normalize method
'normalize' this signature by converting its s to lower-s form if necessary This is required to validate this signature with some libraries such as libsecp256k1 which enforce lower-s form for all signatures to combat ecdsa signature malleability
Returns this if the signature was already normalized, or a copy if it is changed.
Implementation
ECSignature normalize(ECDomainParameters curveParams) {
if (isNormalized(curveParams)) {
return this;
}
return ECSignature(r, curveParams.n - s);
}