Question

我正在制作一个自定义加密应用程序并且我在更换部分停留。例如，我有字符串"AB12AB12"，我想加密它，以便每个A变为1，每个B a 2，每1个A和每2个B.如果一切正常，输出应该是12AB12AB但是这就是：

Private Sub Encrypt()
Dim str As String = "AB12AB12"
str = str.Replace("A", "1") 'now the output is "1B121B12"' 
str = str.Replace("B", "2") 'now the output is "12121212"'
str = str.Replace("1", "A") 'this is where it goes wrong, output is now "A2A2A2A2"
str = str.Replace("2", "B") 'now the output is "ABABABAB" and it should be "12AB12AB"
output = str
End Sub

问题是，使用此代码，您将继续更换所有内容，包括之前的替换。也许有一个选项可以同时替换每个角色，这样替换就不会被替换......

Answer 1

当您使用Replace进行替换时，您会得到一个包含已处理和未处理的混合字符的字符串，并且您无法区分它们。改为从头到尾处理字符串：

Private Function Encrypt(str as string) as String
  Dim source As String = "AB12"
  dim dest as string = "12AB"
  Dim result As New StringBuilder(str.Length)
  For Each c As Char In str
    result.Append(dest(source.IndexOf(c)))
  Next
  return result.ToString()
End Function

注意：我为该方法留下了名称Encrypt，尽管替换密码现在通常不被认为是加密。

Answer 2

这种失败的原因是因为如果你用"A" -> "1"修改str，那么转换回时也会使用这些'1'个字符：

"AB12AB12" --a>1--> "1B121B12"
"1B121B12" --b>2--> "12121212"
"12121212" --1>a--> "A2A2A2A2"
"A2A2A2A2" --2>b--> "ABABABAB"

基本上有两种方法可以做到这一点：

每个角色的字符
使用“临时字符”

<强>字符每字符

在这里，您每次迭代获取一个字符并将其转换为相应的值：

Private Sub Encrypt()
  Dim str As String = "AB12AB12"
  Dim fmc As Char() = {"A","B","1","2"}
  Dim toc As Char() = {"1","2","A","B"}
  Dim sb As New StringBuilder(str.Length)
  Dim i As Integer
  For i As Integer = 1 To str.Length-1
      sb.Append(fmc(Array.IndexOf(toc,GetChar(str,i))))
  Next
  output = sb.ToString()
End Sub

临时角色

如果你不知道'3'（或者会出现另一个角色，你可以简单说明）：

Private Sub Encrypt()
    Dim str As String = "AB12AB12"
    str = str.Replace("A", "3")
    str = str.Replace("1", "A")
    str = str.Replace("3", "1")
    str = str.Replace("B", "3")
    str = str.Replace("2", "B")
    str = str.Replace("3", "B")
    output = str
End Sub

然而，这会降低性能。

在旁注中，正如@HansPassant已经指出的那样，你最好不要设计自己的加密系统。例如，这可以通过频率分析轻松解决。

Answer 3

这里我提出了一种与你讨论不同的方法，检查可能性

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
            MsgBox(encrypt(plain_text.Text, replace_it.Text, replace_with.Text)) 
'display the result in the message box
  End Sub

其中plain_text.Text：输入文字
replace_it.Text：要替换的字符
replace_with.Text：该字符正在替换。

以下是用于执行加密的函数：

Public Function encrypt(ByVal str As String, ByVal frm As String, ByVal replace As String) As String
    Dim cipher As String
    cipher = ""
    For i As Integer = 0 To Len(str) - 1 'check each character separately
        If getbyte(str, i) = frm Then 
            cipher = cipher & replace 'replace the character if is same as the requested
        Else
            cipher = cipher & getbyte(str, i)
        End If
    Next
    Return cipher.ToString
End Function

函数获取字符串中的每个字符

Private Function getbyte(ByVal s As String, ByVal place As Integer) As String
    If place < Len(s) Then
        place = place + 1
        getbyte = Mid(s, place, 1)
    Else
        getbyte = ""
    End If
End Function

VB如何一次替换多个字符？

3 个答案: