# 经典加密算法在VB中的实现：Base64

2010-03-30

Public key(1 To 3) As Long　　Private Const base64 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrst　　uvwxyz0123456789+/"　　Public Sub GenKey()　　Dim d As Long, phi As Long, e As Long　　Dim m As Long, x As Long, q

Public key(1 To 3) As Long
Private Const base64 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrst
uvwxyz0123456789+/"
Public Sub GenKey()
Dim d As Long, phi As Long, e As Long
Dim m As Long, x As Long, q As Long
Dim p As Long
Randomize
On Error GoTo top
top:
p = Rnd * 1000 1
If IsPrime(p) = False Then GoTo top
Sel_q:
q = Rnd * 1000 1
If IsPrime(q) = False Then GoTo Sel_q
n = p * q 1
phi = (p - 1) * (q - 1) 1
d = Rnd * n 1
If d = 0 Or n = 0 Or d = 1 Then GoTo top
e = Euler(phi, d)
If e = 0 Or e = 1 Then GoTo top
x = Mult(255, e, n)
If Not Mult(x, d, n) = 255 Then
DoEvents
GoTo top
ElseIf Mult(x, d, n) = 255 Then
key(1) = e
key(2) = d
key(3) = n
End If
End Sub
Private Function Euler(ByVal a As Long, ByVal b As Long) As Long
On Error GoTo error2
r1 = a: r = b
p1 = 0: p = 1
q1 = 2: q = 0
n = -1
Do Until r = 0
r2 = r1: r1 = r
p2 = p1: p1 = p
q2 = q1: q1 = q
n = n + 1
r = r2 Mod r1
c = r2 r1
p = (c * p1) + p2
q = (c * q1) + q2
Loop
s = (b * p1) - (a * q1)
If s > 0 Then
x = p1
Else
x = (0 - p1) + a
End If
Euler = x
Exit Function

error2:
Euler = 0
End Function
Private Function Mult(ByVal x As Long, ByVal p As Long, ByVal m As Lon
g) As Long
y = 1
On Error GoTo error1
Do While p > 0
Do While (p / 2) = (p 2)
x = (x * x) Mod m
p = p / 2
Loop
y = (x * y) Mod m
p = p - 1
Loop
Mult = y
Exit Function
error1:
y = 0
End Function
Private Function IsPrime(lngNumber As Long) As Boolean
Dim lngCount As Long
Dim lngSqr As Long
Dim x As Long
lngSqr = Sqr(lngNumber) ’ get the int square root
If lngNumber < 2 Then
IsPrime = False
Exit Function
End If
lngCount = 2
IsPrime = True
If lngNumber Mod lngCount = 0& Then
IsPrime = False
Exit Function
End If
lngCount = 3
For x& = lngCount To lngSqr Step 2
If lngNumber Mod x& = 0 Then
IsPrime = False
Exit Function
End If
Next
End FunctionPrivate Function Base64_Encode(DecryptedText As String) As String
Dim c1, c2, c3 As Integer
Dim w1 As Integer
Dim w2 As Integer
Dim w3 As Integer
Dim w4 As Integer
Dim n As Integer
Dim retry As String
For n = 1 To Len(DecryptedText) Step 3
c1 = Asc(Mid\$(DecryptedText, n, 1))
c2 = Asc(Mid\$(DecryptedText, n + 1, 1) + Chr\$(0))
c3 = Asc(Mid\$(DecryptedText, n + 2, 1) + Chr\$(0))
w1 = Int(c1 / 4)
w2 = (c1 And 3) * 16 + Int(c2 / 16)
If Len(DecryptedText) >= n + 1 Then w3 = (c2 And 15) * 4 + Int(c
3 / 64) Else w3 = -1
If Len(DecryptedText) >= n + 2 Then w4 = c3 And 63 Else w4 = -1
retry = retry + mimeencode(w1) + mimeencode(w2) + mimeencode(w3)
+ mimeencode(w4)
Next
Base64_Encode = retry
End Function
Private Function Base64_Decode(a As String) As String
Dim w1 As Integer
Dim w2 As Integer
Dim w3 As Integer
Dim w4 As Integer
Dim n As Integer
Dim retry As String
For n = 1 To Len(a) Step 4
w1 = mimedecode(Mid\$(a, n, 1))
w2 = mimedecode(Mid\$(a, n + 1, 1))
w3 = mimedecode(Mid\$(a, n + 2, 1))
w4 = mimedecode(Mid\$(a, n + 3, 1))
If w2 >= 0 Then retry = retry + Chr\$(((w1 * 4 + Int(w2 / 16)) An
d 255))
If w3 >= 0 Then retry = retry + Chr\$(((w2 * 16 + Int(w3 / 4)) An
d 255))
If w4 >= 0 Then retry = retry + Chr\$(((w3 * 64 + w4) And 255))
Next
Base64_Decode = retry
End Function
Private Function mimeencode(w As Integer) As String
If w >= 0 Then mimeencode = Mid\$(base64, w + 1, 1) Else mimeencode
= ""
End Function
Private Function mimedecode(a As String) As Integer
If Len(a) = 0 Then mimedecode = -1: Exit Function
mimedecode = InStr(base64, a) - 1
End Function
Public Function Encode(ByVal Inp As String, ByVal e As Long, ByVal n A
s Long) As String
Dim s As String
s = ""
m = Inp
If m = "" Then Exit Function
s = Mult(CLng(Asc(Mid(m, 1, 1))), e, n)
For i = 2 To Len(m)
s = s & "+" & Mult(CLng(Asc(Mid(m, i, 1))), e, n)
Next i
Encode = Base64_Encode(s)
End Function
Public Function Decode(ByVal Inp As String, ByVal d As Long, ByVal n A
s Long) As String
St = ""
ind = Base64_Decode(Inp)
For i = 1 To Len(ind)
nxt = InStr(i, ind, "+")
If Not nxt = 0 Then
tok = Val(Mid(ind, i, nxt))
Else
tok = Val(Mid(ind, i))
End If
St = St + Chr(Mult(CLng(tok), d, n))
If Not nxt = 0 Then
i = nxt
Else
i = Len(ind)
End If
Next i
Decode = St
End Function