/// <summary>
/// Recreates the private key of the parent from the private key of the child
/// combinated with the public key of the parent (hardened children cannot be
/// used to recreate the parent).
/// </summary>
public ExtKey GetParentExtKey(ExtPubKey parent)
{
if (parent == null)
{
throw new ArgumentNullException("parent");
}
if (this.Depth == 0)
{
throw new InvalidOperationException("This ExtKey is the root key of the HD tree");
}
if (this.IsHardened)
{
throw new InvalidOperationException("This private key is hardened, so you can't get its parent");
}
var expectedFingerPrint = parent.CalculateChildFingerprint();
if (parent.Depth != this.Depth - 1 || !expectedFingerPrint.SequenceEqual(this.vchFingerprint))
{
throw new ArgumentException("The parent ExtPubKey is not the immediate parent of this ExtKey",
"parent");
}
byte[] l = null;
var ll = new byte[32];
var lr = new byte[32];
var pubKey = parent.PubKey.ToBytes();
l = Hashes.BIP32Hash(parent.vchChainCode, this.nChild, pubKey[0], pubKey.SafeSubarray(1));
Array.Copy(l, ll, 32);
Array.Copy(l, 32, lr, 0, 32);
var ccChild = lr;
var parse256LL = new BigInteger(1, ll);
var N = ECKey.CURVE.N;
if (!ccChild.SequenceEqual(this.vchChainCode))
{
throw new InvalidOperationException(
"The derived chain code of the parent is not equal to this child chain code");
}
var keyBytes = this.PrivateKey.ToBytes();
var key = new BigInteger(1, keyBytes);
var kPar = key.Add(parse256LL.Negate()).Mod(N);
var keyParentBytes = kPar.ToByteArrayUnsigned();
if (keyParentBytes.Length < 32)
{
keyParentBytes = new byte[32 - keyParentBytes.Length].Concat(keyParentBytes).ToArray();
}
var parentExtKey = new ExtKey
{
vchChainCode = parent.vchChainCode,
nDepth = parent.Depth,
vchFingerprint = parent.Fingerprint,
nChild = parent.nChild,
key = new Key(keyParentBytes)
};
return(parentExtKey);
}
