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