I have this old webshop based on classis ASP that I want to use with Payment service provider Rabobank omnikassa 2 but I can's seem to find a script that I need that will accept HMAC512SHA encryption with a Base64 encoded key.
The webshop is build in VBscript and I managed to find some code however this will not accept a Base64 encoded key. I alread have a Base64 decoder script but need to make changes to the script below or have something else.

This is the code, I thisk that changes have to be made in line 44 at the marker ### to accept base64coded or decoded key, can't use UTF-8 string input.

<%
' Hash("sha512", "Hello World")
' Hash("sha512HMAC", Array("Hello World", "Shared Key"))

Function Hash(HashType, Target)
On Error Resume Next
Dim PlainText

If IsArray(Target) = True Then PlainText = Target(0) Else PlainText = Target End If

' create UTF-8 string
With CreateObject("ADODB.Stream")
.Open
.CharSet = "Windows-1252"
.WriteText PlainText
.Position = 0
.CharSet = "UTF-8"
PlainText = .ReadText
.Close
End With

Set UTF8Encoding = CreateObject("System.Text.UTF8Encoding")

Dim PlainTextToBytes, BytesToHashedBytes, HashedBytesToHex
PlainTextToBytes = UTF8Encoding.GetBytes_4(PlainText)

Select Case HashType
Case "md5": Set Cryptography = CreateObject("System.Security.Cryptography.MD5CryptoServiceProvider") '< 64 (collisions found)
Case "ripemd160": Set Cryptography = CreateObject("System.Security.Cryptography.RIPEMD160Managed")
Case "sha1": Set Cryptography = CreateObject("System.Security.Cryptography.SHA1Managed") '< 80 (collision found)
Case "sha256": Set Cryptography = CreateObject("System.Security.Cryptography.SHA256Managed")
Case "sha384": Set Cryptography = CreateObject("System.Security.Cryptography.SHA384Managed")
Case "sha512": Set Cryptography = CreateObject("System.Security.Cryptography.SHA512Managed")
Case "md5HMAC": Set Cryptography = CreateObject("System.Security.Cryptography.HMACMD5")
Case "ripemd160HMAC": Set Cryptography = CreateObject("System.Security.Cryptography.HMACRIPEMD160")
Case "sha1HMAC": Set Cryptography = CreateObject("System.Security.Cryptography.HMACSHA1")
Case "sha256HMAC": Set Cryptography = CreateObject("System.Security.Cryptography.HMACSHA256")
Case "sha384HMAC": Set Cryptography = CreateObject("System.Security.Cryptography.HMACSHA384")
Case "sha512HMAC": Set Cryptography = CreateObject("System.Security.Cryptography.HMACSHA512")
End Select

Cryptography.Initialize()

' ### the line below does not accept bsae64 decoded string
If IsArray(Target) = True Then Cryptography.Key = UTF8Encoding.GetBytes_4(target(1)) End If
BytesToHashedBytes = Cryptography.ComputeHash_2((PlainTextToBytes))

For x = 1 To LenB(BytesToHashedBytes)
HashedBytesToHex = HashedBytesToHex & Right("0" & Hex(AscB(MidB(BytesToHashedBytes, x, 1))), 2)
Next

If Err.Number <> 0 Then Response.Write(Err.Description) Else Hash = LCase(HashedBytesToHex) End If
On Error GoTo 0
End Function
%>

Can anybody help me with this ?
Al my other coding is done and I need to fix this, any suggestions.
Thanks