' Digital signature creation example for VB
' Perform processing in 8K (8192 byte) chunks. 

Const CHUNKSIZE = 8192 

Dim xSign As New XceedSigning ' Instantiate the object
Call xSign.License( "your license key" ) 

Dim lOffSet As Long ' We manage the read offset in the file
Dim lFileSize As Long
Dim lBytesRead As Long
Dim vaSignature As Variant ' Here is where the signature will go 

' Set the signing method type 
Set xSign.SigningMethod = New XceedRSASigningMethod 

On Error Resume Next 

' The following call to SetRandomKeyPair would, in the real world,
' be replaced by the assignment of a Private Key to the
' PrivateKey property. 

Call xSign.SigningMethod.SetRandomKeyPair(512, Empty) 

' Set up to read from the file 

lOffSet = 0 ' We must track the current offset
lFileSize = FileLen("c:\temp\source.txt") 

While lOffSet < lFileSize
  ' bEndOfData will be true if the current offset + CHUNKSIZE exceeds 
  ' the end of the file.  
  lBytesRead = xSign.ReadFile("c:\temp\source.txt", lOffSet, CHUNKSIZE, efpSign, _
                              (lOffSet + CHUNKSIZE >= lFileSize)) 

  lOffSet = lOffSet + lBytesRead 
Wend 

If Err.Number = 0 Then
  Call MsgBox("Finished Signing file to memory.") 
  vaSignature = xSign.SigningMethod.Signature 

  ' Do something with the signature... 
  lOffSet = 0 
  While lOffSet < lFileSize And Err.Number = 0 
    ' bEndOfData will be true if the current offset + CHUNKSIZE exceeds 
    ' the end of the file. 

    lBytesRead = xSign.ReadFile("c:\temp\source.txt", lOffSet, CHUNKSIZE, efpVerify, _
                                (lOffSet + CHUNKSIZE >= lFileSize)) 

    lOffSet = lOffSet + lBytesRead 
  Wend  

  If Err.Number = 0 Then 
    Call MsgBox("Data verified successfully") 
  Else 
    If Err.Number = eerVerifyFailed Then 
      Call MsgBox("Verification of signature failed") 
    Else 
      Call MsgBox("Error 0x" & Hex(Err.Number) & " " & Err.Description) 
    End If 
  End If 
Else
  Call MsgBox("Error 0x" & Hex(Err.Number) & " " & Err.Description) 
End If 

On Error GoTo 0 

Set xSign = Nothing