“base64”的意思、由来-中文百科全书

标准的Base64

简介

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。

规则

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）

转换表

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 52 0

2 C 19 T 36 k 53 1

3 D 20 U 37 l 54 2

4 E 21 V 38 m 55 3

5 F 22 W 39 n 56 4

6 G 23 X 40 o 57 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

索引　对应字符　索引　对应字符　索引　对应字符　索引　对应字符

0　A　17　R　34　i　51　z

1　B　18　S　35　j　52　0

2　C　19　T　36　k　53　1

3　D　20　U　37　l　54　2

4　E　21　V　38　m　55　3

5　F　22　W　39　n　56　4

6　G　23　X　40　o　57　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　
　

15　P　32　g　49　x　
　

16　Q　33　h　50　y　
　

举例

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Base64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Base64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。

Base64编码可用于在HTTP环境下传递较长的标识信息。例如，在Java Persistence系统Hibernate中，就采用了Base64来将一个较长的唯一标识符（一般为128-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。

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://QUFodHRwOi8vd3d3LmJhaWR1LmNvbS9pbWcvc3NsbTFfbG9nby5naWZaWg==

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www.baidu.com/img/sslm1_logo.gif变成

AAwww.baidu.com/img/sslm1_logo.gifZZ

二、对新的字符串进行Base64编码

如AAwww.baidu.com/img/sslm1_logo.gifZZ用Base64编码得到

QUF3d3cuYmFpZHUuY29tL2ltZy9zc2xtMV9sb2dvLmdpZlpa

三、在上面得到的字符串前加上“thunder://”就成了

thunder://QUF3d3cuYmFpZHUuY29tL2ltZy9zc2xtMV9sb2dvLmdpZlpa

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($button=="迅雷地址->普通地址") echo substr(mb_convert_encoding(base64_decode(str_ireplace("thunder://","",$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>

</head>

<body>

<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($button=="普通地址->迅雷地址") echo "thunder://".base64_encode("AA".$txt1."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>

<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($button=="普通地址->FlashGet地址") echo "flashget://".base64_encode($txt2);

if($button=="FlashGet地址->普通地址") echo str_ireplace("[FLASHGET]","",base64_decode(str_ireplace("flashget://","",$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>

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@earthlink.net)

' 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 Byte

lWorkspaceCounter = LBound(bytWorkspace)

For lInputCounter = LBound(bytInput) To UBound(bytInput)

bytInput(lInputCounter) = m_bytReverseIndex(bytInput(lInputCounter))

Next lInputCounter

For lInputCounter = LBound(bytInput) To (UBound(bytInput) - ((UBound(bytInput) Mod 8) + 8)) Step 8

bytWorkspace(lWorkspaceCounter) = (bytInput(lInputCounter) * k_bytShift2) + (bytInput(lInputCounter + 2) \\ k_bytShift4)

bytWorkspace(lWorkspaceCounter + 1) = ((bytInput(lInputCounter + 2) And k_bytMask2) * k_bytShift4) + (bytInput(lInputCounter + 4) \\ k_bytShift2)

bytWorkspace(lWorkspaceCounter + 2) = ((bytInput(lInputCounter + 4) And 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) And 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) And k_bytMask2) * k_bytShift4) + (bytInput(lInputCounter + 4) \\ k_bytShift2)

bytWorkspace(lWorkspaceCounter + 2) = ((bytInput(lInputCounter + 4) And 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 = lWorkspaceCounter + 1

CopyMemory VarPtr(bytResult(LBound(bytResult))), VarPtr(bytWorkspace(LBound(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 Byte

End If

lWorkspaceCounter = LBound(bytWorkspace)

For lCounter = LBound(bytInput) To (UBound(bytInput) - ((UBound(bytInput) Mod 3) + 3)) Step 3

bytWorkspace(lWorkspaceCounter) = m_bytIndex((bytInput(lCounter) \\ k_bytShift2))

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_bytShift2))

bytWorkspace(lWorkspaceCounter + 2) = m_bytIndex((bytInput(lCounter) And k_bytMask1) * k_bytShift4)

bytWorkspace(lWorkspaceCounter + 4) = k_bytEqualSign

bytWorkspace(lWorkspaceCounter + 6) = k_bytEqualSign

Case 1:

bytWorkspace(lWorkspaceCounter) = m_bytIndex((bytInput(lCounter) \\ k_bytShift2))

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_bytShift2))

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_lMaxBytesPerLine)

If lBytesRemaining > 0 Then CopyMemory lpResult, lpWorkSpace, lBytesRemaining

EncodeArray64 = Left$(bytResult, InStr(1, bytResult, Chr$(0)) - 1)

End If

Exit Function

ErrorHandler:

Erase bytResult

EncodeArray64 = bytResult

End Function

Private Sub Class_Initialize()

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(13) = 78 'Asc("N")

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(51) = 122 'Asc("z")

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(90) = 25 'Asc("Z")

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("+")

m_bytReverseIndex(47) = 63 'Asc("/")

End Sub

JS版的Base64编码函数定义

var base64EncodeChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

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, 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 & 0xC0) >>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 */

{

c1 = base64DecodeChars[str.charCodeAt(i++) & 0xff];

} while(i < len && c1 == -1);

if(c1 == -1)

break;

/* c2 */

{

c2 = base64DecodeChars[str.charCodeAt(i++) & 0xff];

} while(i < len && c2 == -1);

if(c2 == -1)

break;

returnVal += String.fromCharCode((c1 << 2) | ((c2 & 0x30) >> 4));

/* c3 */

{

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 */

{

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 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";

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：

var base64EncodeChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

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, 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)

{

out += base64EncodeChars.charAt(c1 >> 2);

out += base64EncodeChars.charAt(((c1 & 0x3)<< 4) | ((c2 & 0xF0) >> 4));

out += base64EncodeChars.charAt((c2 & 0xF) << 2);

out += "=";

break;

}

c3 = str.charCodeAt(i++);

out += base64EncodeChars.charAt(c1 >> 2);

out += base64EncodeChars.charAt(((c1 & 0x3)<< 4) | ((c2 & 0xF0) >> 4));

out += base64EncodeChars.charAt(((c2 & 0xF) << 2) | ((c3 & 0xC0) >>6));

out += base64EncodeChars.charAt(c3 & 0x3F);

}

return out;

}

function base64decode(str) {

var c1, c2, c3, c4;

var i, len, out;

len = str.length;

i = 0;

out = "";

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;

out += String.fromCharCode((c1 << 2) | ((c2 & 0x30) >> 4));

/* c3 */

do {

c3 = str.charCodeAt(i++) & 0xff;

if(c3 == 61)

return out;

c3 = base64DecodeChars[c3];

} while(i < len && c3 == -1);

if(c3 == -1)

break;

out += String.fromCharCode(((c2 & 0XF) << 4) | ((c3 & 0x3C) >> 2));

/* c4 */

do {

c4 = str.charCodeAt(i++) & 0xff;

if(c4 == 61)

return out;

c4 = base64DecodeChars[c4];

} while(i < len && c4 == -1);

if(c4 == -1)

break;

out += String.fromCharCode(((c3 & 0x03) << 6) | c4);

}

return out;

}

</script>

================================================================================

以下代码可以加密或处理UTF字符串：

以及实例：

<tr>

<td>

var base64EncodeChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

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, 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)

{

out += base64EncodeChars.charAt(c1 >> 2);

out += base64EncodeChars.charAt(((c1 & 0x3)<< 4) | ((c2 & 0xF0) >> 4));

out += base64EncodeChars.charAt((c2 & 0xF) << 2);

out += "=";

break;

}

c3 = str.charCodeAt(i++);

out += base64EncodeChars.charAt(c1 >> 2);

out += base64EncodeChars.charAt(((c1 & 0x3)<< 4) | ((c2 & 0xF0) >> 4));

out += base64EncodeChars.charAt(((c2 & 0xF) << 2) | ((c3 & 0xC0) >>6));

out += base64EncodeChars.charAt(c3 & 0x3F);

}

return out;

}

function base64decode(str) {

var c1, c2, c3, c4;

var i, len, out;

len = str.length;

i = 0;

out = "";

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;

out += String.fromCharCode((c1 << 2) | ((c2 & 0x30) >> 4));

/* c3 */

do {

c3 = str.charCodeAt(i++) & 0xff;

if(c3 == 61)

return out;

c3 = base64DecodeChars[c3];

} while(i < len && c3 == -1);

if(c3 == -1)

break;

out += String.fromCharCode(((c2 & 0XF) << 4) | ((c3 & 0x3C) >> 2));

/* c4 */

do {

c4 = str.charCodeAt(i++) & 0xff;

if(c4 == 61)

return out;

c4 = base64DecodeChars[c4];

} while(i < len && c4 == -1);

if(c4 == -1)

break;

out += String.fromCharCode(((c3 & 0x03) << 6) | c4);

}

return out;

}

function utf16to8(str) {

var out, i, len, c;

out = "";

len = str.length;

for(i = 0; i < len; i++) {

c = str.charCodeAt(i);

if ((c >= 0x0001) && (c <= 0x007F)) {

out += str.charAt(i);

} else if (c > 0x07FF) {

out += String.fromCharCode(0xE0 | ((c >> 12) & 0x0F));

out += String.fromCharCode(0x80 | ((c >> 6) & 0x3F));

out += String.fromCharCode(0x80 | ((c >> 0) & 0x3F));

} else {

out += String.fromCharCode(0xC0 | ((c >> 6) & 0x1F));

out += String.fromCharCode(0x80 | ((c >> 0) & 0x3F));

}

return out;

}

function utf8to16(str) {

var out, i, len, c;

var char2, char3;

out = "";

len = str.length;

i = 0;

while(i < len) {

c = str.charCodeAt(i++);

switch(c >> 4)

{

case 0: case 1: case 2: case 3: case 4: case 5: case 6: case 7:

// 0xxxxxxx

out += str.charAt(i-1);

break;

case 12: case 13:

// 110x xxxx 10xx xxxx

char2 = str.charCodeAt(i++);

out += String.fromCharCode(((c & 0x1F) << 6) | (char2 & 0x3F));

break;

case 14:

// 1110 xxxx 10xx xxxx 10xx xxxx

char2 = str.charCodeAt(i++);

char3 = str.charCodeAt(i++);

out += String.fromCharCode(((c & 0x0F) << 12) |

((char2 & 0x3F) << 6) |

((char3 & 0x3F) << 0));

break;

}

return out;

}

function doit() {

var f = document.f

f.output.value = base64encode(f.source.value)

f.decode.value = base64decode(f.output.value)

}

</script>

<H1 align="center">Base64编码加密

</H1>

原码<BR>

Base64 encode<BR>

Base64 decode<BR>

</FORM>

</td>

</tr>

</table>

C#实现BASE64加密、解密算法

自己完成算法实现

方法一：　/// <summary>

/// Base64加密

/// </summary>

/// <param name="Message"></param>

/// <returns></returns>

public string Base64Code(string Message)

{

char[] Base64Code = new char[]{'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T',

'U','V','W','X','Y','Z','a','b','c','d','e','f','g','h','i','j','k','l','m','n',

'o','p','q','r','s','t','u','v','w','x','y','z','0','1','2','3','4','5','6','7',

'8','9','+','/','='};

byte empty = (byte)0;

System.Collections.ArrayList byteMessage = new System.Collections.ArrayList(System.Text.Encoding.Default.GetBytes(Message));

System.Text.StringBuilder outmessage;

int messageLen = byteMessage.Count;

//将字符分成3个字节一组，如果不足，则以0补齐

int page = messageLen / 3;

int use = 0;

if ((use = messageLen % 3) > 0)

{

for (int i = 0; i < 3 - use; i++)

byteMessage.Add(empty);

page++;

}

//将3个字节的每组字符转换成4个字节一组的。3个一组，一组一组变成4个字节一组

//方法是：转换成ASCII码，按顺序排列24 位数据，再把这24位数据分成4组，即每组6位。再在每组的的最高位前补两个0凑足一个字节。

outmessage = new System.Text.StringBuilder(page * 4);

for (int i = 0; i < page; i++)

{

//取一组3个字节的组

byte[] instr = new byte[3];

instr[0] = (byte)byteMessage[i * 3];

instr[1] = (byte)byteMessage[i * 3 + 1];

instr[2] = (byte)byteMessage[i * 3 + 2];

//六个位为一组，补0变成4个字节

int[] outstr = new int[4];

//第一个输出字节：取第一输入字节的前6位，并且在高位补0，使其变成8位（一个字节）

outstr[0] = instr[0] >> 2;

//第二个输出字节：取第一输入字节的后2位和第二个输入字节的前4位（共6位），并且在高位补0，使其变成8位（一个字节）

outstr[1] = ((instr[0] & 0x03) << 4) ^ (instr[1] >> 4);

//第三个输出字节：取第二输入字节的后4位和第三个输入字节的前2位（共6位），并且在高位补0，使其变成8位（一个字节）

if (!instr[1].Equals(empty))

outstr[2] = ((instr[1] & 0x0f) << 2) ^ (instr[2] >> 6);

else

outstr[2] = 64;

//第四个输出字节：取第三输入字节的后6位，并且在高位补0，使其变成8位（一个字节）

if (!instr[2].Equals(empty))

outstr[3] = (instr[2] & 0x3f);

else

outstr[3] = 64;

outmessage.Append(Base64Code[outstr[0]]);

outmessage.Append(Base64Code[outstr[1]]);

outmessage.Append(Base64Code[outstr[2]]);

outmessage.Append(Base64Code[outstr[3]]);

}

return outmessage.ToString();

}

/// <summary>

/// Base64解密

/// </summary>

/// <param name="Message"></param>

/// <returns></returns>

public string Base64Decode(string Message)

{

if ((Message.Length % 4) != 0)

{

throw new ArgumentException("不是正确的BASE64编码，请检查。", "Message");

}

if (!System.Text.RegularExpressions.Regex.IsMatch(Message, "^[A-Z0-9/+=]*$", System.Text.RegularExpressions.RegexOptions.IgnoreCase))

{

throw new ArgumentException("包含不正确的BASE64编码，请检查。", "Message");

}

string Base64Code = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";

int page = Message.Length / 4;

System.Collections.ArrayList outMessage = new System.Collections.ArrayList(page * 3);

char[] message = Message.ToCharArray();

for (int i = 0; i < page; i++)

{

byte[] instr = new byte[4];

instr[0] = (byte)Base64Code.IndexOf(message[i * 4]);

instr[1] = (byte)Base64Code.IndexOf(message[i * 4 + 1]);

instr[2] = (byte)Base64Code.IndexOf(message[i * 4 + 2]);

instr[3] = (byte)Base64Code.IndexOf(message[i * 4 + 3]);

byte[] outstr = new byte[3];

outstr[0] = (byte)((instr[0] << 2) ^ ((instr[1] & 0x30) >> 4));

if (instr[2] != 64)

{

outstr[1] = (byte)((instr[1] << 4) ^ ((instr[2] & 0x3c) >> 2));

}

else

{

outstr[2] = 0;

}

if (instr[3] != 64)

{

outstr[2] = (byte)((instr[2] << 6) ^ instr[3]);

}

else

{

outstr[2] = 0;

}

outMessage.Add(outstr[0]);

if (outstr[1] != 0)

outMessage.Add(outstr[1]);

if (outstr[2] != 0)

outMessage.Add(outstr[2]);

}

byte[] outbyte = (byte[])outMessage.ToArray(Type.GetType("System.Byte"));

return System.Text.Encoding.Default.GetString(outbyte);

}

直接使用.NET中的的库类函数

方法二：

/// <summary>

/// Base64加密

/// </summary>

/// <param name="Message"></param>

/// <returns></returns>

public string Base64Code(string Message)

{

byte[] bytes = Encoding.Default.GetBytes(Message);

return Convert.ToBase64String(bytes);

}

/// <summary>

/// Base64解密

/// </summary>

/// <param name="Message"></param>

/// <returns></returns>

public string Base64Decode(string Message)

{

byte[] bytes = Convert.FromBase64String(Message);

return Encoding.Default.GetString(bytes);

}

Base64-MIME

在MIME格式的电子邮件中，base64可以用来将binary的字节序列数据编码成ASCII字符序列构成的文本。使用时，在传输编码方式中指定base64。使用的字符包括大小写字母各26个，加上10个数字，和加号“+”，斜杠“/”，一共64个字符，等号“=”用来作为后缀用途。

完整的base64定义可见 RFC1421和 RFC2045。编码后的数据比原始数据略长，为原来的4/3。在电子邮件中，根据RFC822规定，每76个字符，还需要加上一个回车换行。可以估算编码后数据长度大约为原长的135.1%。

转换的时候，将三个byte的数据，先后放入一个24bit的缓冲区中，先来的byte占高位。数据不足3byte的话，于缓冲区中剩下的Bit用0补足。然后，每次取出6个bit，按照其值选择ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/中的字符作为编码后的输出。不断进行，直到全部输入数据转换完成。

如果最后剩下两个输入数据，在编码结果后加1个“=”；如果最后剩下一个输入数据，编码结果后加2个“=”；如果没有剩下任何数据，就什么都不要加，这样才可以保证资料还原的正确性。

举例来说，一段引用自Thomas Hobbes's Leviathan的文句：

Man is distinguished, not only by his reason, but by this singular passion from other animals, which is a lust of the mind, that by a perseverance of delight in the continued and indefatigable generation of knowledge, exceeds the short vehemence of any carnal pleasure.

经过base64编码之后变成：

TWFuIGlzIGRpc3Rpbmd1aXNoZWQsIG5vdCBvbmx5IGJ5IGhpcyByZWFzb24sIGJ1dCBieSB0aGlz

IHNpbmd1bGFyIHBhc3Npb24gZnJvbSBvdGhlciBhbmltYWxzLCB3aGljaCBpcyBhIGx1c3Qgb2Yg

dGhlIG1pbmQsIHRoYXQgYnkgYSBwZXJzZXZlcmFuY2Ugb2YgZGVsaWdodCBpbiB0aGUgY29udGlu

dWVkIGFuZCBpbmRlZmF0aWdhYmxlIGdlbmVyYXRpb24gb2Yga25vd2xlZGdlLCBleGNlZWRzIHRo

ZSBzaG9ydCB2ZWhlbWVuY2Ugb2YgYW55IGNhcm5hbCBwbGVhc3VyZS4=

词条	base64
释义	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 Persistence系统Hibernate中，就采用了Base64来将一个较长的唯一标识符（一般为128-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。标准的Base64(简介规则转换表举例) 在URL中的应用在下载软件中加密下载地址的原理 PHP中的解密下载地址的实现 VB版的Base64编码函数定义 JS版的Base64编码函数定义 JS实现BASE64加密、解密算法 C#实现BASE64加密、解密算法(自己完成算法实现直接使用.NET中的的库类函数) Base64-MIME 标准的Base64 简介标准的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（38 = 46 = 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。规则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）转换表 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 52 0 2 C 19 T 36 k 53 1 3 D 20 U 37 l 54 2 4 E 21 V 38 m 55 3 5 F 22 W 39 n 56 4 6 G 23 X 40 o 57 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 索引　对应字符　索引　对应字符　索引　对应字符　索引　对应字符 0　A　17　R　34　i　51　z 1　B　18　S　35　j　52　0 2　C　19　T　36　k　53　1 3　D　20　U　37　l　54　2 4　E　21　V　38　m　55　3 5　F　22　W　39　n　56　4 6　G　23　X　40　o　57　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　　 15　P　32　g　49　x　　 16　Q　33　h　50　y　　举例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Base64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Base64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。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 Persistence系统Hibernate中，就采用了Base64来将一个较长的唯一标识符（一般为128-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://QUFodHRwOi8vd3d3LmJhaWR1LmNvbS9pbWcvc3NsbTFfbG9nby5naWZaWg== 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www.baidu.com/img/sslm1_logo.gif变成 AAwww.baidu.com/img/sslm1_logo.gifZZ 二、对新的字符串进行Base64编码如AAwww.baidu.com/img/sslm1_logo.gifZZ用Base64编码得到 QUF3d3cuYmFpZHUuY29tL2ltZy9zc2xtMV9sb2dvLmdpZlpa 三、在上面得到的字符串前加上“thunder://”就成了 thunder://QUF3d3cuYmFpZHUuY29tL2ltZy9zc2xtMV9sb2dvLmdpZlpa 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($button=="迅雷地址->普通地址") echo substr(mb_convert_encoding(base64_decode(str_ireplace("thunder://","",$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".$txt1."ZZ"); if($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($txt2); if($button=="FlashGet地址->普通地址") echo str_ireplace("[FLASHGET]","",base64_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> 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@earthlink.net) ' ' 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 Byte lWorkspaceCounter = LBound(bytWorkspace) For lInputCounter = LBound(bytInput) To UBound(bytInput) bytInput(lInputCounter) = m_bytReverseIndex(bytInput(lInputCounter)) Next lInputCounter For lInputCounter = LBound(bytInput) To (UBound(bytInput) - ((UBound(bytInput) Mod 8) + 8)) Step 8 bytWorkspace(lWorkspaceCounter) = (bytInput(lInputCounter) * k_bytShift2) + (bytInput(lInputCounter + 2) \\ k_bytShift4) bytWorkspace(lWorkspaceCounter + 1) = ((bytInput(lInputCounter + 2) And k_bytMask2) * k_bytShift4) + (bytInput(lInputCounter + 4) \\ k_bytShift2) bytWorkspace(lWorkspaceCounter + 2) = ((bytInput(lInputCounter + 4) And 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) And 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) And k_bytMask2) * k_bytShift4) + (bytInput(lInputCounter + 4) \\ k_bytShift2) bytWorkspace(lWorkspaceCounter + 2) = ((bytInput(lInputCounter + 4) And 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 = lWorkspaceCounter + 1 CopyMemory VarPtr(bytResult(LBound(bytResult))), VarPtr(bytWorkspace(LBound(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 Byte End If lWorkspaceCounter = LBound(bytWorkspace) For lCounter = LBound(bytInput) To (UBound(bytInput) - ((UBound(bytInput) Mod 3) + 3)) Step 3 bytWorkspace(lWorkspaceCounter) = m_bytIndex((bytInput(lCounter) \\ k_bytShift2)) 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_bytShift2)) bytWorkspace(lWorkspaceCounter + 2) = m_bytIndex((bytInput(lCounter) And k_bytMask1) * k_bytShift4) bytWorkspace(lWorkspaceCounter + 4) = k_bytEqualSign bytWorkspace(lWorkspaceCounter + 6) = k_bytEqualSign Case 1: bytWorkspace(lWorkspaceCounter) = m_bytIndex((bytInput(lCounter) \\ k_bytShift2)) 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_bytShift2)) 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$(0)) - 1) Else bytCrLf(0) = 13 bytCrLf(1) = 0 bytCrLf(2) = 10 bytCrLf(3) = 0 ReDim bytResult(LBound(bytWorkspace) To UBound(bytWorkspace)) lpWorkSpace = VarPtr(bytWorkspace(LBound(bytWorkspace))) lpResult = VarPtr(bytResult(LBound(bytResult))) lpCrLf = VarPtr(bytCrLf(LBound(bytCrLf))) lCompleteLines = Fix(lWorkspaceCounter / k_lMaxBytesPerLine) For lLineCounter = 0 To lCompleteLines CopyMemory lpResult, lpWorkSpace, k_lMaxBytesPerLine lpWorkSpace = lpWorkSpace + k_lMaxBytesPerLine lpResult = lpResult + k_lMaxBytesPerLine CopyMemory lpResult, lpCrLf, 4& lpResult = lpResult + 4& Next lLineCounter lBytesRemaining = lWorkspaceCounter - (lCompleteLines * k_lMaxBytesPerLine) If lBytesRemaining > 0 Then CopyMemory lpResult, lpWorkSpace, lBytesRemaining EncodeArray64 = Left$(bytResult, InStr(1, bytResult, Chr$(0)) - 1) End If Exit Function ErrorHandler: Erase bytResult EncodeArray64 = bytResult End Function Private Sub Class_Initialize() 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(13) = 78 'Asc("N") 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(51) = 122 'Asc("z") 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(90) = 25 'Asc("Z") 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("+") m_bytReverseIndex(47) = 63 'Asc("/") End Sub JS版的Base64编码函数定义 var base64EncodeChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"; 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 & 0xC0) >>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 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/="; 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 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"; 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) { out += base64EncodeChars.charAt(c1 >> 2); out += base64EncodeChars.charAt(((c1 & 0x3)<< 4) \| ((c2 & 0xF0) >> 4)); out += base64EncodeChars.charAt((c2 & 0xF) << 2); out += "="; break; } c3 = str.charCodeAt(i++); out += base64EncodeChars.charAt(c1 >> 2); out += base64EncodeChars.charAt(((c1 & 0x3)<< 4) \| ((c2 & 0xF0) >> 4)); out += base64EncodeChars.charAt(((c2 & 0xF) << 2) \| ((c3 & 0xC0) >>6)); out += base64EncodeChars.charAt(c3 & 0x3F); } return out; } function base64decode(str) { var c1, c2, c3, c4; var i, len, out; len = str.length; i = 0; out = ""; 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; out += String.fromCharCode((c1 << 2) \| ((c2 & 0x30) >> 4)); / c3 / do { c3 = str.charCodeAt(i++) & 0xff; if(c3 == 61) return out; c3 = base64DecodeChars[c3]; } while(i < len && c3 == -1); if(c3 == -1) break; out += String.fromCharCode(((c2 & 0XF) << 4) \| ((c3 & 0x3C) >> 2)); / c4 / do { c4 = str.charCodeAt(i++) & 0xff; if(c4 == 61) return out; c4 = base64DecodeChars[c4]; } while(i < len && c4 == -1); if(c4 == -1) break; out += String.fromCharCode(((c3 & 0x03) << 6) \| c4); } return out; } </script> ================================================================================ ================================================================================ ================================================================================ 以下代码可以加密或处理UTF字符串：以及实例： <table width="773" border="0" align="center" cellpadding="0" cellspacing="0"> <tr> <td> <script language=javascript> var base64EncodeChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"; 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) { out += base64EncodeChars.charAt(c1 >> 2); out += base64EncodeChars.charAt(((c1 & 0x3)<< 4) \| ((c2 & 0xF0) >> 4)); out += base64EncodeChars.charAt((c2 & 0xF) << 2); out += "="; break; } c3 = str.charCodeAt(i++); out += base64EncodeChars.charAt(c1 >> 2); out += base64EncodeChars.charAt(((c1 & 0x3)<< 4) \| ((c2 & 0xF0) >> 4)); out += base64EncodeChars.charAt(((c2 & 0xF) << 2) \| ((c3 & 0xC0) >>6)); out += base64EncodeChars.charAt(c3 & 0x3F); } return out; } function base64decode(str) { var c1, c2, c3, c4; var i, len, out; len = str.length; i = 0; out = ""; 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; out += String.fromCharCode((c1 << 2) \| ((c2 & 0x30) >> 4)); / c3 / do { c3 = str.charCodeAt(i++) & 0xff; if(c3 == 61) return out; c3 = base64DecodeChars[c3]; } while(i < len && c3 == -1); if(c3 == -1) break; out += String.fromCharCode(((c2 & 0XF) << 4) \| ((c3 & 0x3C) >> 2)); / c4 / do { c4 = str.charCodeAt(i++) & 0xff; if(c4 == 61) return out; c4 = base64DecodeChars[c4]; } while(i < len && c4 == -1); if(c4 == -1) break; out += String.fromCharCode(((c3 & 0x03) << 6) \| c4); } return out; } function utf16to8(str) { var out, i, len, c; out = ""; len = str.length; for(i = 0; i < len; i++) { c = str.charCodeAt(i); if ((c >= 0x0001) && (c <= 0x007F)) { out += str.charAt(i); } else if (c > 0x07FF) { out += String.fromCharCode(0xE0 \| ((c >> 12) & 0x0F)); out += String.fromCharCode(0x80 \| ((c >> 6) & 0x3F)); out += String.fromCharCode(0x80 \| ((c >> 0) & 0x3F)); } else { out += String.fromCharCode(0xC0 \| ((c >> 6) & 0x1F)); out += String.fromCharCode(0x80 \| ((c >> 0) & 0x3F)); } } return out; } function utf8to16(str) { var out, i, len, c; var char2, char3; out = ""; len = str.length; i = 0; while(i < len) { c = str.charCodeAt(i++); switch(c >> 4) { case 0: case 1: case 2: case 3: case 4: case 5: case 6: case 7: // 0xxxxxxx out += str.charAt(i-1); break; case 12: case 13: // 110x xxxx 10xx xxxx char2 = str.charCodeAt(i++); out += String.fromCharCode(((c & 0x1F) << 6) \| (char2 & 0x3F)); break; case 14: // 1110 xxxx 10xx xxxx 10xx xxxx char2 = str.charCodeAt(i++); char3 = str.charCodeAt(i++); out += String.fromCharCode(((c & 0x0F) << 12) \| ((char2 & 0x3F) << 6) \| ((char3 & 0x3F) << 0)); break; } } return out; } function doit() { var f = document.f f.output.value = base64encode(f.source.value) f.decode.value = base64decode(f.output.value) } </script> <H1 align="center">Base64编码加密 </H1> <FORM NAME="f"> 原码<BR> <TEXTAREA NAME="source" ROWS=4 COLS=60 WRAP="soft"></TEXTAREA><BR><BR> Base64 encode<BR> <TEXTAREA NAME="output" ROWS=4 COLS=60 WRAP="soft"></TEXTAREA><BR><BR> Base64 decode<BR> <TEXTAREA NAME="decode" ROWS=4 COLS=60 WRAP="soft"></TEXTAREA><BR><BR> <INPUT TYPE=BUTTON VALUE="转换" ONCLICK="doit()"> </FORM> </td> </tr> </table> C#实现BASE64加密、解密算法自己完成算法实现方法一：　/// <summary> /// Base64加密 /// </summary> /// <param name="Message"></param> /// <returns></returns> public string Base64Code(string Message) { char[] Base64Code = new char[]{'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T', 'U','V','W','X','Y','Z','a','b','c','d','e','f','g','h','i','j','k','l','m','n', 'o','p','q','r','s','t','u','v','w','x','y','z','0','1','2','3','4','5','6','7', '8','9','+','/','='}; byte empty = (byte)0; System.Collections.ArrayList byteMessage = new System.Collections.ArrayList(System.Text.Encoding.Default.GetBytes(Message)); System.Text.StringBuilder outmessage; int messageLen = byteMessage.Count; //将字符分成3个字节一组，如果不足，则以0补齐 int page = messageLen / 3; int use = 0; if ((use = messageLen % 3) > 0) { for (int i = 0; i < 3 - use; i++) byteMessage.Add(empty); page++; } //将3个字节的每组字符转换成4个字节一组的。3个一组，一组一组变成4个字节一组 //方法是：转换成ASCII码，按顺序排列24 位数据，再把这24位数据分成4组，即每组6位。再在每组的的最高位前补两个0凑足一个字节。 outmessage = new System.Text.StringBuilder(page 4); for (int i = 0; i < page; i++) { //取一组3个字节的组 byte[] instr = new byte[3]; instr[0] = (byte)byteMessage[i * 3]; instr[1] = (byte)byteMessage[i * 3 + 1]; instr[2] = (byte)byteMessage[i * 3 + 2]; //六个位为一组，补0变成4个字节 int[] outstr = new int[4]; //第一个输出字节：取第一输入字节的前6位，并且在高位补0，使其变成8位（一个字节） outstr[0] = instr[0] >> 2; //第二个输出字节：取第一输入字节的后2位和第二个输入字节的前4位（共6位），并且在高位补0，使其变成8位（一个字节） outstr[1] = ((instr[0] & 0x03) << 4) ^ (instr[1] >> 4); //第三个输出字节：取第二输入字节的后4位和第三个输入字节的前2位（共6位），并且在高位补0，使其变成8位（一个字节） if (!instr[1].Equals(empty)) outstr[2] = ((instr[1] & 0x0f) << 2) ^ (instr[2] >> 6); else outstr[2] = 64; //第四个输出字节：取第三输入字节的后6位，并且在高位补0，使其变成8位（一个字节） if (!instr[2].Equals(empty)) outstr[3] = (instr[2] & 0x3f); else outstr[3] = 64; outmessage.Append(Base64Code[outstr[0]]); outmessage.Append(Base64Code[outstr[1]]); outmessage.Append(Base64Code[outstr[2]]); outmessage.Append(Base64Code[outstr[3]]); } return outmessage.ToString(); } /// <summary> /// Base64解密 /// </summary> /// <param name="Message"></param> /// <returns></returns> public string Base64Decode(string Message) { if ((Message.Length % 4) != 0) { throw new ArgumentException("不是正确的BASE64编码，请检查。", "Message"); } if (!System.Text.RegularExpressions.Regex.IsMatch(Message, "^[A-Z0-9/+=]$", System.Text.RegularExpressions.RegexOptions.IgnoreCase)) { throw new ArgumentException("包含不正确的BASE64编码，请检查。", "Message"); } string Base64Code = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/="; int page = Message.Length / 4; System.Collections.ArrayList outMessage = new System.Collections.ArrayList(page 3); char[] message = Message.ToCharArray(); for (int i = 0; i < page; i++) { byte[] instr = new byte[4]; instr[0] = (byte)Base64Code.IndexOf(message[i * 4]); instr[1] = (byte)Base64Code.IndexOf(message[i * 4 + 1]); instr[2] = (byte)Base64Code.IndexOf(message[i * 4 + 2]); instr[3] = (byte)Base64Code.IndexOf(message[i * 4 + 3]); byte[] outstr = new byte[3]; outstr[0] = (byte)((instr[0] << 2) ^ ((instr[1] & 0x30) >> 4)); if (instr[2] != 64) { outstr[1] = (byte)((instr[1] << 4) ^ ((instr[2] & 0x3c) >> 2)); } else { outstr[2] = 0; } if (instr[3] != 64) { outstr[2] = (byte)((instr[2] << 6) ^ instr[3]); } else { outstr[2] = 0; } outMessage.Add(outstr[0]); if (outstr[1] != 0) outMessage.Add(outstr[1]); if (outstr[2] != 0) outMessage.Add(outstr[2]); } byte[] outbyte = (byte[])outMessage.ToArray(Type.GetType("System.Byte")); return System.Text.Encoding.Default.GetString(outbyte); } 直接使用.NET中的的库类函数方法二： /// <summary> /// Base64加密 /// </summary> /// <param name="Message"></param> /// <returns></returns> public string Base64Code(string Message) { byte[] bytes = Encoding.Default.GetBytes(Message); return Convert.ToBase64String(bytes); } /// <summary> /// Base64解密 /// </summary> /// <param name="Message"></param> /// <returns></returns> public string Base64Decode(string Message) { byte[] bytes = Convert.FromBase64String(Message); return Encoding.Default.GetString(bytes); } Base64-MIME 在MIME格式的电子邮件中，base64可以用来将binary的字节序列数据编码成ASCII字符序列构成的文本。使用时，在传输编码方式中指定base64。使用的字符包括大小写字母各26个，加上10个数字，和加号“+”，斜杠“/”，一共64个字符，等号“=”用来作为后缀用途。完整的base64定义可见 RFC1421和 RFC2045。编码后的数据比原始数据略长，为原来的4/3。在电子邮件中，根据RFC822规定，每76个字符，还需要加上一个回车换行。可以估算编码后数据长度大约为原长的135.1%。转换的时候，将三个byte的数据，先后放入一个24bit的缓冲区中，先来的byte占高位。数据不足3byte的话，于缓冲区中剩下的Bit用0补足。然后，每次取出6个bit，按照其值选择ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/中的字符作为编码后的输出。不断进行，直到全部输入数据转换完成。如果最后剩下两个输入数据，在编码结果后加1个“=”；如果最后剩下一个输入数据，编码结果后加2个“=”；如果没有剩下任何数据，就什么都不要加，这样才可以保证资料还原的正确性。举例来说，一段引用自Thomas Hobbes's Leviathan的文句： Man is distinguished, not only by his reason, but by this singular passion from other animals, which is a lust of the mind, that by a perseverance of delight in the continued and indefatigable generation of knowledge, exceeds the short vehemence of any carnal pleasure. 经过base64编码之后变成： TWFuIGlzIGRpc3Rpbmd1aXNoZWQsIG5vdCBvbmx5IGJ5IGhpcyByZWFzb24sIGJ1dCBieSB0aGlz IHNpbmd1bGFyIHBhc3Npb24gZnJvbSBvdGhlciBhbmltYWxzLCB3aGljaCBpcyBhIGx1c3Qgb2Yg dGhlIG1pbmQsIHRoYXQgYnkgYSBwZXJzZXZlcmFuY2Ugb2YgZGVsaWdodCBpbiB0aGUgY29udGlu dWVkIGFuZCBpbmRlZmF0aWdhYmxlIGdlbmVyYXRpb24gb2Yga25vd2xlZGdlLCBleGNlZWRzIHRo ZSBzaG9ydCB2ZWhlbWVuY2Ugb2YgYW55IGNhcm5hbCBwbGVhc3VyZS4=
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