/** @throws HDDerivationException if privKeyBytes is invalid (0 or >= n). */
public static DeterministicKey createMasterPrivKeyFromBytes(byte[] privKeyBytes, byte[] chainCode)
throws HDDerivationException {
BigInteger privateKeyFieldElt = HDUtils.toBigInteger(privKeyBytes);
assertNonZero(privateKeyFieldElt, "Generated master key is invalid.");
assertLessThanN(privateKeyFieldElt, "Generated master key is invalid.");
return new DeterministicKey(
ImmutableList.<ChildNumber>of(), chainCode, null, privateKeyFieldElt, null);
}
/**
* @throws HDDerivationException if private derivation is attempted for a public-only parent key,
* or if the resulting derived key is invalid (eg. private key == 0).
*/
public static DeterministicKey deriveChildKey(DeterministicKey parent, ChildNumber childNumber)
throws HDDerivationException {
RawKeyBytes rawKey = deriveChildKeyBytes(parent, childNumber);
return new DeterministicKey(
HDUtils.append(parent.getChildNumberPath(), childNumber),
rawKey.chainCode,
parent.hasPrivate() ? null : HDUtils.getCurve().decodePoint(rawKey.keyBytes),
parent.hasPrivate() ? HDUtils.toBigInteger(rawKey.keyBytes) : null,
parent);
}
private static RawKeyBytes deriveChildKeyBytes(DeterministicKey parent, ChildNumber childNumber)
throws HDDerivationException {
byte[] parentPublicKey = HDUtils.getBytes(parent.getPubPoint());
assert parentPublicKey.length == 33 : parentPublicKey.length;
ByteBuffer data = ByteBuffer.allocate(37);
if (childNumber.isPrivateDerivation()) {
data.put(parent.getPrivKeyBytes33());
} else {
data.put(parentPublicKey);
}
data.putInt(childNumber.getI());
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 = HDUtils.toBigInteger(il);
assertLessThanN(ilInt, "Illegal derived key: I_L >= n");
byte[] keyBytes;
final BigInteger privAsFieldElement = parent.getPrivAsFieldElement();
if (privAsFieldElement != null) {
BigInteger ki = privAsFieldElement.add(ilInt).mod(HDUtils.getEcParams().getN());
assertNonZero(ki, "Illegal derived key: derived private key equals 0.");
keyBytes = ki.toByteArray();
} else {
checkArgument(
!childNumber.isPrivateDerivation(),
"Can't use private derivation with public keys only.");
ECPoint Ki = HDUtils.getEcParams().getG().multiply(ilInt).add(parent.getPubPoint());
checkArgument(
!Ki.equals(HDUtils.getCurve().getInfinity()),
"Illegal derived key: derived public key equals infinity.");
keyBytes = HDUtils.toCompressed(Ki.getEncoded());
}
return new RawKeyBytes(keyBytes, chainCode);
}
