IMEI Validation Technique (VB.NET)

Hi ,

I would like to share a simple Technique to check for Valid IMEI Number.

For those who dont know what IMEI is it is International Mobile Equipment Identity Code is a unique 15 Digit number which is usually found printed on the back side of the GSM/CDMA mobile phones battery.

The Logic behind identifying a correct IMEI Code is very simple.

First Ill show you the Structure of the Code and then Then the Automated way to check it.

AAAAAAAA – BBBBBB – C (This is the Structure)

AAAAAAAA = Type Allocation Code – The Type Allocation Code is an 8-digit number that identifies a particular model of wireless telephone for use on a GSM wireless network.
BBBBBB – Serial sequence of the model

And the most Important of All

C -The last number of the IMEI is a check digit calculated using the Luhn algorithm.
The check digit is validated in 3 steps:

1. Starting from the right, double a digit every second digits (e.g., 8 → 16).
2. Sum the digits (e.g., 16 → 1 + 6).
3. Check if the sum is divisible by 10.

One can calculate the IMEI by choosing the check digit that would give a sum divisible by 10. For the example IMEI 352048021523553,

[TABLE]
[TR]
[TD]IMEI[/TD]
[TD] 3[/TD]
[TD]5[/TD]
[TD]2[/TD]
[TD]0[/TD]
[TD]4[/TD]
[TD] 8[/TD]
[TD]0[/TD]
[TD]2[/TD]
[TD]1[/TD]
[TD]5[/TD]
[TD]2[/TD]
[TD]3[/TD]
[TD]5[/TD]
[TD]5[/TD]
[TD] ?[/TD]
[/TR]
[TR]
[TD]Double Every Second Digit [/TD]
[TD] 3[/TD]
[TD]10[/TD]
[TD]2[/TD]
[TD]0[/TD]
[TD]4[/TD]
[TD]16[/TD]
[TD]0[/TD]
[TD]4[/TD]
[TD]1[/TD]
[TD]10[/TD]
[TD]2[/TD]
[TD]6[/TD]
[TD]5[/TD]
[TD]10[/TD]
[TD] ?[/TD]
[/TR]
[TR]
[TD]Sum digits[/TD]
[TD="colspan: 15"]3+1+0+2+0+4+1+6+0+4+1+1+0+2+6+5+1+0 = 37[/TD]
[/TR]
[/TABLE]

To make the sum divisible by 10, we set ? = 3, so the IMEI is .352048021523553

Below is the Code in VB.NET you can use it in ASP.NET also to check a Valid IMEI number

Private Sub TextBox1_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs)
            If TextBox1.Text.Length = 15 Then
                          Dim IMEI As String = TextBox1.Text 
                          Dim cnt As Integer = 0 
                          Dim nw As String = “”
                   For Each c As Char In
                          IMEIcnt += 1
                            If cnt Mod 2 <> 0 Then
                                  nw += c
                            Else
                                 Dim d As Integer = Integer.Parse(c) * 2nw += d.ToString()
                            End If
                  Next
Dim tot As Integer = 0 
For Each ch As Char In nw.Remove(nw.Length – 1, 1)
          tot +=Integer.Parse(ch)
Next
Dim chDigit As Integer = 10 – (tot Mod 10)  
         If chDigit = Integer.Parse(IMEI(IMEI.Length – 1)) Then
                  MsgBox(“Valid”) 
          Else
                  MsgBox(“Invalid”) 
         End If
    End If
End Sub

Code (markup):

For it to work in ASP.NET Put the code in a Button Click..

Hope this helps..

The original Post is on my Blog (Few Months Back)
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