Hash with MD5 in VB.NET

Question 1

It is important to note that MD5 is no longer considered a good way to hash data you wish to protect. See wikipedia for a discussion of the vulnerabilities.

See this answer for hashing using SHA.

For passwords, you'd save the hash of the user's PW to the DB. Because it is one-way (you cannot easily get the original value back from the hash), this prevents someone like a janitor or customer service rep from being able to see the actual passwords in the database.

Imports System.Security.Cryptography
Imports System.Text

Shared Function GetHash(theInput As String) As String

    Using hasher As MD5 = MD5.Create()    ' create hash object

        ' Convert to byte array and get hash
        Dim dbytes As Byte() = 
             hasher.ComputeHash(Encoding.UTF8.GetBytes(theInput))

        ' sb to create string from bytes
        Dim sBuilder As New StringBuilder()

        ' convert byte data to hex string
        For n As Integer = 0 To dbytes.Length - 1
            sBuilder.Append(dbytes(n).ToString("X2"))
        Next n

        Return sBuilder.ToString()
    End Using

End Function

Depending on how you want to save it, rather than a using StringBuilder to create a hex string, you can use Convert.ToBase64String():

Return Convert.ToBase64String(dbytes)
' MyWeakPassword hashed:
'     to hex: DB28F1BE20A407398171295DD0D191E2
'  to Base64: 2yjxviCkBzmBcSld0NGR4g==

Hashing should be done with salt. This is data added to the hash to make the result less predictable (there are dictionaries of the hashed results of common PW such as "password"; salt changes the outcome):

Shared Function GetHash(theInput As String, theSalt As String) As String
...
      hasher.ComputeHash(Encoding.UTF8.GetBytes(theInput & theSalt))

Salt should be created using the Cryptographic random number generator as shown in the SHA Version. Convert the salt to text (hex or Base64) then combine with the PW to get the PW hash.

To check/compare a user's entry, simply hash the input and compare it to the hash stored in the database, using the same Salt (which means the Salt needs to be saved):

 Shared Function CheckHash(hashedStr As String, newInput As String) As Boolean
    ' get the hash value of user input: 
    Dim newHash  As String = GetHash(newInput & dbSalt) 

    ' return comparison
    Return String.Compare(newHash, hashedStr, InvariantCultureIgnoreCase)
 End Function

As written, the GetHash function is intended to be used from something like a CryptoTools Class. Since it is Shared/Static the class need not be instanced:

  thisHash = CryptoTools.GetHash(strToHash)

Note: Hashing is case sensitive, so foobar will result in a different hash than FooBar or FOOBAR. To create a case insensitive system, convert the original string (such as a password) to lowercase before you compute the MD5 hash value to be saved, and do the same for the value they later enter:

' ToLowerInvariant allows for foreign char sets
Dim str As String = PWTextBox.Text.ToLowerInvariant

If CheckHash(dbHashedValue, str) Then
    ' okie dokie
Else
    ' failed
End If

Question 2

MD5 Convertion

Dim [source] As String = password_text_box.text 
Using md5Hash As MD5 = MD5.Create()
Dim hash As String = GetMd5Hash(md5Hash, source)

2, Insert Name and hash into database

3, Validation

During login take MD5 of password again run sql query

Select name,password from table where Login ='" & username & "' and Password ='" & md5(user input pass) & "'

if dreader returns value , then valid login else invalid login

Question 3

   Private Function GetHash(strToHash As String) As String

    Dim md5Obj As New System.Security.Cryptography.MD5CryptoServiceProvider
    Dim bytesToHash() As Byte = System.Text.Encoding.ASCII.GetBytes(strToHash)

    bytesToHash = md5Obj.ComputeHash(bytesToHash)
    Dim strResult As New StringBuilder

    For Each b As Byte In bytesToHash
        strResult.Append(b.ToString("x2"))
    Next

    Return strResult.ToString

End Function

Question 4

This would be my solution:

Public Sub _Enkripsi()

    Dim _DES As New TripleDESCryptoServiceProvider()
    Dim _HashMD5 As New MD5CryptoServiceProvider()

    _DES.Key = _HashMD5.ComputeHash(System.Text.ASCIIEncoding.ASCII.GetBytes(PasswordTextBox.Text))
    _DES.Mode = CipherMode.ECB
    Dim _DESEncrypt As ICryptoTransform = _DES.CreateEncryptor()
    Dim _Buffer As Byte() = System.Text.ASCIIEncoding.ASCII.GetBytes(PasswordTextBox.Text)
    _Password = Convert.ToBase64String(_DESEncrypt.TransformFinalBlock(_Buffer, 0, _Buffer.Length))

End Sub

Question 5

Convert String to MD5 Function for Visual Studio Basic 2022

Imports System.Security.Cryptography

Imports System.Text


Function CovertToMD5(retVal As String) As String
    Using MD5 = System.Security.Cryptography.MD5.Create()
        Return BitConverter.ToString(MD5.ComputeHash(Encoding.Default.GetBytes(retVal))).Replace("-", String.Empty)
    End Using
End Function