Imports System.IO
' And System.Security.Cryptography for Hashes : MD5, SHA1, SHA256, ...
Imports System.Security
Imports System.Security.Cryptography
Module Hash
    Function hash_generator(ByVal hash_type As String, ByVal file_name As String)

        ' We declare the variable : hash
        Dim hash
        If hash_type.ToLower = "sha256" Then
            ' Initializes a SHA-256 hash object
            hash = SHA256.Create()
        Else
            MsgBox("Unknown type of hash : " & hash_type, MsgBoxStyle.Critical)
            Return False
        End If

        ' We declare a variable to be an array of bytes
        Dim hashValue() As Byte

        ' We create a FileStream for the file passed as a parameter
        Dim fileStream As FileStream = File.OpenRead(file_name)
        ' We position the cursor at the beginning of stream
        fileStream.Position = 0
        ' We calculate the hash of the file
        hashValue = hash.ComputeHash(fileStream)
        ' The array of bytes is converted into hexadecimal before it can be read easily
        Dim hash_hex = PrintByteArray(hashValue)

        ' We close the open file
        fileStream.Close()

        ' The hash is returned
        Return hash_hex

    End Function
    Public Function PrintByteArray(ByVal array() As Byte)

        Dim hex_value As String = ""

        ' We traverse the array of bytes
        Dim i As Integer
        For i = 0 To array.Length - 1

            ' We convert each byte in hexadecimal
            hex_value += array(i).ToString("X2")

        Next i

        ' We return the string in lowercase
        Return hex_value.ToLower

    End Function
    Function sha_256(ByVal file_name As String)
        Return hash_generator("sha256", file_name)
    End Function
End Module