Re: how these 2 functions may differ?

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Hello Ben,

thanks for the reply. The original encryption and base64 encoding is done from a Windows Script Host vbscript. The c# end of this is a web app that must decode/decrypt this data.

I attached vbscript code that does the encryption/encoding if you want to see. Also, a copy/paste of a c# translation of this, which is what I'm using on the web app to try to decode/decrypt is below....

public class RC4Utility
{
// This is a translation of Mike Shaffer's vbscript code for RC4 done by Chris Scott.
// From 4guysfromrolla.com

protected int[] sbox = new int[256];
protected int[] key = new int[256];

protected string plaintext, password;

public string PlainText
{
set { plaintext = value; }
get { return plaintext; }
}

public string Password
{
set { password = value; }
get { return password; }
}

private void RC4Initialize(string strPwd)
{

int intLength = strPwd.Length;

for (int a = 0; a <= 255; a++)
{

char ctmp = (strPwd.Substring((a % intLength), 1).ToCharArray()[0]);

key[a] = Microsoft.VisualBasic.Strings.Asc(ctmp);
sbox[a] = a;
}

int x = 0;

for (int b = 0; b <= 255; b++)
{
x = (x + sbox[b] + key[b]) % 256;
int tempSwap = sbox[b];
sbox[b] = sbox[x];
sbox[x] = tempSwap;
}
}

public string EnDeCrypt()
{
int i = 0;
int j = 0;
string cipher = "";

RC4Initialize(password);

for (int a = 1; a <= plaintext.Length; a++)
{

int itmp = 0;

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];

char ctmp = plaintext.Substring(a - 1, 1).ToCharArray()[0];

itmp = Microsoft.VisualBasic.Strings.Asc(ctmp);

int cipherby = itmp ^ k;

cipher += Microsoft.VisualBasic.Strings.Chr(cipherby);
}

return cipher;
}

}


"Ben Voigt [C++ MVP]" <rbv@xxxxxxxxxxxxx> wrote in message news:uS4I8pPcJHA.4412@xxxxxxxxxxxxxxxxxxxxxxx
James wrote:
yes, I'm pretty sure they are. I am sure that the text representation
of them on screen (displayed in text box control) is identical.

I see the vbscript code formatting was lost in my post... I'll try to
attach in a .txt file (windows notepad.exe)

I'm reading through msdn docs now and I'm thinking this has something
to do with the fact that the rc4 cipher is using ascii characters
0-255 and the .net asciiEncoding class only uses 0-127.... maybe I
need to add a step where I change the encrypted text to unicode, then
base64 it?

Encrypted text is not text. It is binary data. I suggest you stop using a string to hold it. Doesn't the encryption routine give you a byte[] out? And the Base-64 encoding functions take a byte[] as input. No Unicode needed, no encoding needed, just pass the byte[].




"Family Tree Mike" <FamilyTreeMike@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote in
message news:474F2B84-167E-4113-B368-89AD0C327D1A@xxxxxxxxxxxxxxxx


"James" wrote:

Hello,

I'm having an issue that a previously posted on but after
re-reading that post I realize its a mess and it would be a real
pain for someone to lend a
hand based on that.. so here is a much more direct question:

could anyone tell just how these .net base64 functions differ from
the vbscript base64 functions? When using them if I encode the text
'test' I get
the same result from them all, however, if I first RC4 encrypt the
text 'test' and then encode that, the results differ between the
vbscript and ..net functions?


Are the encrypted strings in both cases identical?

Mike


'--------------------------------------------------------------------
'start: Mike Shaffer's RC4 functions --------------------------------
'--------------------------------------------------------------------

Dim sbox(255)
Dim key(255)


Sub RC4Initialize(strPwd)
':::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
'::: This routine called by EnDeCrypt function. Initializes the :::
'::: sbox and the key array) :::
':::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::

dim tempSwap
dim a
dim b
'below added to Mike Shaffer's code only to comply with Option Explicit
Dim intLength

intLength = len(strPwd)
For a = 0 To 255
key(a) = asc(mid(strpwd, (a mod intLength)+1, 1))
sbox(a) = a
next

b = 0
For a = 0 To 255
b = (b + sbox(a) + key(a)) Mod 256
tempSwap = sbox(a)
sbox(a) = sbox(b)
sbox(b) = tempSwap
Next

End Sub

Function EnDeCrypt(plaintxt, psw)
':::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
'::: This routine does all the work. Call it both to ENcrypt :::
'::: and to DEcrypt your data. :::
':::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::

dim temp
dim a
dim i
dim j
dim k
dim cipherby
dim cipher

i = 0
j = 0

RC4Initialize psw

For a = 1 To Len(plaintxt)
i = (i + 1) Mod 256
j = (j + sbox(i)) Mod 256
temp = sbox(i)
sbox(i) = sbox(j)
sbox(j) = temp

k = sbox((sbox(i) + sbox(j)) Mod 256)

cipherby = Asc(Mid(plaintxt, a, 1)) Xor k
cipher = cipher & Chr(cipherby)
Next

EnDeCrypt = cipher

End Function

'----------------------------------------------------------------------------
'end: Mike Shaffer's RC4 code -----------------------------------------------
'----------------------------------------------------------------------------

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