Community articleHash function
Added by IBM contributorIBM on August 15, 2011
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No abstract provided.


This function hashes a message using the hashing algorithm of your choice.


   Function Hash(
      theMessage As Variant)


Table 1. hash parameters
theMessageVariantThe message you want to hash.
Note that the function expects the hashed secret to be a single-byte binary array. Using a double-byte binary array will produce an incorrect result.


A hashed message, or throws an exception if an error occurs.


The following function validates an HMAC signature using a hashed secret. First, the function uses DereferenceEx and GetLiteralByRefEx to locate the signature item in a form. It then uses GetEngineCertificateList and GetDataByPath to locate a server signing certificate. Next, it uses GetSignature and GetDataByPath to get the signer's common name and LookupHashAlgorith and Hashto create a hashed secret. Finally, it uses ValidateHMACWithHashedSecret to determine if the HMAC signature is valid, and returns "Valid" or "Invalid", as appropriate.
Note that this example also relies on a second function called StringToBinary. This function converts a string to a single-byte binary array, which is required for the hash function. This prevents COM from converting the string to a double-byte array before hashing it, which would produce an incorrect result.
   Function ValidateHMACSigHashed(Form)
      Dim SigObject, XFDL, HashObject, SecurityManager  ' objects
      Dim TheCerts  ' CertificateList
      Dim Cert, SigningCert  ' ICertificate
      Dim SignerName, SharedSecret, HashedSecret, CommonName, _
         SigItemRef  ' Strings
      Dim Validation  ' Integer
      Dim TempNode, SigNode  ' IFormNodeP
      Set TempNode = Form
      ' Get the SignatureButton node
      Set TempNode = Form.DereferenceEx(vbNullString, _
         "PAGE1.HMACSignatureButton", 0, UFL_ITEM_REFERENCE, Nothing)
      ' Get the name of the signature item
      SigItemRef = TempNode.GetLiteralByRefEx(vbNullString, "signature", _
         0, vbNullString, Nothing)
      ' Get the signature item node
      Set SigNode = TempNode.DereferenceEx(vbNullString, SigItemRef, 0, _
         UFL_ITEM_REFERENCE, Nothing)
      ' Get available server certificates for Generic RSA signing
      Set XFDL = CreateObject("PureEdge.xfdl_XFDL")
      Set TheCerts = XFDL.GetEngineCertificateList("Generic RSA", 1) 
         ' vbNull
      ' Locate the certificate that has a common name of "User1-CP.02.01".
      ' This is the certificate we will use when verifying the signature.
      For Each Cert in TheCerts
         CommonName = Cert.GetDataByPath("SigningCert: Subject: CN", _
            False, 1) ' vbNull
         If CommonName = "User1-CP.02.01" Then
            Set SigningCert = Cert
         End If
      ' Get the signature object from the signature node
      Set SigObject = SigNode.GetSignature
      ' Get the signer's name from the signature object
      SignerName = SigObject.GetDataByPath("SigningCert: Subject: CN", _
         False, 1) ' vbNull
      ' Include code that matches the signer's identity to a shared secret
      ' that is hashed, and sets SharedSecret to match. In most cases, this 
      ' would be a database lookup. For the purposes of this example, we will
      ' use the Hash function to assign a hashed value to HashedSecret.
      ' Get the Security Manager object
      Set SecurityManager = _
      ' Get the Hash object
      Set HashObject = SecurityManager.LookupHashAlgorithm("sha1")
      ' Set the Hashed secret. First convert the secret to a single-byte
      ' binary array, then hash the secret.
      SharedSecret = StringToBinary("secret")      
      HashedSecret = HashObject.Hash(SharedSecret)
      ' Validate the signature
      Validation = SigNode.ValidateHMACWithHashedSecret(HashedSecret, _
         SigningCert, 1) ' vbNull
      ' Check the validation code and return either "Valid" or "Invalid"
      If Validation = UFL_DS_OK Then
         ValidateHMACSigHashed = "Valid"
         ValidateHMACSigHashed = "Invalid"
      End If
   End Function
   ' The following function is required to convert a string to a single-byte '  
   ' binary array before hashing that string. This prevents COM from converting
   ' the string to a multi-byte format, which would produce an incorrect hash.
Function StringToBinary(String)
      Dim Counter, Binary
      For Counter = 1 to len(String)
         Binary = Binary & ChrB(Asc(Mid(String, Counter, 1)))
      StringToBinary = Binary
   End Function

Parent topic:
Hash functions