RC4 encryption algo bit level question

Hi Experts,

I am using the functions below to provide an RC4 encryption to some sensitive fields in a website. I have the following question:

On the following line:

dim ET_RC4_40bitKey : ET_RC4_40bitKey="s0W3a" '*** Only 5 characters allowed in UK (40-bit encryption law)

The 40 bit key is defined. It appears to me that the encryption level is set at 40 bit because there are five characters in the encryption key. Is this correct? and if so how do I encrease the encryption to 128 bit?

Basically I am trying to work out the formula for #characters to encryption bit level.


Any ideas?



Thanks,




PJORDANNA







'*** Arrays for the RC4 Encryptions algorithms
Dim RC4_sbox(255)
Dim RC4_keyArray(255)
dim ET_RC4_40bitKey : ET_RC4_40bitKey="s0W3a" '*** Only 5 characters allowed in UK (40-bit encryption law)

Sub RC4Initialize(strPwd)
'**** This routine called by RC4EnDeCrypt function. Initializes the RC4_sbox and the RC4_keyArray array.

   dim tempSwap
   dim a
   dim b

   intLength = len(strPwd)
   For a = 0 To 255
      RC4_keyArray(a) = asc(mid(strpwd, (a mod intLength)+1, 1))
      RC4_sbox(a) = a
   next

   b = 0
   For a = 0 To 255
      b = (b + RC4_sbox(a) + RC4_keyArray(a)) Mod 256
      tempSwap = RC4_sbox(a)
      RC4_sbox(a) = RC4_sbox(b)
      RC4_sbox(b) = tempSwap
   Next
End Sub

Function RC4EnDeCrypt(plaintxt, psw)
      '*** Performs the encrption/decryption
      '*** Note using more than a 5 character password would be illegal in the UK - only 40 bit encryption allowed
   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 + RC4_sbox(i)) Mod 256
      temp = RC4_sbox(i)
      RC4_sbox(i) = RC4_sbox(j)
      RC4_sbox(j) = temp

      k = RC4_sbox((RC4_sbox(i) + RC4_sbox(j)) Mod 256)

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

   RC4EnDeCrypt = cipher

End Function

function charStrToHexCodes(charStr) '*** generates a hex byte string from a character string
      charStrToHexCodes=""
      for qq = 1 to len(charStr)
            charStrToHexCodes=charStrToHexCodes & right(string(2,"0") & hex(asc(mid(charStr, qq, 1))),2)                   
      next
end function

function hexCodesToCharStr(hexCodes) '*** generates a character string from a hex byte string
      dim i
      hexCodesToCharStr=""
      if len(hexCodes)/2 <> Int(len(hexCodes)/2) then exit function
      for i=1 to len(hexCodes)-1 step 2
            hexCodesToCharStr=hexCodesToCharStr&Chr(hexByteToDecimal(Mid(hexCodes,i,2)))
      next
end function

function hexDigitToDecimal(digit) '*** Converts a single hex digit to decimal, returns -1 if not possible
      select case digit
      case "0","1","2","3","4","5","6","7","8","9"
            hexDigitToDecimal=CInt(digit)
      case "A","a"
            hexDigitToDecimal=10
      case "B","b"
            hexDigitToDecimal=11
      case "C","c"
            hexDigitToDecimal=12
      case "D","d"
            hexDigitToDecimal=13
      case "E","e"
            hexDigitToDecimal=14
      case "F","f"
            hexDigitToDecimal=15
      case else
            hexDigitToDecimal=-1
      end select
end function

function hexByteToDecimal(byteStr) '*** Converts a hex byte to decimal, returns -1 if not possible
      if (len(byteStr)<>2 or hexDigitToDecimal(Left(byteStr,1))=-1 or hexDigitToDecimal(Right(byteStr,1))=-1) then
            hexByteToDecimal=-1
            exit function
      end if
      hexByteToDecimal=hexDigitToDecimal(Left(byteStr,1))*16+hexDigitToDecimal(Right(byteStr,1))
end function