Smart contract for Ethereum's account owner verification using Cryptonomica.net notary verified OpenPGP public key

Verificator.sol

/*
Usage:

1. Account owner sends a request for verification, in this request he sends a fingerprint of his OpenPGP key stored on cryptonomica.net
2. This contracts sends back a string to sign
3. Accont owener signs this strign with his OpenPGP key and sends back to smartcontract.
4. Information about verification is public visible - who needs to check can download verified public key from cryptonomica.net and check if owner of stated Ehereum acconts is also known owner of verified OpenPGP key on cryptonomica.net

It's also possible to create a web-inerface using Cryptonomica's API like:

GET https://cryptonomica-server.appspot.com/_ah/api/pgpPublicKeyAPI/v1/getPGPPublicKeyByFingerprint?fingerprint=57A5FEE5A34D563B4B85ADF3CE369FD9E77173E5

(Authorization required)

*/

import "github.com/Arachnid/solidity-stringutils/strings.sol";

contract Verificator {

    string public creator;
    mapping (address => bytes32) public stringToSign;
    mapping (address => string) public signedString;
    mapping (address => string) public keyFingerprint;
    mapping (address => string) public urlToVerifyKey;
    string urlBase;

    function Verificator(){
        creator = "www.cryptonomica.net";
        urlBase = "https://cryptonomica.net/#/key/";
    }

    function getStringToSignWithKey(string _fingerprint) returns (bytes32) {

        keyFingerprint[msg.sender] = _fingerprint;
        urlToVerifyKey[msg.sender] = strings.concat(
                                        strings.toSlice(urlBase),
                                        strings.toSlice(_fingerprint)
                                    );

        var strToSign = sha3(
                msg.sender,
                block.blockhash(block.number),
                block.timestamp,
                block.blockhash(block.number - 250)
            );

        stringToSign[msg.sender] = strToSign;
        signedString[msg.sender] = "waiting to singed string";

        return stringToSign[msg.sender];
    }

    function uploadSignedString(string _signedString){

        signedString[msg.sender] = _signedString;
    }

}