md5 hash of a whole file RESOLVED

[Usul]

Well, how can I get the md5 hashvalue of a whole file?

I only found how to encrypt strings in the web, but nothing about whole files.

I tried it myself, but the result is not the same as when I use a freeware programm (and I assume the error is in MY code):

    Private Sub testHash(ByVal filepath As System.String)
        Dim hashvalue As String
        Dim inputStream As FileStream
        inputStream = File.OpenRead(filepath)
        Dim tmpSource(1024) As Byte
        Dim tmpHash() As Byte
        inputStream.Read(tmpSource, 0, tmpSource.Length)

        tmpHash = New MD5CryptoServiceProvider().ComputeHash(tmpSource)
        Dim i As Integer
        Dim sOutput As New StringBuilder(tmpHash.Length)
        For i = 0 To tmpHash.Length - 1
            sOutput.Append(tmpHash(i).ToString("X2"))
        Next
        hashvalue = sOutput.ToString()
        inputStream.Close()

        MessageBox.Show(hashvalue)
    End Sub

any help appreciated,

thanx

Usul

[pax]

Hi. I have absolutely no idea about MD5 hashes, but there is one thing that strikes me as odd about your code.

it's the "Dim tmpSource(1024) As Byte" line.
This makes an array of 1025 bytes. I would imagine that it should be 1024, hence the line should be : "Dim tmpSource(1023) As Byte"

As I said, I have no idea about MD5, but I just thought it to be logical to use 1024 bytes and not 1025.

Hope it helps...If not then please ignore it

[Usul]

no it doesnt matter, the array is only supposed to be big enough to contain the file.

[pax]

Ok, I see.

I have another idea though...

Could it be because of old data in the array when reaching the end of the file?

Imagine you have an array of 10 containing value 1,2,3,4,5,6,7,8,9,10.

If the file if 15 bytes long the last read would return only 5 bytes.

So the array would be a,b,c,d,e,6,7,8,9,10.

So then 6-10 would be computed again.

I think the "inputStream.Read" method returns the number of bytes actually read. I think you have make a new array matching the size or at least clear the old array to 0's first.

Another way may be to make the array big enough to contain the whole file in one go, or only read 1 byte at the time.

[Usul]

thanx for helping.

but i found a solution now. took me hours, but it finally works.

Private Function GenerateHash(ByVal thepath As System.String, ByVal thefile As System.String)
        Dim filepath As System.String
        filepath = thepath + thefile
        Dim hashvalue As String
        Dim inputStream As FileStream
        inputStream = File.OpenRead(filepath)
        Dim tmpHash() As Byte
 
        tmpHash = New MD5CryptoServiceProvider().ComputeHash(inputStream)
        Dim i As Integer
        Dim sOutput As New StringBuilder(tmpHash.Length)
        For i = 0 To tmpHash.Length - 1
            sOutput.Append(tmpHash(i).ToString("X2"))
        Next
        hashvalue = sOutput.ToString()
        hashvalue = hashvalue.ToLower()
        inputStream.Close()
 
        Return hashvalue
    End Function

[pax]

Cool.

So you just had to put the stream directly into Compute function instead of an array. I think that is due to the reason I explained above, although I can't be sure.

[Usul]

i think you are right. it most likely is the problem you described.

[PT Exorcist]

There is a code in C# in codeproject that creates md5 hashes of streams/strings. Just search for it