Develop Reference

Storing 4x 0-16 numbers in a short (or 2 numbers in a byte)

I'm packing some binary data as a short, but want to have 4x values of 0-F.. And would like to do this without having a bunch of switch() cases reading the string.split of a hex
Someone have a clever, elegant solution for this or should I just long-hand it?
eg; 1C4A = (1, 12, 4, 10)

Shift in and out
var a = 1;
var b = 12;
var c = 4;
var d = 10;
// in
var packed = (short) ((a << 12) | (b << 8) | (c << 4) | d);
// out
a = (packed >> 12) & 0xf;
b = (packed >> 8) & 0xf;
c = (packed >> 4) & 0xf;
d = packed & 0xF;
Console.WriteLine(a);
Console.WriteLine(b);
Console.WriteLine(c);
Console.WriteLine(d);
Output
1
12
4
10

You can shift by 4 (or divide and multiply by 16) to move numbers into different place values. Then mask and shift your packed number to get your original numbers back.
Eg if you want to store 1 and 2 you could do:
int packed = (1 << 4) + 2;
int v1 = (packed & 0xF0) >> 4;
int v2 = packed & 0x0F;
Console.WriteLine($"{v1}, {v2}");
>>> 1, 2

Byte shift issue in an integer conversion

I read 3 bytes in a binary file which I need to convert into an integer.
I use this code to read the bytes :
LastNum last1Hz = new LastNum();
last1Hz.Freq = 1;
Byte[] LastNumBytes1Hz = new Byte[3];
Array.Copy(lap_info, (8 + (32 * k)), LastNumBytes1Hz, 0, 3);
last1Hz.NumData = LastNumBytes1Hz[2] << 16 + LastNumBytes1Hz[1] << 8 + LastNumBytes1Hz[0];
last1Hz.NumData is an integer.
This seems to be the good way to convert bytes into integers in the posts i have seen.
Here is a capture of the values read:
But the integer last1Hz.NumData is always 0.
I'm missing something but can't figure out what.

You need to use brackets (because addition has a higher priority than bit shifting):
int a = 0x87;
int b = 0x00;
int c = 0x00;
int x = c << 16 + b << 8 + a; // result 0
int z = (c << 16) + (b << 8) + a; // result 135
Your code should look like this:
last1Hz.NumData = (LastNumBytes1Hz[2] << 16) + (LastNumBytes1Hz[1] << 8) + LastNumBytes1Hz[0];

I think the problem is an order of precedence issue. + is evaluated before <<
Put brackets in to force the bit shift to be evaluated first.
last1Hz.NumData = (LastNumBytes1Hz[2] << 16) + (LastNumBytes1Hz[1] << 8) + LastNumBytes1Hz[0];

BitShifting for uint in c#

If I want to convert 4 bytes into an int, I can do this:
byte[] b = BitConverter.GetBytes(i1);
int i2 = BitConverter.ToInt32(b,0);
int i3 = b[0] | (b[1]<<8) | (b[2]<<16) | (b[3]<<24);
and then i1,i2,i3 will all equal.
but how do I do the same for a uint? This:
uint u1 = uint.MaxValue-1000;
byte[] b = BitConverter.GetBytes(u1);
uint u2 = BitConverter.ToUInt32(b,0);
uint u3 = (uint)(b[0] | (b[1]<<8) | (b[2]<<16) | (b[3]<<24));
results in a overlflow for large uints.

It would only throw that exception if in a checked context. See: http://msdn.microsoft.com/en-us/library/y3d0kef1(v=vs.80).aspx.
No exception:
uint u1 = uint.MaxValue - 1000;
byte[] b = BitConverter.GetBytes(u1);
uint u2 = BitConverter.ToUInt32(b, 0);
uint u3 = (uint) (b[0] | (b[1] << 8) | (b[2] << 16) | (b[3] << 24));
exception:
checked
{
uint u1 = uint.MaxValue - 1000;
byte[] b = BitConverter.GetBytes(u1);
uint u2 = BitConverter.ToUInt32(b, 0);
uint u3 = (uint) (b[0] | (b[1] << 8) | (b[2] << 16) | (b[3] << 24));
}
no exception
checked
{
unchecked
{
uint u1 = uint.MaxValue - 1000;
byte[] b = BitConverter.GetBytes(u1);
uint u2 = BitConverter.ToUInt32(b, 0);
uint u3 = (uint) (b[0] | (b[1] << 8) | (b[2] << 16) | (b[3] << 24));
Console.WriteLine(u1 + " " + u2 + " " + u3);
}
}
Make sure you're not compiling with the /checked option.
The exception is thrown by casting from int to uint. Using the shift operator on the bytes (the line with uint u3 = ...) implicitly cast them to int. A uint with the MSB on ("1") is a negative int which is out of range for uint. Using int causes no such exception because there is no explicit cast which might elicit an overflow exception.

I ran your code with uint values up to 4,294,967,295, which is the max and it works fine in all cases.

Blowfish Invalid Length Exception

I'm encrypting my file with Blowfish algorithm but it seems that I don't know something about it. Whenever I try to Encipher() it will throw an exception that says 'Invalid Length'. I figured that the length must be zero when it's getting mod with 8 and I think it means there should be 8 by 8 blocks of stream to start encipher. What should I do?
Encipher method of Blowfish:
public void Encipher(byte[] data, int length)
{
uint xl, xr;
if ((length % 8) != 0) <-- Exception Line
throw new Exception("Invalid Length");
for (int i = 0; i < length; i += 8)
{
// Encode the data in 8 byte blocks.
xl = (uint)((data[i] << 24) | (data[i + 1] << 16) | (data[i + 2] << 8) | data[i + 3]);
xr = (uint)((data[i + 4] << 24) | (data[i + 5] << 16) | (data[i + 6] << 8) | data[i + 7]);
Encipher(ref xl, ref xr);
// Now Replace the data.
data[i] = (byte)(xl >> 24);
data[i + 1] = (byte)(xl >> 16);
data[i + 2] = (byte)(xl >> 8);
data[i + 3] = (byte)(xl);
data[i + 4] = (byte)(xr >> 24);
data[i + 5] = (byte)(xr >> 16);
data[i + 6] = (byte)(xr >> 8);
data[i + 7] = (byte)(xr);
}
}
My encryption method:
private void EncryptFile(string szFilePath, string szInfoFile, string szKey, string szEncryptedFile = "")
{
// Blowfish
Blowfish alg = new Blowfish(Encoding.Unicode.GetBytes(szKey));
// Open file
System.IO.FileStream originalStream = System.IO.File.OpenRead(szFilePath);
// Store original file length
long originalLength = originalStream.Length;
System.IO.File.WriteAllText(szInfoFile, originalLength.ToString());
Byte[] buffer = new byte[originalStream.Length + (originalStream.Length % 8)];
originalStream.Read(buffer, 0, buffer.Length);
originalStream.Close();
// Encrypt
alg.Encipher(buffer, buffer.Length);
string szEncFile;
if (szEncryptedFile != string.Empty) szEncFile = szEncryptedFile; else szEncFile = szFilePath;
System.IO.FileStream stream = new System.IO.FileStream(szEncFile, System.IO.FileMode.Create);
stream.Write(buffer, 0, buffer.Length);
stream.Close();
}
Thanks.

If what you're trying to do is round a value up to the next value divisible by 8, then you should do this instead:
Byte[] buffer = new byte[originalStream.Length + (8-(originalStream.Length % 8))];

Peter Ritchie answered it. However, there are a couple of idiomatic pieces you should consider below. One is wrapping IDisposable-implemented classes (such as FileStreams) in using blocks in order to ensure disposal of the resources in the case of exceptional conditions during processing. Another is the if..then you put in one line. It's really .. odd. I've replaced it with the ternary operator, which seems to fit the usage you're employing. Best of luck.
private void EncryptFile(string szFilePath, string szInfoFile, string szKey, string szEncryptedFile = "")
{
// Blowfish
Blowfish alg = new Blowfish(Encoding.Unicode.GetBytes(szKey));
// Open file
using (System.IO.FileStream originalStream = System.IO.File.OpenRead(szFilePath))
{
// Store original file length
long originalLength = originalStream.Length;
System.IO.File.WriteAllText(szInfoFile, originalLength.ToString());
Byte[] buffer = new byte[originalStream.Length + (originalStream.Length % 8)];
originalStream.Read(buffer, 0, buffer.Length);
}
// Encrypt
alg.Encipher(buffer, buffer.Length);
string szEncFile;
szEncFile = string.IsNullOrEmpty(szEncryptedFile) ? szFilePath : szEncryptedFile;
using (System.IO.FileStream stream = new System.IO.FileStream(szEncFile, System.IO.FileMode.Create))
{
stream.Write(buffer, 0, buffer.Length);
}
}

Encode / Decode RealVNC password

I'm trying to write C# application that can remotely change the RealVNC password on another box.
What works currently is that I can pull a password from a box that has already been changed, store it as a hex string, and then send it to another box AND then change the password that way but I need to be able to change the password or randomize it on the fly.
I'm having problems with creating the correct binary to place in the registry.
I know the VNC key:
byte[] Key = { 23, 82, 107, 6, 35, 78, 88, 7 };
So using the above key and passing "1234" as the password to encrypt using the following code:
public static byte[] EncryptTextToMemory(string Data, byte[] Key)
{
try
{
MemoryStream mStream = new MemoryStream()
DESCryptoServiceProvider desProvider = new DESCryptoServiceProvider();
desProvider.Mode = CipherMode.ECB;
desProvider.Key = Key;
CryptoStream cStream = new CryptoStream(mStream,
desProvider.CreateEncryptor(),
CryptoStreamMode.Write);
byte[] toEncrypt = new ASCIIEncoding().GetBytes(Data);
cStream.Write(toEncrypt, 0, toEncrypt.Length);
cStream.FlushFinalBlock();
byte[] ret = mStream.ToArray();
cStream.Close();
mStream.Close();
return ret;
}
catch (CryptographicException ex)
{
MessageBox.Show("A Cryptographic error occurred: " + ex.Message);
return null;
}
After passing the returned byte array to BitConverter.ToString, I would expect to get the same hex values as stored in the registry of a password already set to 1234 with RealVNC itself, but I'm not.

Here are my sources to encrypt/decrypt VNC password:
public static string EncryptVNC(string password)
{
if (password.Length > 8)
{
password = password.Substring(0, 8);
}
if (password.Length < 8)
{
password = password.PadRight(8, '\0');
}
byte[] key = { 23, 82, 107, 6, 35, 78, 88, 7 };
byte[] passArr = new ASCIIEncoding().GetBytes(password);
byte[] response = new byte[passArr.Length];
char[] chars = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F' };
// reverse the byte order
byte[] newkey = new byte[8];
for (int i = 0; i < 8; i++)
{
// revert desKey[i]:
newkey[i] = (byte)(
((key[i] & 0x01) << 7) |
((key[i] & 0x02) << 5) |
((key[i] & 0x04) << 3) |
((key[i] & 0x08) << 1) |
((key[i] & 0x10) >> 1) |
((key[i] & 0x20) >> 3) |
((key[i] & 0x40) >> 5) |
((key[i] & 0x80) >> 7)
);
}
key = newkey;
// reverse the byte order
DES des = new DESCryptoServiceProvider();
des.Padding = PaddingMode.None;
des.Mode = CipherMode.ECB;
ICryptoTransform enc = des.CreateEncryptor(key, null);
enc.TransformBlock(passArr, 0, passArr.Length, response, 0);
string hexString = String.Empty;
for (int i = 0; i < response.Length; i++)
{
hexString += chars[response[i] >> 4];
hexString += chars[response[i] & 0xf];
}
return hexString.Trim().ToLower();
}
And to decrypt:
public static string DecryptVNC(string password)
{
if (password.Length < 16)
{
return string.Empty;
}
byte[] key = { 23, 82, 107, 6, 35, 78, 88, 7 };
byte[] passArr = ToByteArray(password);
byte[] response = new byte[passArr.Length];
// reverse the byte order
byte[] newkey = new byte[8];
for (int i = 0; i < 8; i++)
{
// revert key[i]:
newkey[i] = (byte)(
((key[i] & 0x01) << 7) |
((key[i] & 0x02) << 5) |
((key[i] & 0x04) << 3) |
((key[i] & 0x08) << 1) |
((key[i] & 0x10) >> 1) |
((key[i] & 0x20) >> 3) |
((key[i] & 0x40) >> 5) |
((key[i] & 0x80) >> 7)
);
}
key = newkey;
// reverse the byte order
DES des = new DESCryptoServiceProvider();
des.Padding = PaddingMode.None;
des.Mode = CipherMode.ECB;
ICryptoTransform dec = des.CreateDecryptor(key, null);
dec.TransformBlock(passArr, 0, passArr.Length, response, 0);
return System.Text.ASCIIEncoding.ASCII.GetString(response);
}
Also this function is needed:
public static byte[] ToByteArray(String HexString)
{
int NumberChars = HexString.Length;
byte[] bytes = new byte[NumberChars / 2];
for (int i = 0; i < NumberChars; i += 2)
{
bytes[i / 2] = Convert.ToByte(HexString.Substring(i, 2), 16);
}
return bytes;
}
At top add:
using System.Security.Cryptography;
Can't remember where I got the code from. I am not the original author.