HMAC Algorithm (SHA256) in Classic ASP VBScript

Question

I\'m trying to write an HMAC function in Classic ASP using SHA256 as the hash. I thought I got it right, but the results aren\'t the same for the examples listed on the Wiki

Answer 1

The issue is because VBScript String is not a bytearray, so when you concat chr(0) you are adding 2 0 bytes to string.

Anyway VBScript is a nighmare for managing bytes and words, so I suggest you use a crypt javascript API that we have wrapped for ASP VBScript use.

You could get more details, and our contact info in this repository: https://github.com/ictmanagement/redsysHMAC256_API_ASP

A complete example:

'/******  MAC Function ******/
'Input String|WordArray , Returns WordArray
Function mac256(ent, key) 
    Dim encWA
    Set encWA = ConvertUtf8StrToWordArray(ent)
    Dim keyWA
    Set keyWA = ConvertUtf8StrToWordArray(key)
    Dim resWA
    Set resWA = CryptoJS.HmacSHA256(encWA, keyWA)
    Set mac256 = resWA
End Function

'Input (Utf8)String|WordArray Returns WordArray
Function ConvertUtf8StrToWordArray(data)
    If (typename(data) = "String") Then
        Set ConvertUtf8StrToWordArray = CryptoJS.enc.Utf8.parse(data)
    Elseif (typename(data) = "JScriptTypeInfo") Then
        On error resume next
        'Set ConvertUtf8StrToWordArray = CryptoJS.enc.Utf8.parse(data.toString(CryptoJS.enc.Utf8)) 
        Set ConvertUtf8StrToWordArray = CryptoJS.lib.WordArray.create().concat(data) 'Just assert that data is WordArray
        If Err.number>0 Then
            Set ConvertUtf8StrToWordArray = Nothing
        End if
        On error goto 0
    Else
        Set ConvertUtf8StrToWordArray = Nothing
    End if
End Function

Dim test
test = "Hi guys"
key = "guyb u oisd qiu dqid qew" 'You could create a WordArray from Hex String, Utf8 String, etc.
Dim res
res = mac256(test,key) 'Result is a WordArray, so
Response.Write res.toString(CryptoJS.enc.Hex)