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); }