RC4 Encryption non-alphanumeric wrong

Question

Background: I'm trying to convert Mike Shaffer's VB RC4 encryption to C# (http://www.4guysfromrolla.com/articles/091802-1.3.aspx). See a previous question of mine at Converting Mike Shaffer's RC4Encryption to C#.

It seems my encryption is not working.

Using the demo page at: http://www.4guysfromrolla.com/demos/rc4test.asp, with password of "abc":

Plain text: og;|Q{Fe should result in

A2 FA E2 55 09 A4 AB 16

However, my code is generating the 5th char as 9, instead of 09:

A2 FA E2 55 9 A4 AB 16

Another example - Plain text: cl**z!Ss should result in

AE F1 F3 03 22 FE BE 00

However, my code is generating:

AE F1 F3 3 22 FE BE 0

It seems it's only a problem with certain non-alphanumeric characters.

Here's my code:

private static string EnDeCrypt(string text)
{
    int i = 0;
    int j = 0;
    string cipher = "";

    // Call our method to initialize the arrays used here.
    RC4Initialize(password);


    // Set up a for loop.  Again, we use the Length property
    // of our String instead of the Len() function
    for (int a = 1; a <= text.Length; a++)
    {
        // Initialize an integer variable we will use in this loop
        int itmp = 0;

        // Like the RC4Initialize method, we need to use the %
        // in place of Mod
        i = (i + 1) % 256;
        j = (j + sbox[i]) % 256;
        itmp = sbox[i];
        sbox[i] = sbox[j];
        sbox[j] = itmp;

        int k = sbox[(sbox[i] + sbox[j]) % 256];

        // Again, since the return type of String.Substring is a
        // string, we need to convert it to a char using
        // String.ToCharArray() and specifying that we want the
        // first value, [0].
        char ctmp = text.Substring(a - 1, 1).ToCharArray()
        [0];
        itmp = ctmp;  //there's an implicit conversion for char to int

        int cipherby = itmp ^ k;

        cipher += (char)cipherby; //just cast cipherby to a char 
    }

    // Return the value of cipher as the return value of our
    // method
    return cipher;
}

public static string ConvertAsciiToHex(string input)
{
    return string.Join(string.Empty, input.Select(c => Convert.ToInt32(c).ToString("X")).ToArray());
}

public static string Encrypt(string text)
{
    return ConvertAsciiToHex(EnDeCrypt(text));
}

Here's how I get my encrypted result:

var encryptedResult = RC4Encrypt.Encrypt(valuetoencrypt);

Answer 1

The output is correct (leading zeros don't change the value), your code is simply not padding values that fit into a single hex digit (such as 9 or 3 or 0). Use .ToString("X2") instead of .ToString("X").