[]
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
如变成
AAZZ
二、对新的字符串进行Base64编码
如AAZZ用Base64编码得到
QUFodHRwOi8vd3d3LmJhaWR1LmNvbS9pbWcvc3NsbTFfbG9nby5naWZaWg==
三、在上面得到的字符串前加上“thunder://”就成了
thunder://QUFodHRwOi8vd3d3LmJhaWR1LmNvbS9pbWcvc3NsbTFfbG9nby5naWZaWg==
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
$txt1=trim($_POST['text1']);
$txt2=trim($_POST['text2']);
$txt3=trim($_POST['text3']);
$button=$_POST['button'];
?>
迅雷和FlashGet,QQ旋风地址 地址转换工具
[]
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：
================================================================================
================================================================================
================================================================================
以下代码可以加密或处理UTF字符串：
以及实例：
[]
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=
