I'm using c# NBitcoin to generate master key at an offline server

ExtKey privateKey = new ExtKey("[My seed]");
ExtPubKey pubKey = privateKey.Neuter();

I will need to give the online server the master public key, and it can generate as many addresses it needs, my questions are:

How do I pass the master public key (pubKey) to this code in the online server ?

BitcoinAddress address1 = **pubKey**.Derive([some client data]).PubKey.GetAddress(Network.Main);

What is the best practice to listen for a payment received on this new address ? I'm working with web requests to http://btc.blockr.io/api/v1/address/unconfirmed/[address1]
My language is c# server side.

2 Answers 2


when you are doing

BitcoinAddress address1 = **pubKey**.Derive([some client data]).PubKey.GetAddress(Network.Main);

You are getting the bitcoin address, but not the master public key. (ExtPubKey) A HD pub key have more information than just the pubkey.

The correct code is

string wifStr = **pubkey**.Derive([some client data]).ToString(Network.Main)

Then you can reload it

ExtPubKey key = ExtPubKey.Parse(wifStr)

In fact, the string format of an ExtPubKey have the Network to which it belong, that's why you also have the type "BitcoinExtKey" which represent in object oriented form both : the ExtPubKey AND the Network. If you need it :

BitcoinExtPubKey wif = **pubkey**.GetWif(Network.Main)

Take a look at my book, there is other code samples around HD keys.

Concerning the best practices, there is no silver bullet right now. I created an API called RapidBase which permit you to create wallet and add addresses to monitor in this wallet. (You can find it on github)

You can try it if you want, but it is very unstable for now (API wise), so expect things to change in the future. If you are using blockr, I think your best bet is to request each addresses as you are doing.

If you are using bitcoinq RPC, you can add address, but it takes time since bitcoin core will rescan the blockchain for fetching the relevant transactions each time.

I might be wrong, but for now there is no easy to use solution, exception rapidbase I developed, that is not very stable for now.

  • 1
    But he's not interested in the chaincode - he doesn't need the extended child key. What he needs is a way to monitor an address.
    – Nick ODell
    Commented Apr 3, 2015 at 16:15
  • Well, this is a two part question "How do I pass the master public key (pubKey) to this code in the online server ?" This is a response to this one. I'm editing the response for his second question. Commented Apr 3, 2015 at 16:18
  • Ah, I see. I didn't see that first question.
    – Nick ODell
    Commented Apr 3, 2015 at 16:19
  • didn't see the second one :D Commented Apr 3, 2015 at 16:24
  • 1
    you have a wif version of both : ExtKey and ExtPubKey, if you have the ExtKey and want the ExtPubKey, just do extKey.Neuter().ToString(Network.Main) Commented Apr 3, 2015 at 22:31
////////////////1st offline SERVER//////////////////
//Create Master Private Key with a seed
ExtKey privateKey = new ExtKey("16236c2028fd2018eb7049825e6b4f0191de4dbff003579918de7b7348ff06ac");
//create master public key from this privateKey
ExtPubKey pubKey = privateKey.Neuter();
//save it's wifStr as key to the next server to use and generate all child keys 
string wifStr = pubKey.ToString(Network.Main);

////////////////2nd online SERVER//////////////////
ExtPubKey key = ExtPubKey.Parse(wifStr);
//The payment server receive an order, note the server does not need the private key to generate the address
uint orderID = 1001;
BitcoinAddress address = key.Derive(orderID).PubKey.GetAddress(Network.Main);

////////////////3rd admin SERVER//////////////////
//Now on the server that have access to the private key, you get the private key from the orderID
ExtKey mPrivateKey = new ExtKey("16236c2028fd2018eb7049825e6b4f0191de4dbff003579918de7b7348ff06ac");
Key key1 = mPrivateKey.Derive(orderID).Key;
BitcoinSecret secret = key1.GetBitcoinSecret(Network.Main);
Console.WriteLine(secret); //Print a nice secret key string
  • 1
    the code is right, except new ExtKey(string) does not exist. If you have the private ExtKey, use ExtKey.ToString(Network) / ExtKey.Parse(wif) Commented Apr 3, 2015 at 22:32

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