Dim s As String = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklnmopqrstuvwxz-" 'ce qui sera generer (les caracteres)
Dim r As New Random
Dim sb As New StringBuilder
For i As Integer = 1 To 20 '20 est le nombre de caracteres
Dim idx As Integer = r.Next(0, 35)
sb.Append(s.Substring(idx, 1))
Next
TextBox1.Text = sb.ToString()
End Sub