ECDSA Sign
Sign a message with an ECDSA private key.
Sign a message with an ECDSA private key. Free, offline, runs entirely in your browser. Read more Show less
What is an ECDSA signature?
An ECDSA signature proves that a message was signed by the holder of an EC private key. Signatures are compact (around 70-140 bytes depending on curve) and verification is fast.
How to use
Paste an ECDSA private key in PEM format. Type or paste the message. Choose the hash. Click Sign.
Signature encoding can be Base64 or Hex. Use the same encoding when verifying.
FAQ
Is my private key sent anywhere?
No. Signing runs entirely in your browser.
Which hash should I use?
Match the curve: P-256 with SHA-256, P-384 with SHA-384, P-521 with SHA-512. Other combinations work but are less standard.
Is the signature deterministic?
Web Crypto uses a random nonce, so signing the same message twice produces different signatures. Both verify correctly.
How to verify
ECDSA signatures in Web Crypto use the raw (r, s) format defined in IEEE P1363, not the DER-encoded ASN.1 format that openssl produces by default. To verify with openssl, convert to DER first, or use a tool that accepts raw signatures.
The easiest verification is to paste the result into the ECDSA Verify tool with the matching public key.