Master of Science thesis Fighting Spam

public CurrencyExchangeClient() throws Exception
{
CESCertificate = FileHandler.importCertificate(new
File(Config.CESCertificateName));
BLSCertificate = FileHandler.importCertificate(new
File(Config.BLSCertificateName));
}
/**
* Method to start a currencyExchange with the server
* @param username String
* @param password String
* @throws Exception An exception is thrown when the connection encounters problems
*/
public boolean logonToCurrencyServer(String username, String password) throws
Exception
{
StatusPacket pack = logon(username, password);
if(pack.ok)
{
this.username = username;
this.password = password;
}
else
throw new Exception(pack.message);
return pack.ok;
}
private StatusPacket logon(String username, String password) throws Exception
{
//If a valid session does not exist..create one.
checkSession();
}
//logon
serverSession.send(new LogonPacket(username, password));
StatusPacket responsePacket = (StatusPacket) serverSession.receive();
return responsePacket;
private void checkSession() throws Exception
{
if(serverSession == null || serverSession.closed)
{
createSession();
}
}
private void createSession() throws Exception
{
Debugger.debug(getClass(), 3, "Creating new session with the CES: " +
Config.CESAddress + ":" + Config.CESPort);
Socket socket = new Socket(InetAddress.getByName(Config.CESAddress),
Config.CESPort);
serverSession = new session(socket, false, (RSAPublicKey)
CESCertificate.getPublicKey(),true);
}
public Coin[] withdraw(double amount, Certificate certificate) throws Exception
{
Debugger.debug(getClass(), 3, "Withdrawing "+amount+"...");
int necessaryCoins = necessaryCoins(amount);
Coin[][] coins = generateCoins(necessaryCoins);
checkSession();
//Initialize blindingFactors and blind the coins
RSABlindingFactor[][] blindingFactors = new
RSABlindingFactor[coins.length][coins[0].length];
BlindedCoin[][] blindedCoins = new BlindedCoin[coins.length][coins[0].length];
for(int i = 0; i < coins.length; i++)
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