Proof of ownership as an authentication method

[2016.05.02] My name is Craig Wright and I am about to demonstrate a signing of a message with the public key that is associated with the first transaction ever done in Bitcoin.

var bitcoinPrivateKey = new BitcoinSecret("XXXXXXXXXXXXXXXXXXXXXXXXXX");
var message = "I am Craig Wright";
string signature = bitcoinPrivateKey.PrivateKey.SignMessage(message);
Console.WriteLine(signature); // IN5v9+3HGW1q71OqQ1boSZTm0/DCiMpI8E4JB1nD67TCbIVMRk/e3KrTT9GvOuu3NGN0w8R2lWOV2cxnBp+Of8c=

Was that so hard?

You may remember Craig Wright, who really wanted us to believe he is Satoshi Nakamoto. He had successfully convinced a handful of influential Bitcoin people and journalists with some social engineering. Fortunately digital signatures do not work that way. Let's quickly find on the Internet the first ever bitcoin address, associated with the genesis block: 1A1zP1eP5QGefi2DMPTfTL5SLmv7DivfNa and verify his claim:

var message = "I am Craig Wright";
var signature = "IN5v9+3HGW1q71OqQ1boSZTm0/DCiMpI8E4JB1nD67TCbIVMRk/e3KrTT9GvOuu3NGN0w8R2lWOV2cxnBp+Of8c=";
var address = new BitcoinPubKeyAddress("1A1zP1eP5QGefi2DMPTfTL5SLmv7DivfNa");
bool isCraigWrightSatoshi = address.VerifyMessage(message, signature);
Console.WriteLine("Is Craig Wright Satoshi? " + isCraigWrightSatoshi);

SPOILER ALERT! The bool will be false.

Here is how you prove you are the owner of an address without moving coins:

Address: 1KF8kUVHK42XzgcmJF4Lxz4wcL5WDL97PB Message: Nicolas Dorier Book Funding Address Signature: H1jiXPzun3rXi0N9v9R5fAWrfEae9WPmlL5DJBj1eTStSvpKdRR8Io6/uT9tGH/3OnzG6ym5yytuWoA9ahkC3dQ=

This constitutes proof that Nicolas Dorier owns the private key of the book. Exercise: Verify that Nicolas sensei is not lying!

Sidenote

Do you know how PGP works? Pretty similar, right? Maybe this can be the foundation of a more user friendly PGP alternative. Please build it on top of NBitcoin :-)