org.fisco.bcos.web3j.crypto.ECDSASignature Maven / Gradle / Ivy
package org.fisco.bcos.web3j.crypto;
import java.math.BigInteger;
/**
* An ECDSA Signature.
*/
public class ECDSASignature {
public final BigInteger r;
public final BigInteger s;
public ECDSASignature(BigInteger r, BigInteger s) {
this.r = r;
this.s = s;
}
/**
* @return true if the S component is "low", that means it is below
* {@link Sign#HALF_CURVE_ORDER}. See
*
* BIP62.
*/
public boolean isCanonical() {
return s.compareTo(Sign.HALF_CURVE_ORDER) <= 0;
}
/**
* Will automatically adjust the S component to be less than or equal to half the curve
* order, if necessary. This is required because for every signature (r,s) the signature
* (r, -s (mod N)) is a valid signature of the same message. However, we dislike the
* ability to modify the bits of a Bitcoin transaction after it's been signed, as that
* violates various assumed invariants. Thus in future only one of those forms will be
* considered legal and the other will be banned.
*
* @return the signature in a canonicalised form.
*/
public ECDSASignature toCanonicalised() {
if (!isCanonical()) {
// The order of the curve is the number of valid points that exist on that curve.
// If S is in the upper half of the number of valid points, then bring it back to
// the lower half. Otherwise, imagine that
// N = 10
// s = 8, so (-8 % 10 == 2) thus both (r, 8) and (r, 2) are valid solutions.
// 10 - 8 == 2, giving us always the latter solution, which is canonical.
return new ECDSASignature(r, Sign.CURVE.getN().subtract(s));
} else {
return this;
}
}
}