base64

base64
在URL中的应用
VB版的Base64编码函数定义
JS版的Base64编码函数定义
C#实现BASE64加密、解密算法
Base64-MIME
在URL中的应用
VB版的Base64编码函数定义
JS版的Base64编码函数定义
C#实现BASE64加密、解密算法
Base64-MIME
Base64是网络上最常见的用于传输8Bit字节代码的编码方式之一，大家可以查看RFC2045～RFC2049，上面有MIME的详细规范。

Base64编码可用于在HTTP环境下传递较长的标识信息。

例如，在Java Persi stence系统Hibernate中，就采用了Base64来将一个较长的唯一标识符（一般为1 28-bit的UUID）编码为一个字符串，用作HTTP表单和HTTP GET URL中的参数。

在其他应用程序中，也常常需要把二进制数据编码为适合放在URL（包括隐藏表单域）中的形式。

此时，采用Base64编码不仅比较简短，同时也具有不可读性，即所编码的数据不会被人用肉眼所直接看到。

然而，标准的Base64并不适合直接放在URL里传输，因为URL编码器会把标准Base64中的“/”和“+”字符变为形如“%XX”的形式，而这些“%”号在存入数据库时还需要再进行转换，因为ANSI SQL中已将“%”号用作通配符。

为解决此问题，可采用一种用于URL的改进Base64编码，它不在末尾填充'='号，并将标准Base64中的“+”和“/”分别改成了“*”和“-”，这样就免去了在URL编解码和数据库存储时所要作的转换，避免了编码信息长度在此过程中的增加，并统一了数据库、表单等处对象标识符的格式。

另有一种用于正则表达式的改进Base64变种，它将“+”和“/”改成了“!”和“-”，因为“+”,“*”以及前面在IRCu中用到的“[”和“]”在正则表达式中都可能具有特殊含义。

此外还有一些变种，它们将“+/”改为“_-”或“._”（用作编程语言中的标识符名称）或“.-”（用于XML中的Nmtoken）甚至“_:”（用于XML中的Name）。

Base64要求把每三个8Bit的字节转换为四个6Bit的字节（3*8 = 4*6 = 24），然后把6Bit再添两位高位0，组成四个8Bit的字节，也就是说，转换后的字符串理论上将要比原来的长1/3。

关于这个编码的规则：
①.把3个字符变成4个字符..
②每76个字符加一个换行符..
③.最后的结束符也要处理..
这样说会不会太抽象了？不怕，我们来看一个例子：
转换前aaaaaabb ccccdddd eeffffff
转换后00aaaaaa 00bbcccc 00ddddee 00ffffff
应该很清楚了吧？上面的三个字节是原文，下面的四个字节是转换后的Base64编码，其前两位均为0。

转换后，我们用一个码表来得到我们想要的字符串（也就是最终的Base64编码），这个表是这样的：（摘自RFC2045）
Table 1: The Base64 Alphabet
Value Encoding Value Encoding Value Encoding Value Encoding
0 A 17 R 34 i 51 z
1 B 18 S 35 j 5
2 0
2 C 19 T 36 k 5
3 1
3 D 20 U 37 l 5
4 2
4 E 21 V 38 m 5
5 3
5 F 22 W 39 n 5
6 4
6 G 23 X 40 o 5
7 5
7 H 24 Y 41 p 58 6
8 I 25 Z 42 q 59 7
9 J 26 a 43 r 60 8
10 K 27 b 44 s 61 9
11 L 28 c 45 t 62 +
12 M 29 d 46 u 63 /
13 N 30 e 47 v
14 O 31 f 48 w (pad) =
15 P 32 g 49 x
16 Q 33 h 50 y
让我们再来看一个实际的例子，加深印象！
转换前10101101 10111010 01110110
转换后00101011 00011011 00101001 00110110
十进制43 27 41 54
对应码表中的值r b p 2
所以上面的24位编码，编码后的Base64值为rbp2
解码同理，把rbq2 的二进制位连接上再重组得到三个8位值，得出原码。

（解码只是编码的逆过程，在此我就不多说了，另外有关MIME的RFC还是有很多的，如果需要详细情况请自行查找。

）
用更接近于编程的思维来说，编码的过程是这样的：
第一个字符通过右移2位获得第一个目标字符的Base64表位置，根据这个数值取到表上相应的字符，就是第一个目标字符。

然后将第一个字符左移4位加上第二个字符右移4位，即获得第二个目标字符。

再将第二个字符左移2位加上第三个字符右移6位，获得第三个目标字符。

最后取第三个字符的右6位即获得第四个目标字符。

在以上的每一个步骤之后，再把结果与0x3F 进行AND 位操作，就可以得到编码后的字符了。

可是等等……聪明的你可能会问到，原文的字节数量应该是3的倍数啊，如果这个条件不能满足的话，那该怎么办呢？
我们的解决办法是这样的：原文的字节不够的地方可以用全0来补足，转换时B ase64编码用=号来代替。

这就是为什么有些Base64编码会以一个或两个等号结束的原因，但等号最多只有两个。

因为：
余数= 原文字节数MOD 3
所以余数任何情况下都只可能是0，1，2这三个数中的一个。

如果余数是0的话，就表示原文字节数正好是3的倍数（最理想的情况啦）。

如果是1的话，为了让Ba se64编码是3的倍数，就要补2个等号；同理，如果是2的话，就要补1个等号。

[编辑本段]
在URL中的应用
Base64编码可用于在HTTP环境下传递较长的标识信息。

例如，在Java Persi stence系统Hibernate中，就采用了Base64来将一个较长的唯一标识符（一般为1 28-bit的UUID）编码为一个字符串，用作HTTP表单和HTTP GET URL中的参数。

在其他应用程序中，也常常需要把二进制数据编码为适合放在URL（包括隐藏表单域）中的形式。

此时，采用Base64编码不仅比较简短，同时也具有不可读性，即所编码的数据不会被人用肉眼所直接看到。

然而，标准的Base64并不适合直接放在URL里传输，因为URL编码器会把标准Base64中的“/”和“+”字符变为形如“%XX”的形式，而这些“%”号在存入数据库时还需要再进行转换，因为ANSI SQL中已将“%”号用作通配符。

为解决此问题，可采用一种用于URL的改进Base64编码，它不在末尾填充'='号，并将标准Base64中的“+”和“/”分别改成了“*”和“-”，这样就免去了在URL编解码和数据库存储时所要作的转换，避免了编码信息长度在此过程中的增加，并统一了数据库、表单等处对象标识符的格式。

另有一种用于正则表达式的改进Base64变种，它将“+”和“/”改成了“!”和“-”，因为“+”,“*”以及前面在IRCu中用到的“[”和“]”在正则表达式中都可能具有特殊含义。

此外还有一些变种，它们将“+/”改为“_-”或“._”（用作编程语言中的标识符名称）或“.-”（用于XML中的Nmtoken）甚至“_:”（用于XML中的Name）。

在下载软件中加密下载地址的原理
先以“迅雷下载”为例：很多下载类网站都提供“迅雷下载”的链接，其地址通常是加密的迅雷专用下载地址。

如thunder://QUFodHRwOi8vd3d3LmJhaWR1LmNvbS9pbWcvc3NsbTFfbG9nb y5naWZaWg==
其实迅雷的“专用地址”也是用Base64加密的，其加密过程如下：
一、在地址的前后分别添加AA和ZZ
如/img/sslm1_logo.gif变成
/img/sslm1_logo.gifZZ
二、对新的字符串进行Base64编码
如/img/sslm1_logo.gifZZ用Base64编码得到
QUFodHRwOi8vd3d3LmJhaWR1LmNvbS9pbWcvc3NsbTFfbG9nby5naWZaW g==
三、在上面得到的字符串前加上“thunder://”就成了
thunder://QUFodHRwOi8vd3d3LmJhaWR1LmNvbS9pbWcvc3NsbTFfbG9nby5 naWZaWg==
另：
Flashget的与迅雷类似，只不过在第一步时加的“料”不同罢了，Flashget在地址前后加的“料”是[FLASHGET]
而QQ旋风的干脆不加料，直接就对地址进行Base64编码了
PHP中的解密下载地址的实现
[下列代码仅在GBK中实现，UTF8代码请把if($button=="迅雷地址->普通地址") echo substr(base64_decode(str_ireplace("thunder://","",$txt1)),2,-2); 这句改为if($button=="迅雷地址->普通地址") echo substr(mb_convert_encoding(base64_d ecode(str_ireplace("thunder://","",$txt1))),2,-2); 并把charset=gb2312改为charset =utf-8]
<?php
$txt1=trim($_POST['text1']);
$txt2=trim($_POST['text2']);
$txt3=trim($_POST['text3']);
$button=$_POST['button'];
?>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" > <html>
<head>
<title>迅雷和FlashGet,QQ旋风地址地址转换工具</title>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312">
<meta content="迅雷,FlashGet,地址转换," name="keywords">
</head>
<body>
<form name="form1" method="post" action="">
<hr size="1">
<h3>迅雷转换</h3>
<P>转换地址：
<input name="text1" value="<?php echo $txt1;?>" type="text" style="width: 516px;" /></P>
<P>转换后的：
<input type="text" value="<?php
if($button=="普通地址->迅雷地址") echo "thunder://".base64_encode("AA".$t xt1."ZZ");
if($button=="迅雷地址->普通地址") echo substr(base64_decode(str_ireplace ("thunder://","",$txt1)),2,-2);
?>" style="width:516px;" /></P>
<P>
<input type="submit" name="button" value="普通地址->迅雷地址" />
<input type="submit" name="button" value="迅雷地址->普通地址" /></P> <h3>FlashGet转换</h3>
<P>FlashGet地址：
<input name="text2" value="<?php echo $txt2;?>" type="text" style="width: 516px;" /></P>
<P>转换后地址：
<input type="text" value="<?php
if($button=="普通地址->FlashGet地址") echo "flashget://".base64_encode($t xt2);
if($button=="FlashGet地址->普通地址") echo str_ireplace("[FLASHGET]","",b ase64_decode(str_ireplace("flashget://","",$txt2)));
?>" style="width:516px;" /></P>
<P>
<input type="submit" value="普通地址->FlashGet地址" name="button" /> <input type="submit" value="FlashGet地址->普通地址" name="button" /></ P>
<h3>QQ旋风转换</h3>
<P>QQ旋风地址：
<input name="text3" value="<?php echo $txt3;?>" type="text" style="width: 516px;" /></P>
<P>转换后地址：
<input type="text" value="<?php
if($button=="普通地址->QQ旋风") echo "qqdl://".base64_encode($txt3);
if($button=="QQ旋风->普通地址") echo base64_decode(str_ireplace("qqdl://", "",$txt3));
?>" style="width:516px;" /></P>
<P>
<input type="submit" value="普通地址->QQ旋风" name="button" />
<input type="submit" value="QQ旋风->普通地址" name="button" /></P> </form>
</body>
</html>
[编辑本段]
VB版的Base64编码函数定义
注:其中DigestStrToHexStr为可在程序外部调用加密函数
Option Explicit
' Base64 Encoding/Decoding Algorithm
' By: David Midkiff (mznull@)
'
' This algorithms encodes and decodes data into Base64
' format. This format is extremely more efficient than
' Hexadecimal encoding.
Private m_bytIndex(0 To 63) As Byte
Private m_bytReverseIndex(0 To 255) As Byte
Private Const k_bytEqualSign As Byte = 61
Private Const k_bytMask1 As Byte = 3
Private Const k_bytMask2 As Byte = 15
Private Const k_bytMask3 As Byte = 63
Private Const k_bytMask4 As Byte = 192
Private Const k_bytMask5 As Byte = 240
Private Const k_bytMask6 As Byte = 252
Private Const k_bytShift2 As Byte = 4
Private Const k_bytShift4 As Byte = 16
Private Const k_bytShift6 As Byte = 64
Private Const k_lMaxBytesPerLine As Long = 152
Private Declare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" (ByVal Destination As Long, ByVal Source As Long, ByVal Length As Long) Public Function Decode64(sInput As String) As String
If sInput = "" Then Exit Function
Decode64 = StrConv(DecodeArray64(sInput), vbUnicode)
End Function
Private Function DecodeArray64(sInput As String) As Byte()
Dim bytInput() As Byte
Dim bytWorkspace() As Byte
Dim bytResult() As Byte
Dim lInputCounter As Long
Dim lWorkspaceCounter As Long
bytInput = Replace(Replace(sInput, vbCrLf, ""), "=", "")
ReDim bytWorkspace(LBound(bytInput) To (UBound(bytInput) * 2))As Byt e
lWorkspaceCounter = LBound(bytWorkspace)
For lInputCounter = LBound(bytInput) To UBound(bytInput)
bytInput(lInputCounter) = m_bytReverseIndex(bytInput(lInputCounter))
Next lInputCounter
For lInputCounter = LBound(bytInput) To (UBound(byt Input) - ((UBound(b ytInput) Mod 8) + 8)) Step 8
bytWorkspace(lWorkspaceCounter) = (bytInput(lInputCounter) * k_bytShift2) + (bytInput(lInputCounter + 2) \ k_bytShift4)
bytWorkspace(lWorkspaceCounter + 1) = ((bytInput(lInputCounter + 2) An d k_bytMask2) * k_bytShift4) + (bytInput(lInputCounter + 4) \ k_bytShift2)
bytWorkspace(lWorkspaceCounter + 2) = ((bytInput(lInputCounter + 4) An d k_bytMask1) * k_bytShift6) + bytInput(lInputCounter + 6)
lWorkspaceCounter = lWorkspaceCounter + 3
Next lInputCounter
Select Case (UBound(bytInput) Mod 8):
Case 3:
bytWorkspace(lWorkspaceCounter) = (bytInput(lInputCounter) * k_bytShift2) + (bytInput(lInputCounter + 2) \ k_bytShift4)
Case 5:
bytWorkspace(lWorkspaceCounter) = (bytInput(lInputCounter) * k_bytShift2) + (bytInput(lInputCounter + 2) \ k_bytShift4)
bytWorkspace(lWorkspaceCounter + 1) = ((bytInput(lInputCounter + 2) An d k_bytMask2) * k_bytShift4) + (bytInput(lInputCounter + 4) \ k_bytShift2)
lWorkspaceCounter = lWorkspaceCounter + 1
Case 7:
bytWorkspace(lWorkspaceCounter) = (bytInput(lInputCounter) * k_bytShift2) + (bytInput(lInputCounter + 2) \ k_bytShift4)
bytWorkspace(lWorkspaceCounter + 1) = ((bytInput(lInputCounter + 2) An d k_bytMask2) * k_bytShift4) + (bytInput(lInputCounter + 4) \ k_bytShift2)
bytWorkspace(lWorkspaceCounter + 2) = ((bytInput(lInputCounter + 4) An d k_bytMask1) * k_bytShift6) + bytInput(lInputCounter + 6)
lWorkspaceCounter = lWorkspaceCounter + 2
End Select
ReDim bytResult(LBound(bytWorkspace) To lWorkspaceCounter) As Byte If LBound(bytWorkspace) = 0 Then lWorkspaceCounter = lWorkspaceCou nter + 1
CopyMemory VarPtr(bytResult(LBound(bytResult))), VarPtr(bytWorkspace(L Bound(bytWorkspace))), lWorkspaceCounter
DecodeArray64 = bytResult
End Function
Public Function Encode64(ByRef sInput As String) As String
If sInput = "" Then Exit Function
Dim bytTemp() As Byte
bytTemp = StrConv(sInput, vbFromUnicode)
Encode64 = EncodeArray64(bytTemp)
End Function
Private Function EncodeArray64(ByRef bytInput() As Byte) As String
On Error GoTo ErrorHandler
Dim bytWorkspace() As Byte, bytResult() As Byte
Dim bytCrLf(0 To 3) As Byte, lCounter As Long
Dim lWorkspaceCounter As Long, lLineCounter As Long
Dim lCompleteLines As Long, lBytesRemaining As Long
Dim lpWorkSpace As Long, lpResult As Long
Dim lpCrLf As Long
If UBound(bytInput) < 1024 Then
ReDim bytWorkspace(LBound(bytInput) To (LBound(bytInput) + 4096)) As Byte
Else
ReDim bytWorkspace(LBound(bytInput) To (UBound(bytInput) * 4)) As Byt e
End If
lWorkspaceCounter = LBound(bytWorkspace)
For lCounter = LBound(bytInput) To (UBound(bytInput) - ((UBound(bytInp ut) Mod 3) + 3)) Step 3
bytWorkspace(lWorkspaceCounter) = m_bytIndex((bytInput(lCounter) \ k_b ytShift2))
bytWorkspace(lWorkspaceCounter + 2) = m_bytIndex(((bytInput(lCounter) And k_bytMask1) * k_bytShift4) + ((bytInput(lCounter + 1)) \ k_bytShift4)) bytWorkspace(lWorkspaceCounter + 4) = m_bytIndex(((bytInput(lCounter + 1) And k_bytMask2) * k_bytShift2) + (bytInput(lCounter + 2) \ k_bytShift6))
bytWorkspace(lWorkspaceCounter + 6) = m_bytIndex(bytInput(lCounter + 2) And k_bytMask3)
lWorkspaceCounter = lWorkspaceCounter + 8
Next lCounter
Select Case (UBound(bytInput) Mod 3):
Case 0:
bytWorkspace(lWorkspaceCounter) = m_bytIndex((bytInput(lCounter) \ k_b ytShift2))
bytWorkspace(lWorkspaceCounter + 2) = m_bytIndex((bytInput(lCounter) A nd k_bytMask1) * k_bytShift4)
bytWorkspace(lWorkspaceCounter + 4) = k_bytEqualSign
bytWorkspace(lWorkspaceCounter + 6) = k_bytEqualSign
Case 1:
bytWorkspace(lWorkspaceCounter) = m_bytIndex((bytInput(lCounter) \ k_b ytShift2))
bytWorkspace(lWorkspaceCounter + 2) = m_bytIndex(((bytInput(lCounter) And k_bytMask1) * k_bytShift4) + ((bytInput(lCounter + 1)) \ k_bytShift4)) bytWorkspace(lWorkspaceCounter + 4) = m_bytIndex((bytInput(lCounter + 1) And k_bytMask2) * k_bytShift2)
bytWorkspace(lWorkspaceCounter + 6) = k_bytEqualSign
Case 2:
bytWorkspace(lWorkspaceCounter) = m_bytIndex((bytInput(lCounter) \ k_b ytShift2))
bytWorkspace(lWorkspaceCounter + 2) = m_bytIndex(((bytInput(lCounter) And k_bytMask1) * k_bytShift4) + ((bytInput(lCounter + 1)) \ k_bytShift4)) bytWorkspace(lWorkspaceCounter + 4) = m_bytIndex(((bytInput(lCounter + 1) And k_bytMask2) * k_bytShift2) + ((bytInput(lCounter + 2)) \ k_bytShift6))
bytWorkspace(lWorkspaceCounter + 6) = m_bytIndex(bytInput(lCounter + 2) And k_bytMask3)
End Select
lWorkspaceCounter = lWorkspaceCounter + 8
If lWorkspaceCounter <= k_lMaxBytesPerLine Then
EncodeArray64 = Left$(bytWorkspace, InStr(1, bytWorkspace, Chr$(0)) - 1)
Else
bytCrLf(0) = 13
bytCrLf(1) = 0
bytCrLf(2) = 10
bytCrLf(3) = 0
ReDim bytResult(LBound(bytWorkspace) To UBound(bytWorkspace))
lpWorkSpace = VarPtr(bytWorkspace(LBound(bytWorkspace)))
lpResult = VarPtr(bytResult(LBound(bytResult)))
lpCrLf = VarPtr(bytCrLf(LBound(bytCrLf)))
lCompleteLines = Fix(lWorkspaceCounter / k_lMaxBytesPerLine)
For lLineCounter = 0 To lCompleteLines
CopyMemory lpResult, lpWorkSpace, k_lMaxBytesPerLine
lpWorkSpace = lpWorkSpace + k_lMaxBytesPerLine
lpResult = lpResult + k_lMaxBytesPerLine
CopyMemory lpResult, lpCrLf, 4&
lpResult = lpResult + 4&
Next lLineCounter
lBytesRemaining = lWorkspaceCounter - (lCompleteLines * k_lMaxBytesP erLine)
If lBytesRemaining > 0 Then CopyMemory lpResult, lpWorkSpace, lBytes Remaining
EncodeArray64 = Left$(bytResult, InStr(1, bytResult, Chr$(0)) - 1)
End If
Exit Function
ErrorHandler:
Erase bytResult
EncodeArray64 = bytResult
End Function
Private Sub Class_Initia lize()
m_bytIndex(0) = 65 'Asc("A")
m_bytIndex(1) = 66 'Asc("B")
m_bytIndex(2) = 67 'Asc("C")
m_bytIndex(3) = 68 'Asc("D")
m_bytIndex(4) = 69 'Asc("E")
m_bytIndex(5) = 70 'Asc("F")
m_bytIndex(6) = 71 'Asc("G")
m_bytIndex(7) = 72 'Asc("H")
m_bytIndex(8) = 73 'Asc("I")
m_bytIndex(9) = 74 'Asc("J")
m_bytIndex(10) = 75 'Asc("K")
m_bytIndex(11) = 76 'Asc("L")
m_bytIndex(12) = 77 'Asc("M")
m_bytIndex(14) = 79 'Asc("O") m_bytIndex(15) = 80 'Asc("P") m_bytIndex(16) = 81 'Asc("Q") m_bytIndex(17) = 82 'Asc("R") m_bytIndex(18) = 83 'Asc("S") m_bytIndex(19) = 84 'Asc("T") m_bytIndex(20) = 85 'Asc("U") m_bytIndex(21) = 86 'Asc("V") m_bytIndex(22) = 87 'Asc("W") m_bytIndex(23) = 88 'Asc("X") m_bytIndex(24) = 89 'Asc("Y") m_bytIndex(25) = 90 'Asc("Z") m_bytIndex(26) = 97 'Asc("a") m_bytIndex(27) = 98 'Asc("b") m_bytIndex(28) = 99 'Asc("c") m_bytIndex(29) = 100 'Asc("d") m_bytIndex(30) = 101 'Asc("e") m_bytIndex(31) = 102 'Asc("f") m_bytIndex(32) = 103 'Asc("g") m_bytIndex(33) = 104 'Asc("h") m_bytIndex(34) = 105 'Asc("i") m_bytIndex(35) = 106 'Asc("j") m_bytIndex(36) = 107 'Asc("k") m_bytIndex(37) = 108 'Asc("l") m_bytIndex(38) = 109 'Asc("m") m_bytIndex(39) = 110 'Asc("n") m_bytIndex(40) = 111 'Asc("o") m_bytIndex(41) = 112 'Asc("p") m_bytIndex(42) = 113 'Asc("q") m_bytIndex(43) = 114 'Asc("r") m_bytIndex(44) = 115 'Asc("s") m_bytIndex(45) = 116 'Asc("t") m_bytIndex(46) = 117 'Asc("u") m_bytIndex(47) = 118 'Asc("v") m_bytIndex(48) = 119 'Asc("w") m_bytIndex(49) = 120 'Asc("x") m_bytIndex(50) = 121 'Asc("y")
m_bytIndex(52) = 48 'Asc("0")
m_bytIndex(53) = 49 'Asc("1")
m_bytIndex(54) = 50 'Asc("2")
m_bytIndex(55) = 51 'Asc("3")
m_bytIndex(56) = 52 'Asc("4")
m_bytIndex(57) = 53 'Asc("5")
m_bytIndex(58) = 54 'Asc("6")
m_bytIndex(59) = 55 'Asc("7")
m_bytIndex(60) = 56 'Asc("8")
m_bytIndex(61) = 57 'Asc("9")
m_bytIndex(62) = 43 'Asc("+")
m_bytIndex(63) = 47 'Asc("/")
m_bytReverseIndex(65) = 0 'Asc("A") m_bytReverseIndex(66) = 1 'Asc("B") m_bytReverseIndex(67) = 2 'Asc("C") m_bytReverseIndex(68) = 3 'Asc("D") m_bytReverseIndex(69) = 4 'Asc("E") m_bytReverseIndex(70) = 5 'Asc("F") m_bytReverseIndex(71) = 6 'Asc("G") m_bytReverseIndex(72) = 7 'Asc("H") m_bytReverseIndex(73) = 8 'Asc("I")
m_bytReverseIndex(74) = 9 'Asc("J")
m_bytReverseIndex(75) = 10 'Asc("K") m_bytReverseIndex(76) = 11 'Asc("L") m_bytReverseIndex(77) = 12 'Asc("M") m_bytReverseIndex(78) = 13 'Asc("N") m_bytReverseIndex(79) = 14 'Asc("O") m_bytReverseIndex(80) = 15 'Asc("P") m_bytReverseIndex(81) = 16 'Asc("Q") m_bytReverseIndex(82) = 17 'Asc("R") m_bytReverseIndex(83) = 18 'Asc("S") m_bytReverseIndex(84) = 19 'Asc("T") m_bytReverseIndex(85) = 20 'Asc("U") m_bytReverseIndex(86) = 21 'Asc("V") m_bytReverseIndex(87) = 22 'Asc("W") m_bytReverseIndex(88) = 23 'Asc("X") m_bytReverseIndex(89) = 24 'Asc("Y")
m_bytReverseIndex(97) = 26 'Asc("a") m_bytReverseIndex(98) = 27 'Asc("b") m_bytReverseIndex(99) = 28 'Asc("c") m_bytReverseIndex(100) = 29 'Asc("d") m_bytReverseIndex(101) = 30 'Asc("e") m_bytReverseIndex(102) = 31 'Asc("f") m_bytReverseIndex(103) = 32 'Asc("g") m_bytReverseIndex(104) = 33 'Asc("h") m_bytReverseIndex(105) = 34 'Asc("i") m_bytReverseIndex(106) = 35 'Asc("j") m_bytReverseIndex(107) = 36 'Asc("k") m_bytReverseIndex(108) = 37 'Asc("l") m_bytReverseIndex(109) = 38 'Asc("m") m_bytReverseIndex(110) = 39 'Asc("n") m_bytReverseIndex(111) = 40 'Asc("o") m_bytReverseIndex(112) = 41 'Asc("p") m_bytReverseIndex(113) = 42 'Asc("q") m_bytReverseIndex(114) = 43 'Asc("r") m_bytReverseIndex(115) = 44 'Asc("s") m_bytReverseIndex(116) = 45 'Asc("t") m_bytReverseIndex(117) = 46 'Asc("u") m_bytReverseIndex(118) = 47 'Asc("v") m_bytReverseIndex(119) = 48 'Asc("w") m_bytReverseIndex(120) = 49 'Asc("x") m_bytReverseIndex(121) = 50 'Asc("y") m_bytReverseIndex(122) = 51 'Asc("z") m_bytReverseIndex(48) = 52 'Asc("0") m_bytReverseIndex(49) = 53 'Asc("1") m_bytReverseIndex(50) = 54 'Asc("2") m_bytReverseIndex(51) = 55 'Asc("3") m_bytReverseIndex(52) = 56 'Asc("4") m_bytReverseIndex(53) = 57 'Asc("5") m_bytReverseIndex(54) = 58 'Asc("6") m_bytReverseIndex(55) = 59 'Asc("7") m_bytReverseIndex(56) = 60 'Asc("8") m_bytReverseIndex(57) = 61 'Asc("9") m_bytReverseIndex(43) = 62 'Asc("+")
End Sub
[编辑本段]
JS版的Base64编码函数定义
var base64EncodeChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefgh ijklmnopqrstuvwxyz0123456789+/";
var base64DecodeChars = new Array(
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63,
52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1, -1, -1,
-1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,
15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1,
-1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1);
function base64encode(str)
{
var returnVal, i, len;
var c1, c2, c3;
len = str.length;
i = 0;
returnVal = "";
while(i < len)
{
c1 = str.charCodeAt(i++) & 0xff;
if(i == len)
{
returnVal += base64EncodeChars.charAt(c1 >> 2);
returnVal += base64EncodeChars.charAt((c1 & 0x3) << 4);
returnVal += "==";
break;
}
c2 = str.charCodeAt(i++);
if(i == len)
{
returnVal += base64EncodeChars.charAt(c1 >> 2);
returnVal += base64EncodeChars.charAt(((c1 & 0x3)<< 4) | ((c2 & 0xF0) >> 4));
returnVal += base64EncodeChars.charAt((c2 & 0xF) << 2);
returnVal += "=";
break;
}
c3 = str.charCodeAt(i++);
returnVal += base64EncodeChars.charAt(c1 >> 2);
returnVal += base64EncodeChars.charAt(((c1 & 0x3)<< 4) | ((c2 & 0xF0) >> 4));
returnVal += base64EncodeChars.charAt(((c2 & 0xF) << 2) | ((c3 & 0xC 0) >>6));
returnVal += base64EncodeChars.charAt(c3 & 0x3F);
}
return returnVal;
}
function base64decode(str)
{
var c1, c2, c3, c4;
var i, len, returnVal;
len = str.length;
i = 0;
returnVal = "";
while(i < len)
{
/* c1 */
do
{
c1 = base64DecodeChars[str.charCodeAt(i++) & 0xff];
} while(i < len && c1 == -1);
if(c1 == -1)
break;
/* c2 */
do
{
c2 = base64DecodeChars[str.charCodeAt(i++) & 0xff];
} while(i < len && c2 == -1);
if(c2 == -1)
break;
returnVal += String.fromCharCode((c1 << 2) | ((c2 & 0x30) >> 4));
/* c3 */
do
{
c3 = str.charCodeAt(i++) & 0xff;
if(c3 == 61)
return returnVal;
c3 = base64DecodeChars[c3];
} while(i < len && c3 == -1);
if(c3 == -1)
break;
returnVal += String.fromCharCode(((c2 & 0XF) << 4) | ((c3 & 0x3C) >> 2));
/* c4 */
do
{
c4 = str.charCodeAt(i++) & 0xff;
if(c4 == 61)
return returnVal;
c4 = base64DecodeChars[c4];
} while(i < len && c4 == -1);
if(c4 == -1)
break;
returnVal += String.fromCharCode(((c3 & 0x03) << 6) | c4);
}
return returnVal;
}
AS3版的Base64
package crypto{
import flash.utils.ByteArray;
public class Base64 {
private static const BASE64_CHARS:String = "ABCDEFGHIJKLMNOPQRS TUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";
public static function encode(data:String):String {
// Convert string to ByteArray
var bytes:ByteArray = new ByteArray();
bytes.writeUTFBytes(data);
// Return encoded ByteArray
return encodeByteArray(bytes);
}
public static function encodeByteArray(data:ByteArray):String {
// Initialise output
var output:String = "";
// Create data and output buffers
var dataBuffer:Array;
var outputBuffer:Array = new Array(4);
// Rewind ByteArray
data.position = 0;
// while there are still bytes to be processed
while (data.bytesAvailable > 0) {
// Create new data buffer and populate next 3 bytes from data dataBuffer = new Array();
for (var i:uint = 0; i < 3 && data.bytesAvailable > 0; i++) {
dataBuffer= data.readUnsignedByte();
}
// Convert to data buffer Base64 character positions and
// store in output buffer
outputBuffer[0] = (dataBuffer[0] & 0xfc) >> 2;
outputBuffer[1] = ((dataBuffer[0] & 0x03) << 4) | ((dataBuffer[1]) >> 4); outputBuffer[2] = ((dataBuffer[1] & 0x0f) << 2) | ((dataBuffer[2]) >> 6); outputBuffer[3] = dataBuffer[2] & 0x3f;
// If data buffer was short (i.e not 3 characters) then set
// end character indexes in data buffer to index of '=' symbol.
// This is necessary because Base64 data is always a multiple of
// 4 bytes and is basses with '=' symbols.
for (var j:uint = dataBuffer.length; j < 3; j++) {
outputBuffer[j + 1] = 64;
}
// Loop through output buffer and add Base64 characters to
// encoded data string for each character.
for (var k:uint = 0; k < outputBuffer.length; k++) {
output += BASE64_CHARS.charAt(outputBuffer[k]);
}
}
// Return encoded data
return output;
}
public static function decode(data:String):String {
// Decode data to ByteArray
var bytes:ByteArray = decodeToByteArray(data);
// Convert to string and return
return bytes.readUTFBytes(bytes.length);
}
public static function decodeToByteArray(data:String):ByteArray {
// Initialise output ByteArray for decoded data
var output:ByteArray = new ByteArray();
// Create data and output buffers
var dataBuffer:Array = new Array(4);
var outputBuffer:Array = new Array(3);
// While there are data bytes left to be processed
for (var i:uint = 0; i < data.length; i += 4) {
// Populate data buffer with position of Base64 characters for
// next 4 bytes from encoded data
for (var j:uint = 0; j < 4 && i + j < data.length; j++) {
dataBuffer[j] = BASE64_CHARS.indexOf(data.charAt(i + j));
}
// Decode data buffer back into bytes
outputBuffer[0] = (dataBuffer[0] << 2) + ((dataBuffer[1] & 0x30) >> 4);
outputBuffer[1] = ((dataBuffer[1] & 0x0f) << 4) + ((dataBuffer[2] & 0x3c) >> 2);
outputBuffer[2] = ((dataBuffer[2] & 0x03) << 6) + dataBuffer[3];
// Add all non-padded bytes in output buffer to decoded data
for (var k:uint = 0; k < outputBuffer.length; k++) {
if (dataBuffer[k+1] == 64) break;
output.writeByte(outputBuffer[k]);
}
}
// Rewind decoded data ByteArray
output.position = 0;
// Return decoded data
return output;
}
public function Base64() {
throw new Error("Base64 class is static container only");
}
}
}
JS实现BASE64加密、解密算法
此算法只适用于加密ASCII映射表中的字符组成的字符串，不能处理中文字符串等：
脚本如下：
<script language=javascript>
var base64EncodeChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefgh ijklmnopqrstuvwxyz0123456789+/";
var base64DecodeChars = new Array(
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63,
52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1, -1, -1,
-1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,
15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1,
-1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1);
function base64encode(str) {
var out, i, len;
var c1, c2, c3;
len = str.length;
i = 0;
out = "";
while(i < len) {
c1 = str.charCodeAt(i++) & 0xff;
if(i == len)
{
out += base64EncodeChars.charAt(c1 >> 2);
out += base64EncodeChars.charAt((c1 & 0x3) << 4);
out += "==";
break;
}
c2 = str.charCodeAt(i++);
if(i == len)
{。