Excel Macro: Base64 HMAC Encryption

Some APIs require each REST request to be signed with an HMAC SHA256 signature, and these signatures need to be converted to base64. This custom function calculates HMAC SHA1, SHA256, SHA384 or SHA512 with Base64 encoding. To use this code, you need do this:

1. Download and install the .NET Framework 3.5, only working in .NETFramework 3.5.
2. Inside the VBE, Go to Tools -> References, then Select Microsoft XML, v6.0 (or whatever your latest is. This will give you access to the XML Object Library.)

Base64 HMAC Encryption

'------------------ Modules ------------------
Public Function Base64HMAC(ByVal sType As String, ByVal sTextToHash As String, ByVal sSharedSecretKey As String)
    'sType: SHA1, SHA256, SHA384, SHA512
    Dim asc As Object, enc As Object
    Dim TextToHash() As Byte
    Dim SharedSecretKey() As Byte
    
    Set asc = CreateObject("System.Text.UTF8Encoding")  'only working in .NET Framework 3.5
    sType = UCase(sType)
    Select Case sType
    Case "SHA1"
        Set enc = CreateObject("System.Security.Cryptography.HMACSHA1")
    Case "SHA256"
        Set enc = CreateObject("System.Security.Cryptography.HMACSHA256")
    Case "SHA384"
        Set enc = CreateObject("System.Security.Cryptography.HMACSHA384")
    Case "SHA512"
        Set enc = CreateObject("System.Security.Cryptography.HMACSHA512")
    Case Else
        Base64HMAC = "Error! sType value: SHA1, SHA256, SHA384, SHA512"
        Exit Function
    End Select

    TextToHash = asc.Getbytes_4(sTextToHash)
    SharedSecretKey = asc.Getbytes_4(sSharedSecretKey)
    enc.Key = SharedSecretKey

    Dim bytes() As Byte
    bytes = enc.ComputeHash_2((TextToHash))
    Base64HMAC = EncodeBase64(bytes)

    Set asc = Nothing
    Set enc = Nothing
End Function

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

    'Inside the VBE, Go to Tools -> References, then Select Microsoft XML, v6.0
    '(or whatever your latest is. This will give you access to the XML Object Library.)

    Dim objXML As MSXML2.DOMDocument60
    Dim objNode As MSXML2.IXMLDOMElement

    Set objXML = New MSXML2.DOMDocument60

    ' byte array to base64
    Set objNode = objXML.createElement("b64")
    objNode.DataType = "bin.base64"
    objNode.nodeTypedValue = arrData
    EncodeBase64 = objNode.Text

    Set objNode = Nothing
    Set objXML = Nothing
End Function

Examples

You can test the code in the VBE Immediate Window with the Debug.Print method, for example:

run this code in Immediate Window:

debug.Print Base64HMAC("sha256","YourText","YourKey")

Result:

KTGtkOlKXYiF0s7yyzTZr9utrHfSuY0KE+kJLT1zetA=

or use as worksheet function:

Base64 HMAC SHA1

=Base64HMAC("sha1","abc","1234567890")

Base64 HMAC SHA256

=Base64HMAC("sha256","abc","1234567890")

Base64 HMAC SHA384

=Base64HMAC("sha384","abc","1234567890")

Base64 HMAC SHA512

=Base64HMAC("sha512","abc","1234567890")

Check Result

Check result here: Hash and HMAC calculator

Base64 HMAC SHA256 in different languages

If you need examples of creating base64 hashes using HMAC SHA256 in different languages (Javascript, PHP, Java, Groovy, C#, Objective C, Go, Ruby, Python, Perl, Dart, Swift, Rust, Powershell, Shell), read this post.

How to Use This Macro