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个字节变成4个字节。
②每76个字符加一个换行符。
③.最后的结束符也要处理。
例子1
转换前 11111111, 11111111, 11111111 (二进制)
转换后 00111111, 00111111, 00111111, 00111111 (二进制)
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
索引 | 对应字符 |
0 | A |
1 | B |
2 | C |
3 | D |
4 | E |
5 | F |
6 | G |
7 | H |
8 | I |
9 | J |
10 | K |
11 | L |
12 | M |
13 | N |
14 | O |
15 | P |
16 | Q |
17 | R |
18 | S |
19 | T |
20 | U |
21 | V |
22 | W |
23 | X |
24 | Y |
25 | Z |
26 | a |
27 | b |
28 | c |
29 | d |
30 | e |
31 | f |
32 | g |
33 | h |
34 | i |
35 | j |
36 | k |
37 | l |
38 | m |
39 | n |
40 | o |
41 | p |
42 | q |
43 | r |
44 | s |
45 | t |
46 | u |
47 | v |
48 | w |
49 | x |
50 | y |
51 | z |
52 | 0 |
53 | 1 |
54 | 2 |
55 | 3 |
56 | 4 |
57 | 5 |
58 | 6 |
59 | 7 |
60 | 8 |
61 | 9 |
62 | + |
63 | / |
例子2
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,有关MIME的RFC还有很多,如果需要详细情况请自行查找。)
第一个字节,根据源字节的第一个字节处理。
规则:源第一字节右移两位,去掉低2位,高2位补零。
既:00+高6位
第二个字节,根据源字节的第一个字节和第二个字节联合处理。
规则如下,第一个字节高6位去掉然后左移四位,第二个字节右移四位
即:源第一字节低2位+源第2字节高4位
第三个字节,根据源字节的第二个字节和第三个字节联合处理,
规则第二个字节去掉高4位并左移两位(得高6位),第三个字节右移6位并去掉高6位(得低2位),相加即可
第四个字节,规则,源第三字节去掉高2位即可
//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。
//然后将第一个字符与0x03(00000011)进行与(&)操作并左移4位,接着第二个字符右移4位与前者相或(|),即获得第二个目标字符。
//再将第二个字符与0x0f(00001111)进行与(&)操作并左移2位,接着第三个字符右移6位与前者相或(|),获得第三个目标字符。
//最后将第三个字符与0x3f(00111111)进行与(&)操作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。
原文的字节数量应该是3的倍数,如果这个条件不能满足的话,具体的解决办法是这样的:原文剩余的字节根据编码规则继续单独转(1变2,2变3;不够的位数用0补全),再用=号补满4个字节。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。因为一个原字节至少会变成两个目标字节,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)。如果是1的话,转成2个Base64编码字符,为了让Base64编码是4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。
原理
转码过程例子:
3*8=4*6
内存1个字节占8位
转前: s 1 3
先转成ascii:对应 115 49 51
2进制:01110011 00110001 00110011
6个一组(4组) 011100110011000100110011
然后才有后面的 011100 110011 000100 110011
然后计算机一个字节占8位,不够就自动补两个高位0了
所以有了高位补0
科学计算器输入 00011100 00110011 00000100 00110011
得到 28 51 4 51
查对下照表 c z E z
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。
其实迅雷的“专用地址”也是用Base64"加密"的,其过程如下:
一、在地址的前后分别添加AA和ZZ
二、对新的字符串进行Base64编码
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
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来将一个较长的一个标识符(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,它不仅在末尾去掉填充的'='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)。
其他应用
Mozilla Thunderbird和Evolution用Base64来保密电子邮件密码
Base64 也会经常用作一个简单的“加密”来保护某些数据,而真正的加密通常都比较繁琐。
垃圾讯息传播者用Base64来避过反垃圾邮件工具,因为那些工具通常都不会翻译Base64的讯息。
在LDIF档案,Base64用作编码字串。
代码实现
JavaScript版
1 | if (!Shotgun) |
2 | var Shotgun = {}; |
3 | if (!Shotgun.Js) |
4 | Shotgun.Js = {}; |
5 | Shotgun.Js.Base64 = { |
6 | _table: [ |
7 | 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', |
8 | 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', |
9 | 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', |
10 | 'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '+', '/' |
11 | ], |
12 | |
13 | encode: function (bin) { |
14 | var codes = []; |
15 | var un = 0; |
16 | un = bin.length % 3; |
17 | if (un == 1) |
18 | bin.push(0, 0); |
19 | else if (un == 2) |
20 | bin.push(0); |
21 | for (var i = 2; i < bin.length; i += 3) { |
22 | var c = bin[i - 2] << 16; |
23 | c |= bin[i - 1] << 8; |
24 | c |= bin[i]; |
25 | codes.push(this._table[c >> 18 & 0x3f]); |
26 | codes.push(this._table[c >> 12 & 0x3f]); |
27 | codes.push(this._table[c >> 6 & 0x3f]); |
28 | codes.push(this._table[c & 0x3f]); |
29 | } |
30 | if (un >= 1) { |
31 | codes[codes.length - 1] = "="; |
32 | bin.pop(); |
33 | } |
34 | if (un == 1) { |
35 | codes[codes.length - 2] = "="; |
36 | bin.pop(); |
37 | } |
38 | return codes.join(""); |
39 | }, |
40 | decode: function (base64Str) { |
41 | var i = 0; |
42 | var bin = []; |
43 | var x = 0, code = 0, eq = 0; |
44 | while (i < base64Str.length) { |
45 | var c = base64Str.charAt(i++); |
46 | var idx = this._table.indexOf(c); |
47 | if (idx == -1) { |
48 | switch (c) { |
49 | case '=': idx = 0; eq++; break; |
50 | case ' ': |
51 | case '
': |
52 | case "
": |
53 | case ' ': |
54 | continue; |
55 | default: |
56 | throw { "message": "u0062u0061u0073u0065u0036u0034u002Eu0074u0068u0065u002Du0078u002Eu0063u006Eu0020u0045u0072u0072u006Fu0072u003Au65E0u6548u7F16u7801uFF1A" + c }; |
57 | } |
58 | } |
59 | if (eq > 0 && idx != 0) |
60 | throw { "message": "u0062u0061u0073u0065u0036u0034u002Eu0074u0068u0065u002Du0078u002Eu0063u006Eu0020u0045u0072u0072u006Fu0072u003Au7F16u7801u683Cu5F0Fu9519u8BEFuFF01" }; |
61 | |
62 | code = code << 6 | idx; |
63 | if (++x != 4) |
64 | continue; |
65 | bin.push(code >> 16); |
66 | bin.push(code >> 8 & 0xff); |
67 | bin.push(code & 0xff) |
68 | code = x = 0; |
69 | } |
70 | if (code != 0) |
71 | throw { "message": "u0062u0061u0073u0065u0036u0034u002Eu0074u0068u0065u002Du0078u002Eu0063u006Eu0020u0045u0072u0072u006Fu0072u003Au7F16u7801u6570u636Eu957Fu5EA6u9519u8BEF" }; |
72 | if (eq == 1) |
73 | bin.pop(); |
74 | else if (eq == 2) { |
75 | bin.pop(); |
76 | bin.pop(); |
77 | } else if (eq > 2) |
78 | throw { "message": "u0062u0061u0073u0065u0036u0034u002Eu0074u0068u0065u002Du0078u002Eu0063u006Eu0020u0045u0072u0072u006Fu0072u003Au7F16u7801u683Cu5F0Fu9519u8BEFuFF01" }; |
79 | |
80 | return bin; |
81 | } |
82 | }; |
BASH版
1 | base64Table=(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 + /); |
2 | |
3 | function str2binary() { |
4 | idx=0; |
5 | for((i=0; i<${#str}; i++)); do |
6 | dividend=$(printf "%d" "'${str:i:1}"); |
7 | for((j=0;j<8;j++)); do |
8 | let idx=8*i+7-j; |
9 | let bin[$idx]=$dividend%2; |
10 | dividend=$dividend/2; |
11 | done; |
12 | done; |
13 | let idx=${#str}*8; |
14 | for((i=0; i<appendEqualCnt*2; i++)); do |
15 | let bin[$idx]=0; |
16 | let idx++; |
17 | done; |
18 | } |
19 | function calcBase64() { |
20 | for((i=0; i<${#bin[*]}/6; i++)); do |
21 | sum=0; |
22 | for((j=0; j<6; j++)); do |
23 | let idx=i*6+j; |
24 | let n=6-1-j; |
25 | let sum=sum+${bin[$idx]}*2**n; |
26 | done; |
27 | echo -n ${base64Table[$sum]}; |
28 | done |
29 | } |
30 | |
31 | declare -a bin |
32 | function base64Encode() { |
33 | read -p "please enter ASCII string:" str; |
34 | let appendZero=${#str}*8%6; |
35 | let bits=${#str}*8; |
36 | appendEqualCnt=0; |
37 | if [[ $appendZero -ne 0 ]]; then |
38 | let appendEqualCnt=(6-$appendZero)/2; |
39 | fi |
40 | str2binary; |
41 | calcBase64; |
42 | if [[ $appendEqualCnt -eq 2 ]]; then |
43 | echo -n "=="; |
44 | elif [[ $appendEqualCnt -eq 1 ]]; then |
45 | echo -n "="; |
46 | fi |
47 | echo; |
48 | |
49 | } |
Java版
1 | import java.util.Base64; |
2 | 对于标准的Base64: |
3 | 加密为字符串使用Base64.getEncoder().encodeToString(); |
4 | 加密为字节数组使用Base64.getEncoder().encode(); |
5 | 解密使用Base64.getDecoder().decode(); |
6 | 对于URL安全或MIME的Base64,只需将上述getEncoder()getDecoder()更换为getUrlEncoder()getUrlDecoder() |
7 | 或getMimeEncoder()和getMimeDecoder()即可。 |
PHP版
[下列代码仅在GBK中实现,UTF8代码请把if($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]
1 | <?php |
2 | $txt1=trim($_POST['text1']); |
3 | $txt2=trim($_POST['text2']); |
4 | $txt3=trim($_POST['text3']); |
5 | $button=$_POST['button']; |
6 | ?> |
7 | <!DOCTYPEHTMLPUBLIC"-//W3C//DTDHTML4.0Transitional//EN"> |
8 | <html> |
9 | <head> |
10 | <title>迅雷和FlashGet,QQ旋风地址地址转换工具</title> |
11 | <metahttp-equiv="Content-Type"content="text/html;charset=gb2312"> |
12 | <metacontent="迅雷,FlashGet,地址转换,"name="keywords"> |
13 | </head> |
14 | <body> |
15 | <formname="form1"method="post"action=""> |
16 | <hrsize="1"> |
17 | <h3>迅雷转换</h3> |
18 | <P>转换地址: |
19 | <inputname="text1"value="<?phpecho$txt1;?>"type="text"style="width:516px;"/></P> |
20 | <P>转换后的: |
21 | <inputtype="text"value="<?php |
22 | if($button=="普通地址->迅雷地址")echo"thunder://".base64_encode("AA".$txt1."ZZ"); |
23 | if($button=="迅雷地址->普通地址")echosubstr(base64_decode(str_ireplace("thunder://","",$txt1)),2,-2); |
24 | ?>"style="width:516px;"/></P> |
25 | <P> |
26 | <inputtype="submit"name="button"value="普通地址->迅雷地址"/> |
27 | <inputtype="submit"name="button"value="迅雷地址->普通地址"/></P> |
28 | <h3>FlashGet转换</h3> |
29 | <P>FlashGet地址: |
30 | <inputname="text2"value="<?phpecho$txt2;?>"type="text"style="width:516px;"/></P> |
31 | <P>转换后地址: |
32 | <inputtype="text"value="<?php |
33 | if($button=="普通地址->FlashGet地址")echo"flashget://".base64_encode($txt2); |
34 | if($button=="FlashGet地址->普通地址")echostr_ireplace("[FLASHGET]","",base64_decode(str_ireplace("flashget://","",$txt2))); |
35 | ?>"style="width:516px;"/></P> |
36 | <P> |
37 | <inputtype="submit"value="普通地址->FlashGet地址"name="button"/> |
38 | <inputtype="submit"value="FlashGet地址->普通地址"name="button"/></P> |
39 | <h3>QQ旋风转换</h3> |
40 | <P>QQ旋风地址: |
41 | <inputname="text3"value="<?phpecho$txt3;?>"type="text"style="width:516px;"/></P> |
42 | <P>转换后地址: |
43 | <inputtype="text"value="<?php |
44 | if($button=="普通地址->QQ旋风")echo"qqdl://".base64_encode($txt3); |
45 | if($button=="QQ旋风->普通地址")echobase64_decode(str_ireplace("qqdl://","",$txt3)); |
46 | ?>"style="width:516px;"/></P> |
47 | <P> |
48 | <inputtype="submit"value="普通地址->QQ旋风"name="button"/> |
49 | <inputtype="submit"value="QQ旋风->普通地址"name="button"/></P> |
50 | </form> |
51 | </body> |
52 | </html> |
VB版
注:其中DigestStrToHexStr为可在程序外部调用加密函数
1 | Option Explicit |
2 | 'B as e64Encoding/DecodingAlgorithm |
3 | 'By:DavidMidkif f(mznull@earthlink.net) |
4 | ' |
5 | 'Thisalgorithmsencodes and decodesdatain to B as e64 |
6 | 'for mat.Thisfor matisextremelymoreefficientthan |
7 | 'Hexadecimalencoding. |
8 | Private m_bytIndex(0 To 63) As Byte |
9 | Private m_bytReverseIndex(0 To 255) As Byte |
10 | Private Const k_bytEqualSign As Byte = 61 |
11 | Private Const k_bytmask1 As Byte = 3 |
12 | Private Const k_bytmask2 As Byte = 15 |
13 | Private Const k_bytmask3 As Byte = 63 |
14 | Private Const k_bytmask4 As Byte = 192 |
15 | Private Const k_bytmask5 As Byte = 240 |
16 | Private Const k_bytmask6 As Byte = 252 |
17 | Private Const k_bytShift2 As Byte = 4 |
18 | Private Const k_bytShift4 As Byte = 16 |
19 | Private Const k_bytShift6 As Byte = 64 |
20 | Private Const k_lMaxBytesPerLine As Long = 152 |
21 | Private Declare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" (ByVal Destination As Long, ByVal Source As Long, ByVal Length As Long) |
22 | Public Function Decode64(sInput As String) As String |
23 | If sInput = "" Then Exit Function |
24 | Decode64 = StrConv(DecodeArray64(sInput), vbUnicode) |
25 | End Function |
26 | Private Function DecodeArray64(sInput As String) As Byte() |
27 | Dim bytInput() As Byte |
28 | Dim bytWorkspace() As Byte |
29 | Dim bytResult() As Byte |
30 | Dim lInputCounter As Long |
31 | Dim lWorkspaceCounter As Long |
32 | bytInput = Replace(Replace(sInput, vbCrLf, ""), "=", "") |
33 | ReDim bytWorkspace(LBound(bytInput) To (UBound(bytInput) * 2)) As Byte |
34 | lWorkspaceCounter = LBound(bytWorkspace) |
35 | For lInputCounter = LBound(bytInput) To UBound(bytInput) |
36 | bytInput(lInputCounter) = m_bytReverseIndex(bytInput(lInputCounter)) |
37 | Next lInputCounter |
38 | For lInputCounter = LBound(bytInput) To (UBound(bytInput) - ((UBound(bytInput) Mod 8) + 8)) Step 8 |
39 | bytWorkspace(lWorkspaceCounter) = (bytInput(lInputCounter) * k_bytShift2) + (bytInput(lInputCounter + 2) k_bytShift4) |
40 | bytWorkspace(lWorkspaceCounter + 1) = ((bytInput(lInputCounter + 2) And k_bytmask2) * k_bytShift4) + (bytInput(lInputCounter + 4) k_bytShift2) |
41 | bytWorkspace(lWorkspaceCounter + 2) = ((bytInput(lInputCounter + 4) And k_bytmask1) * k_bytShift6) + bytInput(lInputCounter + 6) |
42 | lWorkspaceCounter = lWorkspaceCounter + 3 |
43 | Next lInputCounter |
44 | Select Case (UBound(bytInput) Mod 8): |
45 | Case 3: |
46 | bytWorkspace(lWorkspaceCounter) = (bytInput(lInputCounter) * k_bytShift2) + (bytInput(lInputCounter + 2) k_bytShift4) |
47 | Case 5: |
48 | bytWorkspace(lWorkspaceCounter) = (bytInput(lInputCounter) * k_bytShift2) + (bytInput(lInputCounter + 2) k_bytShift4) |
49 | bytWorkspace(lWorkspaceCounter + 1) = ((bytInput(lInputCounter + 2) And k_bytmask2) * k_bytShift4) + (bytInput(lInputCounter + 4) k_bytShift2) |
50 | lWorkspaceCounter = lWorkspaceCounter + 1 |
51 | Case 7: |
52 | bytWorkspace(lWorkspaceCounter) = (bytInput(lInputCounter) * k_bytShift2) + (bytInput(lInputCounter + 2) k_bytShift4) |
53 | bytWorkspace(lWorkspaceCounter + 1) = ((bytInput(lInputCounter + 2) And k_bytmask2) * k_bytShift4) + (bytInput(lInputCounter + 4) k_bytShift2) |
54 | bytWorkspace(lWorkspaceCounter + 2) = ((bytInput(lInputCounter + 4) And k_bytmask1) * k_bytShift6) + bytInput(lInputCounter + 6) |
55 | lWorkspaceCounter = lWorkspaceCounter + 2 |
56 | End Select |
57 | ReDim bytResult(LBound(bytWorkspace) To lWorkspaceCounter) As Byte |
58 | If LBound(bytWorkspace) = 0 Then lWorkspaceCounter = lWorkspaceCounter + 1 |
59 | CopyMemoryVarPtr (bytResult(LBound(bytResult))), VarPtr(bytWorkspace(LBound(bytWorkspace))), lWorkspaceCounter |
60 | DecodeArray64 = bytResult |
61 | End Function |
62 | Public Function Encode64(ByRefsInput As String) As String |
63 | If sInput = "" Then Exit Function |
64 | Dim bytTemp() As Byte |
65 | bytTemp = StrConv(sInput, vbFromUnicode) |
66 | Encode64 = EncodeArray64(bytTemp) |
67 | End Function |
68 | Private Function EncodeArray64(ByRefbytInput() As Byte) As String |
69 | On Error GoTo ErrorHandler |
70 | Dim bytWorkspace() As Byte, bytResult() As Byte |
71 | Dim bytCrLf(0 To 3) As Byte, lCounter As Long |
72 | Dim lWorkspaceCounter As Long, lLineCounter As Long |
73 | Dim lCompleteLines As Long, lBytesRemaining As Long |
74 | Dim lpWorkSpace As Long, lpResult As Long |
75 | Dim lpCrLf As Long |
76 | If UBound(bytInput) < 1024 Then |
77 | ReDim bytWorkspace(LBound(bytInput) To (LBound(bytInput) + 4096)) As Byte |
78 | Else |
79 | ReDim bytWorkspace(LBound(bytInput) To (UBound(bytInput) * 4)) As Byte |
80 | End If |
81 | lWorkspaceCounter = LBound(bytWorkspace) |
82 | For lCounter = LBound(bytInput) To (UBound(bytInput) - ((UBound(bytInput) Mod 3) + 3)) Step 3 |
83 | bytWorkspace(lWorkspaceCounter) = m_bytIndex((bytInput(lCounter) k_bytShift2)) |
84 | bytWorkspace(lWorkspaceCounter + 2) = m_bytIndex(((bytInput(lCounter) And k_bytmask1) * k_bytShift4) + ((bytInput(lCounter + 1)) k_bytShift4)) |
85 | bytWorkspace(lWorkspaceCounter + 4) = m_bytIndex(((bytInput(lCounter + 1) And k_bytmask2) * k_bytShift2) + (bytInput(lCounter + 2) k_bytShift6)) |
86 | bytWorkspace(lWorkspaceCounter + 6) = m_bytIndex(bytInput(lCounter + 2) And k_bytmask3) |
87 | lWorkspaceCounter = lWorkspaceCounter + 8 |
88 | Next lCounter |
89 | Select Case (UBound(bytInput) Mod 3): |
90 | Case 0: |
91 | bytWorkspace(lWorkspaceCounter) = m_bytIndex((bytInput(lCounter) k_bytShift2)) |
92 | bytWorkspace(lWorkspaceCounter + 2) = m_bytIndex((bytInput(lCounter) And k_bytmask1) * k_bytShift4) |
93 | bytWorkspace(lWorkspaceCounter + 4) = k_bytEqualSign |
94 | bytWorkspace(lWorkspaceCounter + 6) = k_bytEqualSign |
95 | Case 1: |
96 | bytWorkspace(lWorkspaceCounter) = m_bytIndex((bytInput(lCounter) k_bytShift2)) |
97 | bytWorkspace(lWorkspaceCounter + 2) = m_bytIndex(((bytInput(lCounter) And k_bytmask1) * k_bytShift4) + ((bytInput(lCounter + 1)) k_bytShift4)) |
98 | bytWorkspace(lWorkspaceCounter + 4) = m_bytIndex((bytInput(lCounter + 1) And k_bytmask2) * k_bytShift2) |
99 | bytWorkspace(lWorkspaceCounter + 6) = k_bytEqualSign |
100 | Case 2: |
101 | bytWorkspace(lWorkspaceCounter) = m_bytIndex((bytInput(lCounter) k_bytShift2)) |
102 | bytWorkspace(lWorkspaceCounter + 2) = m_bytIndex(((bytInput(lCounter) And k_bytmask1) * k_bytShift4) + ((bytInput(lCounter + 1)) k_bytShift4)) |
103 | bytWorkspace(lWorkspaceCounter + 4) = m_bytIndex(((bytInput(lCounter + 1) And k_bytmask2) * k_bytShift2) + ((bytInput(lCounter + 2)) k_bytShift6)) |
104 | bytWorkspace(lWorkspaceCounter + 6) = m_bytIndex(bytInput(lCounter + 2) And k_bytmask3) |
105 | End Select |
106 | lWorkspaceCounter = lWorkspaceCounter + 8 |
107 | If lWorkspaceCounter <= k_lMaxBytesPerLine Then |
108 | EncodeArray64 = Left$(bytWorkspace, InStr(1, bytWorkspace, Chr$(0)) - 1) |
109 | Else |
110 | bytCrLf(0) = 13 |
111 | bytCrLf(1) = 0 |
112 | bytCrLf(2) = 10 |
113 | bytCrLf(3) = 0 |
114 | ReDim bytResult(LBound(bytWorkspace) To UBound(bytWorkspace)) |
115 | lpWorkSpace = VarPtr(bytWorkspace(LBound(bytWorkspace))) |
116 | lpResult = VarPtr(bytResult(LBound(bytResult))) |
117 | lpCrLf = VarPtr(bytCrLf(LBound(bytCrLf))) |
118 | lCompleteLines = Fix(lWorkspaceCounter / k_lMaxBytesPerLine) |
119 | For lLineCounter = 0 To lCompleteLines |
120 | CopyMemorylpResult , lpWorkSpace, k_lMaxBytesPerLine |
121 | lpWorkSpace = lpWorkSpace + k_lMaxBytesPerLine |
122 | lpResult = lpResult + k_lMaxBytesPerLine |
123 | CopyMemorylpResult , lpCrLf, 4& |
124 | lpResult = lpResult + 4& |
125 | Next lLineCounter |
126 | lBytesRemaining = lWorkspaceCounter - (lCompleteLines * k_lMaxBytesPerLine) |
127 | If lBytesRemaining > 0 Then CopyMemorylpResult , lpWorkSpace, lBytesRemaining |
128 | EncodeArray64 = Left$(bytResult, InStr(1, bytResult, Chr$(0)) - 1) |
129 | End If |
130 | Exit Function |
131 | ErrorHandler: |
132 | Er As ebytResult |
133 | EncodeArray64 = bytResult |
134 | End Function |
C#版
1 | 直接使用.NET中的的库类函数 |
2 | 方法: |
3 | ///<summary> |
4 | ///Base64加密 |
5 | ///</summary> |
6 | ///<paramname="Message"></param> |
7 | ///<returns></returns> |
8 | publicstringBase64Code(stringMessage) |
9 | { |
10 | byte[]bytes=Encoding.Default.GetBytes(Message); |
11 | returnConvert.ToBase64String(bytes); |
12 | } |
13 | ///<summary> |
14 | ///Base64解密 |
15 | ///</summary> |
16 | ///<paramname="Message"></param> |
17 | ///<returns></returns> |
18 | publicstringBase64Decode(stringMessage) |
19 | { |
20 | byte[]bytes=Convert.FromBase64String(Message); |
21 | returnEncoding.Default.GetString(bytes); |
22 | } |
python版
1 | def base(string:str)->str: |
2 | oldstr = '' |
3 | newstr = [] |
4 | base = '' |
5 | base64_list = ['A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', |
6 | 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', |
7 | 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', |
8 | 'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '+', '/'] |
9 | #把原始字符串转换为二进制,用bin转换后是0b开头的,所以把b替换了,首位补0补齐8位 |
10 | for i in string: |
11 | oldstr += '{:08}'.format(int(str(bin(ord(i))).replace('0b', ''))) |
12 | #把转换好的二进制按照6位一组分好,最后一组不足6位的后面补0 |
13 | for j in range(0, len(oldstr), 6): |
14 | newstr.append('{:<06}'.format(oldstr[j:j + 6])) |
15 | #在base_list中找到对应的字符,拼接 |
16 | for l in range(len(newstr)): |
17 | base += base64_list[int(newstr[l], 2)] |
18 | #判断base字符结尾补几个‘=’ |
19 | if len(string) % 3 == 1: |
20 | base += '==' |
21 | elif len(string) % 3 == 2: |
22 | base += '=' |
23 | return base |
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=