private static double GetSolveAttemptsPerSecond(byte[] payload, EstimationAccuracy accuracy)
{
CashPack pack = Packer.Pack(payload, (ushort)(payload.Length * 8));
Stopwatch watch = new Stopwatch();
int decrypts = 0;
watch.Start();
byte[] currentKey = new byte[pack.Key.Length];
Array.Copy(pack.Key, 0, currentKey, 0, pack.Key.Length);
byte[] solveWorkspace = new byte[pack.Payload.Length];
while (watch.ElapsedMilliseconds < ((uint)accuracy * 1000))
{
for (int i = 0; i < pack.Payload.Length; i++)
{
solveWorkspace[i] = (byte)(pack.Payload[i] ^ currentKey[i]);
}
// IMPORTANT: Use HMAC instead of Checksum
// This prevents you to do attacks where you can correlate known payloads
// And a CashPack without ever solving it.
using (HMACSHA512 sha = new HMACSHA512(currentKey))
{
byte[] hash = sha.ComputeHash(solveWorkspace);
for (int i = 0; i < pack.Hash.Length; i++)
{
if (pack.Hash[i] != hash[i])
{
break;
}
}
}
// Increment key
ulong keyAsNumber = BitHelper.KeyToNumber(currentKey, pack.BitDifficulty);
BitHelper.SetLastBitNumberBytes(currentKey, keyAsNumber + 1, pack.BitDifficulty);
decrypts++;
}
watch.Stop();
return(decrypts / (watch.ElapsedMilliseconds / 1000d));
}
/// <summary>
/// Solves a CashPack in a single go. Only recommended to be used for very easy CashPacks that takes no more than a few minutes.
/// </summary>
/// <param name="pack">The CashPack to solve.</param>
/// <returns>The solved plaintext payload.</returns>
public static byte[] Solve(CashPack pack)
{
byte[] currentKey = new byte[pack.Key.Length];
Array.Copy(pack.Key, 0, currentKey, 0, pack.Key.Length);
byte[] solveWorkspace = new byte[pack.Payload.Length];
while (true)
{
for (int i = 0; i < pack.Payload.Length; i++)
{
solveWorkspace[i] = (byte)(pack.Payload[i] ^ currentKey[i]);
}
// IMPORTANT: Use HMAC instead of Checksum
// This prevents you to do attacks where you can correlate known payloads
// And a CashPack without ever solving it.
using (HMACSHA512 sha = new HMACSHA512(currentKey))
{
byte[] hash = sha.ComputeHash(solveWorkspace);
bool failed = false;
for (int i = 0; i < pack.Hash.Length; i++)
{
if (pack.Hash[i] != hash[i])
{
failed = true;
break;
}
}
if (!failed)
{
return(solveWorkspace);
}
}
// Increment key
ulong keyAsNumber = BitHelper.KeyToNumber(currentKey, pack.BitDifficulty);
BitHelper.SetLastBitNumberBytes(currentKey, keyAsNumber + 1, pack.BitDifficulty);
}
}
/// <summary>
/// Packs a payload into a CashPack.
/// </summary>
/// <param name="payload">The plaintext payload to CashPack.</param>
/// <param name="bitDifficulty">The amount of bits to omit from the packed key. Calculator class can calculate this.</param>
/// <returns>The packed CashPack ready to distribute. It only contains the encrypted payload and reduced key.</returns>
public static CashPack Pack(byte[] payload, ushort bitDifficulty)
{
CashPack pack = new CashPack()
{
BitDifficulty = bitDifficulty,
};
// Alloc key
byte[] fullKey = new byte[payload.Length];
// Create key
using (RNGCryptoServiceProvider rng = new RNGCryptoServiceProvider())
{
rng.GetBytes(fullKey);
}
// HMAC Key
using (HMACSHA512 sha = new HMACSHA512(fullKey))
{
pack.Hash = sha.ComputeHash(payload);
}
// Alloc payload
pack.Payload = new byte[payload.Length];
// Encrypt payload
for (int i = 0; i < pack.Payload.Length; i++)
{
pack.Payload[i] = (byte)(payload[i] ^ fullKey[i]);
}
// Reduce key
byte[] reducedKey = fullKey;
BitHelper.ReduceKey(reducedKey, bitDifficulty);
pack.Key = reducedKey;
return(pack);
}
