Can I use DPAPI (or something like it) in VBA? - excel

Question

another in my beginnerish series of questions about VBA.
I am in the process of writing an Excel add-in in VBA, and the add-in uses a local configuration file.
This file needs to contain a password for a remote service.
Obviously, it is less than ideal to store this password as plaintext. But I am looking for an algorithm that can encode/decode text so it at least doesn't look like plaintext in the configuration file.
I came across a reference to Windows DPAPI but I'm not sure whether this is an appropriate solution for Excel VBA. I also am not sure how I can use this API from within VBA, as I've only found references to using it with .NET. Visual Studio is unavailable to this project.
So the 2-part question is this:
1) If it is possible to use DPAPI from within VBA, can I have an example of its use?
2) If it is not possible to use DPAPI in VBA, do you have any suggestions for how to store text in some encoded fashion that is reversible?
The solution must work in Excel 2003 and later, if it matters.
Thank you once again.

Answer 1

The solution must work in Excel 2003 and later, if it matters.
For Excel VBA, I suggest using the CAPICOM Library.
Download the file from here. Once it is installed, follow these instructions for registering the Dll.
32 bit OS
Copy the file Capicom.dll from the C:\Program Files\Microsoft CAPICOM 2.1.0.2 SDK\Lib to C:\Windows\System32
Next on Start Menu | Run , type this
Regsvr32 C:\Windows\System32\Capicom.dll
64 bit OS
Copy the file Capicom.dll from the C:\Program Files (x86)\Microsoft CAPICOM 2.1.0.2 SDK\Lib\X86 to C:\Windows\SysWOW64
Next on Start Menu | Run , type this
Regsvr32 C:\Windows\SysWOW64\Capicom.dll
Now we are set to use it in our VBA Project
Paste this code in a module
Option Explicit
Sub Sample()
Dim TextToEncrypt As String, EncryptedText As String
Dim TextToDeCrypt As String, DeCryptedText As String
Dim KeyToEncrypt As String
TextToEncrypt = "Hello World"
KeyToEncrypt = "JoshMagicWord"
EncryptedText = EncryptString(TextToEncrypt, KeyToEncrypt)
DeCryptedText = DecryptString(EncryptedText, KeyToEncrypt)
Debug.Print "The string " & TextToEncrypt & " after encryption looks like this"
Debug.Print "-----------------------------------------------------------------"
Debug.Print EncryptedText
Debug.Print "-----------------------------------------------------------------"
Debug.Print "The above string after decrypting looks like this"
Debug.Print "-----------------------------------------------------------------"
Debug.Print DeCryptedText
End Sub
Public Function EncryptString(strText As String, ky As String) As String
Dim Cap As Object
Dim cryptIt
Set Cap = CreateObject("CAPICOM.EncryptedData")
Cap.Algorithm = 3
Cap.SetSecret ky
Cap.Content = strText
EncryptString = Cap.Encrypt
End Function
Public Function DecryptString(strText As String, ky As String) As String
Dim Cap As Object
Dim cryptIt
Set Cap = CreateObject("CAPICOM.EncryptedData")
Cap.Algorithm = 3
Cap.SetSecret ky
Cap.Decrypt strText
DecryptString = Cap.Content
End Function
The function EncryptString encrypts the string and the function DecryptString decrypts the string. See snapshot of results when you run the above Sub Sample