Originally Posted by abu taher

Try it.

Originally Posted by Teme64

There's never a 100% secure solution.

First, do not store password in plain text. Use some hash function to calculate hashed value of the password and store this hashed value. Some methods are MD5, SHA1 or simple CRC32 etc. You'll find sample code with Google. So when the user gives his/her password, you calculate hash and compare calculated hash with the stored hash value, not the password itself.

Second, where to store hashed passwords? Do you use some database to store them? If you have only one user who's allowed to access, you can store hashed password in registry. Of course, it can be removed from there. Another solution, and quite feasible today, is to store it in a file in USB memory stick. Then user requires both USB stick and the USB stick must contain hashed password in a file.

I won't give here the actual code for password prompt dialog and password change dialog. They are quite straightforward to implement, but I'll give help with them if needed.

Originally Posted by Teme64

Ok. I've ripped this partly from my app which is written in VB.NET not VB6 and the rest is sort of "pseudo code". So, you'll need in VB6 a) MD5-funtion and b) a way to convert string to bytes. You'll find VB6 code for that with Google (I did some 10 yrs ago

First, user enters initial password:

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VB.NET Syntax (Toggle Plain Text)

Imports System.Security.Cryptography
 
Private Sub CalculateMD5(ByVal BytesIn() As Byte, ByRef ResultMD5() As Byte)
  '
  ' Calculate MD5 for bytes
  Dim ProvMD5 As MD5
 
  Try
    ProvMD5 = MD5CryptoServiceProvider.Create()
    ProvMD5.Initialize()
    ResultMD5 = ProvMD5.ComputeHash(BytesIn)
    ProvMD5.Clear()
  Catch ex As Exception
    ' Handle error
  End Try
 
End Sub
 
Private Function MD5ToString(ByVal BytesIn() As Byte) As String
  '
  ' Return MD5 as a hex string
  Dim UBits As Integer
  Dim LBits As Integer
  Dim TempStr As String
  Dim i As Integer
 
  Try
    TempStr = ""
    For i = 0 To BytesIn.GetUpperBound(0)
      UBits = (BytesIn(i) And 240) >> 4
      LBits = (BytesIn(i) And 15)
      TempStr = TempStr & String.Format("{0:x}", UBits)
      TempStr = TempStr & String.Format("{0:x}", LBits)
    Next i
    Return TempStr
  Catch ex As Exception
    ' Handle error
    Return ""
  End Try
 
End Function

Imports System.Security.Cryptography Private Sub CalculateMD5(ByVal BytesIn() As Byte, ByRef ResultMD5() As Byte) ' ' Calculate MD5 for bytes Dim ProvMD5 As MD5 Try ProvMD5 = MD5CryptoServiceProvider.Create() ProvMD5.Initialize() ResultMD5 = ProvMD5.ComputeHash(BytesIn) ProvMD5.Clear() Catch ex As Exception ' Handle error End Try End Sub Private Function MD5ToString(ByVal BytesIn() As Byte) As String ' ' Return MD5 as a hex string Dim UBits As Integer Dim LBits As Integer Dim TempStr As String Dim i As Integer Try TempStr = "" For i = 0 To BytesIn.GetUpperBound(0) UBits = (BytesIn(i) And 240) >> 4 LBits = (BytesIn(i) And 15) TempStr = TempStr & String.Format("{0:x}", UBits) TempStr = TempStr & String.Format("{0:x}", LBits) Next i Return TempStr Catch ex As Exception ' Handle error Return "" End Try End Function

Get a password from the user, calculate hash and store hash.

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VB.NET Syntax (Toggle Plain Text)

Imports System.Text
 
Dim StringData As String
Dim ByteData() as Byte
Dim ResultHash() As Byte
Dim HashedPwString As String
 
' Get password to StringData and convert to bytes
ByteData = Encoding.Default.GetBytes(StringData)
' Hash it
CalculateMD5(ByteData, ResultHash)
' Make a string from bytes, you could use also Encoding.Default.GetString()
HashedPwString = MD5ToString(ResultHash)
' Now, store HashedPwString to somewhere!

Imports System.Text Dim StringData As String Dim ByteData() as Byte Dim ResultHash() As Byte Dim HashedPwString As String ' Get password to StringData and convert to bytes ByteData = Encoding.Default.GetBytes(StringData) ' Hash it CalculateMD5(ByteData, ResultHash) ' Make a string from bytes, you could use also Encoding.Default.GetString() HashedPwString = MD5ToString(ResultHash) ' Now, store HashedPwString to somewhere!

How to compare hashes:
Use the same code as above to (prompt password) and calculate HashedPwString from it. Then compare:

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Visual Basic 4 / 5 / 6 Syntax (Toggle Plain Text)

Dim StoredHash As String
' Read StoredHash from somewhere
If HashedPwString = StoredHash Then
  ' Yes the passwords are the same
Else
  ' No match, kindly tell the user to re-enter password. Or just kick him out
End If

Dim StoredHash As String ' Read StoredHash from somewhere If HashedPwString = StoredHash Then ' Yes the passwords are the same Else ' No match, kindly tell the user to re-enter password. Or just kick him out End If

Here's a one MD5 code (in VB6) http://www.di-mgt.com.au/crypto.html#MD5 but I haven't tried it myself. That code seems(?) to get strings as parameter so you do not need string->byte->string conversions. Just rewrite CalculateMD5() with the VB6 code (from that link).

BTW. If you use VB.NET, you can change MD5 -> SHA1 and get a slightly better hashes.