private static RawKeyBytes deriveChildKeyBytesFromPublic(
DeterministicKey parent, ChildNumber childNumber) throws HDDerivationException {
checkArgument(!childNumber.isHardened(), "Can't use private derivation with public keys only.");
byte[] parentPublicKey = ECKey.compressPoint(parent.getPubKeyPoint()).getEncoded();
assert parentPublicKey.length == 33 : parentPublicKey.length;
ByteBuffer data = ByteBuffer.allocate(37);
data.put(parentPublicKey);
data.putInt(childNumber.i());
byte[] i = HDUtils.hmacSha512(parent.getChainCode(), data.array());
assert i.length == 64 : i.length;
byte[] il = Arrays.copyOfRange(i, 0, 32);
byte[] chainCode = Arrays.copyOfRange(i, 32, 64);
BigInteger ilInt = new BigInteger(1, il);
assertLessThanN(ilInt, "Illegal derived key: I_L >= n");
ECPoint Ki = ECKey.CURVE.getG().multiply(ilInt).add(parent.getPubKeyPoint());
assertNonInfinity(Ki, "Illegal derived key: derived public key equals infinity.");
return new RawKeyBytes(Ki.getEncoded(true), chainCode);
}
private static RawKeyBytes deriveChildKeyBytesFromPrivate(
DeterministicKey parent, ChildNumber childNumber) throws HDDerivationException {
checkArgument(parent.hasPrivKey(), "Parent key must have private key bytes for this method.");
byte[] parentPublicKey = ECKey.compressPoint(parent.getPubKeyPoint()).getEncoded();
assert parentPublicKey.length == 33 : parentPublicKey.length;
ByteBuffer data = ByteBuffer.allocate(37);
if (childNumber.isHardened()) {
data.put(parent.getPrivKeyBytes33());
} else {
data.put(parentPublicKey);
}
data.putInt(childNumber.i());
byte[] i = HDUtils.hmacSha512(parent.getChainCode(), data.array());
assert i.length == 64 : i.length;
byte[] il = Arrays.copyOfRange(i, 0, 32);
byte[] chainCode = Arrays.copyOfRange(i, 32, 64);
BigInteger ilInt = new BigInteger(1, il);
assertLessThanN(ilInt, "Illegal derived key: I_L >= n");
final BigInteger priv = parent.getPrivKey();
BigInteger ki = priv.add(ilInt).mod(ECKey.CURVE.getN());
assertNonZero(ki, "Illegal derived key: derived private key equals 0.");
return new RawKeyBytes(ki.toByteArray(), chainCode);
}
