关于BASE 24 ，BASE 64原理以及实现程序

关于BASE 24 ，BASE 64原理以及实现程序

来源 https://wangye.org/blog/archives/5/

可能很多人听说过Base64编码，很少有人听说过Base24编码，Base24编码主要应用在序列号生成上，其实基本的算法思想都是一样的，只是编码的模式有点变化。
Base64所对应的编码表是
ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=
共计64位。
而Base24所对应的编码表是
BCDFGHJKMPQRTVWXY2346789
共计24位，这里主要去掉了一些对于序列号来说不容易识别和容易混淆的字符。

具体算法网上都有介绍我就不再赘述，下面直接谈怎么编码实现吧:-)

对于Base64算法的C语言实现，大家可以参考Bob Trower的经典开源项目b64.c，网址是http://base64.sourceforge.net/。

在这里我要谈的是如何用ASP进行Base64编码，网上搜索出的一大堆算法不是太复杂就是运行不准确，其实ASP的Base64编码可以很简单，当然要用到服务器的一个COM组件XmlDom，具体思路是这样的，首先创建个临时的节点tmp，然后给结点tmp，设置datatype = “bin.base64″，这样就可以进行相应的编解码了，对于文本字符串的编解码还要用ADODB.Stream进行一次编码转换。

Base64的ASP实现：

Class CBase64
  Private objXmlDom
  Private objXmlNode

  ' GetObjectParam() 这个函数实现参考了开源项目PJBlog
  Private Function GetObjectParam()
   On Error Resume Next
   Dim Temp
   GetObjectParam = "Microsoft.XMLDOM"
   Err =
   Dim TmpObj
   Set TmpObj = Server.CreateObject(GetObjectParam)
   Temp = Err.Number
   If Temp =  Or Temp = - Then
       GetObjectParam = "Msxml2.DOMDocument.5.0"
    End If
    Err.Clear
    Set TmpObj = Nothing
   Err =
  End Function

  Private Sub Class_Initialize()
      Set objXmlDom = Server.CreateObject(GetObjectParam())
  End Sub

  Private Sub Class_Terminate()
      Set objXmlDom = Nothing
  End Sub

  Public Function encode(AnsiCode)
    encode = ""
    Set objXmlNode = objXmlDom.createElement("tmp")
    objXmlNode.datatype = "bin.base64"
    objXmlNode.nodeTypedvalue = AnsiCode
    encode = objXmlNode.Text
    Set objXmlNode = Nothing
  End Function

  Public Function decode(base64Code)
    On Error Resume Next
    decode = ""
    Set objXmlNode = objXmlDom.createElement("tmp")
    objXmlNode.datatype = "bin.base64"
    objXmlNode.Text = base64Code
    decode = objXmlNode.nodeTypedvalue
    Set objXmlNode = Nothing
    If Err Then
        Err.Clear
    End If
  End Function

  ' 以下函数编码字符串
  Public Function encodeText(ByVal str)
    On Error Resume Next
    Dim ado, r: r = ""
    If str <> "" Then
    Set ado = Server.CreateObject("ADODB.Stream")
        With ado
            .Charset = "gb2312"
            .Type =
            If .State =  Then .Open
            .WriteText str
            .Position =
            .Type =
            r = encode(.Read(-))
            .Close
        End With
    Set ado = Nothing
    End If
    If Err Then Err.Clear: r = ""
    encodeText = r
  End Function

  ' 以下函数解码字符串
  Public Function decodeText(ByVal str)
    On Error Resume Next
    Dim ado, r: r = ""
    If str <> "" Then
    Set ado = Server.CreateObject("ADODB.Stream")
        With ado
            .Charset = "gb2312"
            .Type =
            If .State =  Then .Open
            .Write (decode(str))
            .Position =
            .Type =
            r = .ReadText(-)
            .Close
        End With
    Set ado = Nothing
    End If
    If Err Then Err.Clear: r = ""
    decodeText = r
  End Function
End Class

写到这里想起以前项目里改写过一段Base64和16进制互转的代码，在这里与大家分享下。

' Base64转16进制
Function B64ToHex(ByVal strContent)
  Dim i,strReturned, b64pad, _
       b64map, chTemp, intLocate, k , slop
  strReturned = "" : k =
  b64map="ABCDEFGHIJKLMNOPQRSTUVWXYZ" &_
              "abcdefghijklmnopqrstuvwxyz0123456789+/"
  b64pad="="
  For i= To Len(strContent)-
     chTemp = Mid(strContent, i+, )
     If chTemp = b64pad Then Exit For
     intLocate = InStr(, b64map, chTemp, )-
     If intLocate > - Then
         Select Case K
           Case
           strReturned = strReturned &_
                             Int2Char(Int(intLocate / ))
           slop = intLocate And  :  k =
           Case
           strReturned = strReturned &_
                              Int2Char( (slop * ) Or (Int(intLocate / )) )
          slop = intLocate And &h0f :  k =
          Case
          strReturned = strReturned &_
                             Int2Char(slop) & Int2Char(Int(intLocate / ))
          slop = intLocate And   : k=
          Case Else
          strReturned = strReturned &_
                             Int2Char( (slop * ) Or (Int(intLocate / )) ) &_
                             Int2Char(intLocate And &h0f)
          k =
        End Select
     End If
  Next
  If k= Then strReturned = strReturned & Int2Char(slop * )
  B64ToHex = strReturned
End Function

' 16进制转Base64
Function HexToB64(ByVal strContent)
  Dim i, c, strReturned, b64map, b64pad, intLen
  b64map="ABCDEFGHIJKLMNOPQRSTUVWXYZ" &_
             "abcdefghijklmnopqrstuvwxyz0123456789+/"
  b64pad="="
  intLen = Len(strContent)
  For i= To intLen- Step
      c=Clng("&h" & Mid(strContent,i+,))
      strReturned = strReturned &_
                         Mid(b64map, Int(c /  +), ) &_
                         Mid(b64map, (c And )+, )
  Next

  If i+=intLen Then
     c =Clng("&h" & Mid(strContent,i+,))
     strReturned = strReturned & Mid(b64map, c *  + , )
  ElseIf i+=intLen Then
     c =Clng("&h" & Mid(strContent,i+,))
     strReturned = strReturned & Mid(b64map, Int(c / ) + , ) &_
                        Mid(b64map, (c And )*+, )
  End If

  While (Len(strReturned) And ) >
      strReturned = strReturned & b64pad
  Wend
  HexToB64 = strReturned
End Function

有关Base24的代码实现网上也有很多，这里给出两种不同程序语言的实现供参考。

Base24的C语言实现

static const char sel[] = {
    'B','C','D','F','G',
    'H','J','K','M','P',
    'Q','R','T','V','W',
    'X','Y','','','',
    '','','','', '\0'};

char *b24e(char *buf, unsigned char *byst, size_t sizeOfBytes)
{
    int i = ;
    unsigned char *p = byst;
    while ((size_t)(i = (p-byst)) < sizeOfBytes) {
        buf[*i] = sel[((*p) >> )];
        buf[(*i)+] = sel[ - ((*p) & 0x0f)];
        p++;
    }
    buf[(*i)+] = '\0';
    return buf;
}

unsigned char *b24d(unsigned char *buf, char *str, size_t countOfChars)
{
    size_t i;
    char *p = str;
    char *loc[];
    unsigned char n[];
    if (countOfChars % )
        return NULL;
    for (i = ; i < (countOfChars>>); i++) {

        loc[] = strchr( sel, str[*i] );
        loc[] = strchr( sel, str[ ( *i ) +  ] );
        if (loc[] == NULL || loc[] == NULL)
            return NULL;
        n[] = (unsigned char)( loc[] - sel );
        n[] =  - (unsigned char)( loc[] - sel );
        buf[i] = (unsigned char)((n[] << ) | n[]);
    }
    return buf;
}

后来由于项目需要，我特地改写了C#版。

public static class Base24
{
  private static string sel = "BCDFGHJKMPQRTVWXY2346789";

  public static string Encode(string Text)
  {
    int i = ;
    int Pos = ;
    char []Buf = new char[Text.Length<<];

    while ((i = Pos) < Text.Length)
    {
        Buf[i<<] = sel[(Text[Pos]) >> ];
        Buf[(i<<) + ] = sel[ - (Text[Pos] & 0x0F)];
        Pos++;
     }

        return new string(Buf);
    }

    public static string Decode(string Text)
    {
        if (Text.Length %  != )
            return null;

        int [] NPos = new int[];
        char[] N = new char[];
        char[] Buf = new char[Text.Length >> ];

        for (int i = ; i < (Text.Length >> ); i++)
        {
            NPos[] = sel.IndexOf(Text[ i<< ]);
            NPos[] =  - sel.IndexOf(Text[(i<<) + ]);
            if (NPos[] <  || NPos[] < ) {
                return null;
            }

            Buf[i] = ((char)((NPos[] << ) | NPos[]));
        }
            return new string(Buf);
    }
}

=============== End