专家教你如何用VB编写一个加密软件

Function ByteToBin(m As Byte) As String   ' 将字节型数据转换成八位二进制字符串
  Dim c$
  c$ = ""
  Do While m <> 0
    r = m Mod 2
    m = m \ 2
    c$ = r & c$
  Loop
  c$ = Right("00000000" & c$, 8)
  ByteToBin = c$
End Function
Function Reverse(m As String) As String     ' 将八位二进制字符串颠倒顺序
  Dim i%, x$
  x = ""
  For i = 1 To 8
    x = Mid(m, i, 1) & x
  Next i
  Reverse = x
End Function
Function BinToByte(m As String) As Byte     ' 将八位二进制串转换成十进制
  Dim x As String * 1, y%, z%
  z = 0
  For i = 1 To 8
    x = Mid(m, i, 1)
    y = x * 2 ^ (8 - i)
    z = z + y
  Next i
  BinToByte = z
End Function
Private Sub Command1_Click()
  Dim x As Byte, i%, fname$
  fname = InputBox("请输入要加密的文件名！注意加上路径名：")
  If Dir(fname) = "" Then
    MsgBox "文件不存在！"
    Exit Sub
  End If
  Open fname For Binary As #1         ' 以二进制访问模式打开待加密文件
  For i = 1 To LOF(1)               ' LOF函数是求文件长度的内部函数
    Get #1, i, x                 ' 取出第i个字节
    x = BinToByte(Reverse(ByteToBin(x))) ' 这里调用了三个自定义函数
    Put #1, i, x                 ' 将加密后的这个字节写回到文件原位置
  Next i
  Close
  MsgBox "任务完成！"
End Sub