by Gregg Housh (10 Submissions)
Category: String Manipulation
Compatability: Visual Basic 3.0
Difficulty: Intermediate
Date Added: Wed 3rd February 2021
Rating: 
(5 Votes)
This code will take a range (lower and upper), and output a string of random characters (0-9, A-Z, a-z). I use this to generate a key for encryption, during the key negotiation phase of a connection to an encrypted server.
Usage is simple:
Dim sKey as string
sKey = GenerateKey(10,100)
' this code generates a key with a length between
' 10 and 100 characters.
Inputs
iLower: Lowest possible length for the string
iUpper: Maximum length for the string
Code Returns
Returns a string.
VBcoders' Credit goes to these people for code I
' borrowed/modified:
' Kevin Lawrence - non-repeating random
' number generator
' VBPJ - GenerateRandomNumberInRange
' (modified by me, from a shuffle routine in VBPJ)
Public Function GenerateKey(ByVal iLower As Integer, ByVal iUpper As Integer) As String
Dim sKey As String
Dim sChar As String
Dim iLen As Integer
Dim iLoop As Integer
' dont need keys TOO big ...
iLen = GetRandomNumberInRange(iLower, iUpper)
For iLoop = 1 To iLen
' dont include quotes
Retry:
Do
sChar = Chr(GetRandomNumber())
Loop While sChar = Chr(34)
' make sure its 0-9, A-Z, or a-z
If Not IsValidChar(sChar) Then
GoTo Retry:
Else
sKey = sKey & sChar
End If
Next iLoop
GenerateKey = sKey
End Function
Private Function IsValidChar(ByVal sChar As String) As Boolean
Dim btoggle As Boolean
If Asc(sChar) >= 48 And Asc(sChar) <= 57 Then
'valid #
btoggle = True
ElseIf Asc(sChar) >= 65 And Asc(sChar) <= 90 Then
'valid uppercase character
btoggle = True
ElseIf Asc(sChar) >= 97 And Asc(sChar) <= 122 Then
btoggle = True
Else
btoggle = False
End If
IsValidChar = btoggle
End Function
Public Function GetRandomNumberInRange(Lower As Integer, Upper As Integer) As Integer
Static PrimeFactor(10) As Integer
Static a As Integer
Static c As Integer
Static b As Integer
Static s As Long
Static n As Integer
Static n1 As Integer
Dim i As Integer
Dim j As Integer
Dim K As Integer
Dim m As Integer
Dim t As Boolean
If (n <> Upper - Lower + 1) Then
n = Upper - Lower + 1
i = 0
n1 = n
K = 2
Do While K <= n1
If (n1 Mod K = 0) Then
If (i = 0 Or PrimeFactor(i) <> K) Then
i = i + 1
PrimeFactor(i) = K
End If
n1 = n1 / K
Else
K = K + 1
End If
Loop
b = 1
For j = 1 To i
b = b * PrimeFactor(j)
Next j
If n Mod 4 = 0 Then b = b * 2
a = b + 1
c = Int(n * 0.66)
t = True
Do While t
t = False
For j = 1 To i
If ((c Mod PrimeFactor(j) = 0) Or (c Mod a = 0)) Then t = True
Next j
If t Then c = c - 1
Loop
Randomize
s = Rnd(n)
End If
s = (a * s + c) Mod n
GetRandomNumberInRange = s + Lower
End Function
Public Function GetRandomNumber() As Integer
Dim a(122) ' Sets the maximum number To pick
Dim b(122) ' Will be the list of new numbers (same as DIM above)
Dim ChosenNumber As Integer
Dim MaxNumber As Integer
Dim seq As Integer
'Set the original array
MaxNumber = 122 ' Must equal the Dim above
For seq = 0 To MaxNumber
a(seq) = seq
Next seq
'Main Loop (mix em all up)
Randomize (Timer)
For seq = MaxNumber To 0 Step -1
ChosenNumber = Int(seq * Rnd)
b(MaxNumber - seq) = a(ChosenNumber)
a(ChosenNumber) = a(seq)
Next seq
' return a random number from a random position in B()
GetRandomNumber = b(GetRandomNumberInRange(1, 122))
End Function
