I saw this nifty article which describes how to add the .NET framwork itself
as a reference to your VB6 project. (Guys don't jump on me, this is a VB6,
not a .NET question - please see code below.)

Anyway, I'm trying to use the .NET framework to do 3DES encryption inside my
VB6 application, but I'm running into a couple of snags: (BTW, this function
works properly in the equivalent .NET application, but I need to duplicate
this in VB6 since we're providing both VB6 and .NET clients.)

First of all, this statement doesn't compile:

  zEncrypt = Convert.ToBase64String(DESEncrypt.TransformFinalBlock(Buffer,
0, UBound(Buffer)))

The error is Function or interface marked as restricted, or the function
uses an automation type not supported in Visual Basic. The method parameters
are byte[], int and int so I'm not sure what the problem is.

The second problem is that this statement does something really funky at
runtime: (I compiled by commenting out the offending statement above.) At
runtime (in the IDE) this statement simply exits the function. No Err is
tripped, just bingo, back to the next statement in the calling function.

  DES.Key = hashMD5.ComputeHash(ASCIIEnc.ASCII.GetBytes("12345678"))

If you have a solution or if you can propose a better way for me to do 3DES
encryption in VB6, that will help me immensely.

Thanks!

- Joe Geretz -

Private Function zEncrypt(ByVal Plaintext As String) As String

  Dim DES        As TripleDESCryptoServiceProvider
  Dim hashMD5    As MD5CryptoServiceProvider
  Dim DESEncrypt As ICryptoTransform
  Dim Buffer()   As Byte
  Dim ASCIIEnc   As ASCIIEncoding

  Set DES = New TripleDESCryptoServiceProvider
  Set hashMD5 = New MD5CryptoServiceProvider
  Set ASCIIEnc = New ASCIIEncoding

  Set DES.Key = hashMD5.ComputeHash(ASCIIEnc.ASCII.GetBytes("12345678"))
  DES.Mode = CipherMode_ECB

  Set DESEncrypt = DES.CreateEncryptor

  Buffer = ASCIIEnc.ASCII.GetBytes(Plaintext)

  zEncrypt = Convert.ToBase64String(DESEncrypt.TransformFinalBlock(Buffer,
0, UBound(Buffer)))

End Function