VBA – Hashing in Excel with HMACSHA1

Hashing strings in general is useful. It is one of the good things, that we get from granted by the various .Net libraries and we should not try to do on our own, as the HMACSHA1 is quite a powerful algorithm, providing good hashes.

If, by any chance you are wondering how to get a HMACSHA1, encoded in BASE64, then you are on the right place. The two functions below will show you how:

Public Function Base64Sha1(inputText As String, Optional secretKey = "") As String

    Dim asc As Object
    Dim enc As Object
    Dim textToHash() As Byte
    Dim SharedSecretKey() As Byte
    Dim bytes() As Byte
    
    If secretKey = "" Then secretKey = inputText
    
    Set asc = CreateObject("System.Text.UTF8Encoding")
    Set enc = CreateObject("System.Security.Cryptography.HMACSHA1")

    textToHash = asc.GetBytes_4(inputText)
    SharedSecretKey = asc.GetBytes_4(secretKey)
    enc.Key = SharedSecretKey

    bytes = enc.ComputeHash_2((textToHash))
    Base64Sha1 = EncodeBase64(bytes)

End Function

Private Function EncodeBase64(arrData() As Byte) As String

    Dim objXML As Object
    Dim objNode As Object

    Set objXML = CreateObject("MSXML2.DOMDocument")
    Set objNode = objXML.createElement("b64")

    objNode.DataType = "bin.base64"
    objNode.nodeTypedValue = arrData
    EncodeBase64 = objNode.text

End Function

Sub TestMe()
    
    Debug.Print Base64Sha1("asdf", "ThisIsTheSecretKey") = "DSmGEC8dUW9xRs+YfAPji59dxCM="
    Debug.Print Base64Sha1("asdf") = "qIQmNGgreJRqJroWUUu0MxLq2oo="
    Debug.Print Base64Sha1("asdf", "asdf") = "qIQmNGgreJRqJroWUUu0MxLq2oo="
    
End Sub

That’s all! Quite ok for Excel.