in your browser, but for real secrets the safest place is your own machine. Use the sample keys to learn and test.
● 🔒 Your data is processed locally in your browser with the Web Crypto API and is never uploaded to our servers.
How it works
ECDSA gives the same security as RSA with much smaller keys: a 256-bit P-256 key is about as strong as 3072-bit RSA. The hash matches the curve (SHA-256 for P-256, SHA-384 for P-384, SHA-512 for P-521), as in JWT's ES256/384/512. Browsers produce raw signatures (r and s concatenated); OpenSSL and most languages expect ASN.1 DER — the tool converts between them.