Signing a message with privateKey (elliptic p256)

Question

How do we sign a message with a givenPrivateKey in java with elliptic curve(p256)

Basically a java implementation of

let elliptic = new EC('p256')
const sig = elliptic.sign(msgHashHex, privateKey, null)

I dont want to generate new private/public key pair. My privateKey = 'abc'

Also please let me know if there is an online tool to play around with digital signatures.

Thanks a lot in advance.

Answer 1

PrivateKey privateKey = ; // your  EC p256 private key
byte[] msgHashHex = ; // byte array data

Signature signature = Signature.getInstance("ECDSA"); // or SHA256WithECDSA etc.
signature.initSign(privateKey);
signature.update(msgHashHex);   
byte[] result = signature.sign();