Hashing a string with CryptoAPI

HashString

Private Declare Function CryptAcquireContext Lib "advapi32.dll" _
   Alias "CryptAcquireContextA" ( _
   ByRef phProv As Long, _
   ByVal pszContainer As String, _
   ByVal pszProvider As String, _
   ByVal dwProvType As Long, _
   ByVal dwFlags As Long) As Long

Private Declare Function CryptReleaseContext Lib "advapi32.dll" ( _
   ByVal hProv As Long, _
   ByVal dwFlags As Long) As Long

Private Declare Function CryptCreateHash Lib "advapi32.dll" ( _
   ByVal hProv As Long, _
   ByVal Algid As Long, _
   ByVal hKey As Long, _
   ByVal dwFlags As Long, _
   ByRef phHash As Long) As Long

Private Declare Function CryptDestroyHash Lib "advapi32.dll" ( _
   ByVal hHash As Long) As Long

Private Declare Function CryptHashData Lib "advapi32.dll" ( _
   ByVal hHash As Long, _
   pbData As Any, _
   ByVal dwDataLen As Long, _
   ByVal dwFlags As Long) As Long

Private Declare Function CryptGetHashParam Lib "advapi32.dll" ( _
   ByVal hHash As Long, _
   ByVal dwParam As Long, _
   pbData As Any, _
   pdwDataLen As Long, _
   ByVal dwFlags As Long) As Long

Private Const PROV_RSA_FULL = 1

Private Const ALG_CLASS_HASH = 32768

Private Const ALG_TYPE_ANY = 0

Private Const ALG_SID_MD2 = 1
Private Const ALG_SID_MD4 = 2
Private Const ALG_SID_MD5 = 3
Private Const ALG_SID_SHA1 = 4

Enum HashAlgorithm
   MD2 = ALG_CLASS_HASH Or ALG_TYPE_ANY Or ALG_SID_MD2
   MD4 = ALG_CLASS_HASH Or ALG_TYPE_ANY Or ALG_SID_MD4
   MD5 = ALG_CLASS_HASH Or ALG_TYPE_ANY Or ALG_SID_MD5
   SHA1 = ALG_CLASS_HASH Or ALG_TYPE_ANY Or ALG_SID_SHA1
End Enum

Private Const HP_HASHVAL = 2
Private Const HP_HASHSIZE = 4

Function HashString( _
   ByVal Str As String, _
   Optional ByVal Algorithm As HashAlgorithm = MD5) As String
Dim hCtx As Long
Dim hHash As Long
Dim lRes As Long
Dim lLen As Long
Dim lIdx As Long
Dim abData() As Byte

   ' Get default provider context handle
   lRes = CryptAcquireContext(hCtx, vbNullString, _
           vbNullString, PROV_RSA_FULL, 0)

   If lRes <> 0 Then

      ' Create the hash
      lRes = CryptCreateHash(hCtx, Algorithm, 0, 0, hHash)

      If lRes <> 0 Then

         ' Hash the string
         lRes = CryptHashData(hHash, ByVal Str, Len(Str), 0)

         If lRes <> 0 Then
            
            ' Get the hash lenght
            lRes = CryptGetHashParam(hHash, HP_HASHSIZE, lLen, 4, 0)

            If lRes <> 0 Then

                ' Initialize the buffer
                ReDim abData(0 To lLen - 1)

                ' Get the hash value
                lRes = CryptGetHashParam(hHash, HP_HASHVAL, abData(0), lLen, 0)

                If lRes <> 0 Then

                    ' Convert value to hex string
                    For lIdx = 0 To UBound(abData)
                        HashString = HashString & _
                                     Right$("0" & Hex$(abData(lIdx)), 2)
                    Next

                End If

            End If

         End If

         ' Release the hash handle
         CryptDestroyHash hHash

      End If
      
   End If

   ' Release the provider context
   CryptReleaseContext hCtx, 0

   ' Raise an error if lRes = 0
   If lRes = 0 Then Err.Raise Err.LastDllError

End Function