How to hash (MD5 or SHA1) a file with VB.NET

Posted on 2010-09-13
Last Modified: 2012-05-10
Hi experts..
I have a VB.NET application which imports a few csv files into a database nightly..
I need to ascertain if the file has changed from the previous nights import before I decide to import it or not.

I thought the easiest way would be to hash the file and store this hash in a table.
Then, each subsequent nightly import, I would simply hash the file, compare it with the hash of the file uploaded the previous night, if the hash's match, do nothing, if the hash's are different, perform the import..

So, can anyone poiont me in the right direction for hashing a file with VB.NET please??

Thanks in advance.

Question by:jcm4101
  • 3
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LVL 29

Accepted Solution

nffvrxqgrcfqvvc earned 500 total points
ID: 33668882
You can use HashAlgorithm Class, I wrote this class for when I need to calculate hash in either MD5 or SHA1 here you go.
The example defaults to MD5 but just change this line to use SHA1CryptoServiceProvider for SHA1 hash instead.
hashAlg = New MD5CryptoServiceProvider ' or New SHA1CryptoServiceProvider

Imports System.Security.Cryptography

Imports System.IO

Public Class FileChecksum

    Private Const BUF_SIZE As Integer = 65536

    ''' <summary>

    ''' Returns the file integrity checksum hash, otherwise an empty string.

    ''' </summary>

    Public Shared Function IntegrityCheck(ByVal filePath As String) As String

        Dim dataBuffer(BUF_SIZE - 1) As Byte

        Dim dataBufferDummy(BUF_SIZE - 1) As Byte

        Dim dataBytesRead As Integer = 0

        Dim hashResult As String = String.Empty

        Dim hashAlg As HashAlgorithm = Nothing

        Dim fs As FileStream = Nothing


            hashAlg = New MD5CryptoServiceProvider ' or New SHA1CryptoServiceProvider

            fs = New FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.None, BUF_SIZE)


                dataBytesRead = fs.Read(dataBuffer, 0, BUF_SIZE)

                hashAlg.TransformBlock(dataBuffer, 0, dataBytesRead, dataBufferDummy, 0)

            Loop Until dataBytesRead = 0

            hashAlg.TransformFinalBlock(dataBuffer, 0, 0)

            hashResult = BitConverter.ToString(hashAlg.Hash).Replace("-", "").ToLower

        Catch ex As IOException

            MsgBox(ex.Message, MsgBoxStyle.Critical, "IntegrityCheck")

        Catch ex As UnauthorizedAccessException

            MsgBox(ex.Message, MsgBoxStyle.Critical, "IntegrityCheck")


            If Not fs Is Nothing Then



                fs = Nothing

            End If

            If Not hashAlg Is Nothing Then

                hashAlg.Clear() 'Dispose()

                hashAlg = Nothing

            End If

        End Try

        Return hashResult

    End Function

End Class

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Author Closing Comment

ID: 33668977
Excellent work...
Thanks for the quick and complete solution.


Author Comment

ID: 33669031
Actually, I'm a bit confused...

What's the correct way to call this class??

LVL 29

Expert Comment

ID: 33669056
Whoops I forgot to show that part :(
It's basically just one shared method wrapped in class so it's similiar in respect to a module where you don't need to create an instance.
In the example below I used hashed the windows calculator on Windows 7: calc.exe MD5: 4884da7754823b44ccc2b2106f21146e


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Author Comment

ID: 33669084
Thanks  a lot..

Just sussed it out myself too  :-)

Greatly appreciated.


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