BASE64编码在C#、Delphi和JavaScript中的实现

一、编码规则
Base64编码的思想是是采用64个基本的ASCII码字符对数据进行重新编码。它将需要编码的数据拆分成字节数组。以3个字节为一组。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。这样就把一个3字节为一组的数据重新编码成了4个字节。当所要编码的数据的字节数不是3的整倍数，也就是说在分组时最后一组不够3个字节。这时在最后一组填充1到2个0字节。并在最后编码完成后在结尾添加1到2个 “=”。

例：将对ABC进行BASE64编码：

1、首先取ABC对应的ASCII码值。A（65）B（66）C（67）；
2、再取二进制值A（01000001）B（01000010）C（01000011）；
3、然后把这三个字节的二进制码接起来（010000010100001001000011）；
4、再以6位为单位分成4个数据块,并在最高位填充两个0后形成4个字节的编码后的值，（00010000）（00010100）（00001001）（00000011），其中蓝色部分为真实数据；
5、再把这四个字节数据转化成10进制数得（16）（20）（9）（3）；
6、最后根据BASE64给出的64个基本字符表，查出对应的ASCII码字符（Q）（U）（J）（D），这里的值实际就是数据在字符表中的索引。

注：BASE64字符表：ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/

二、解码规则
解码过程就是把4个字节再还原成3个字节再根据不同的数据形式把字节数组重新整理成数据。

三、C#中的实现

private string Encode64(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;
    int page = messageLen / 3;
    int use = 0;
    if ((use = messageLen % 3) > 0)
    {
        for (int i = 0; i < 3 - use; i++)
            byteMessage.Add(empty);
        page++;
    }
    outmessage = new System.Text.StringBuilder(page * 4);
    for (int i = 0; i < page; i++)
    {
        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];
        int[] outstr = new int[4];
        outstr[0] = instr[0] >> 2;
        outstr[1] = ((instr[0] & 0x03) << 4) ^ (instr[1] >> 4);
        if (!instr[1].Equals(empty))
            outstr[2] = ((instr[1] & 0x0f) << 2) ^ (instr[2] >> 6);
        else
            outstr[2] = 64;
        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();
}

private string Decode64(string 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);
}

四、Delphi中的实现

注：需引用“ StrUtils”

//定义码表
const
BaseTable: string = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/';

//编码程序
function Encode64(const test:string): string;
var
s, s1: string;
i, p, len, n, Addnum: integer;
begin
result := '';

S := '';
for i := 1 to length(test) do
    S := S + IntToHex(Ord(test[I]), 2);
//将字符串的十六进制数以字符串的形式表示出来
case (length(s) mod 3) of
    0: addnum := 0;
    1:
    begin
      s := s + '00';
      addnum := 2;
    end;
    2:
    begin
      s := s + '0';
      addnum := 1;
    end;
    else
      addnum := 0;
end;
len := length(s) div 3;
for i := 1 to len do
begin
    s1 := midstr(S, i*3-2,3);
    p := strtoint('$' + s1);
    n := p div 64;
    result := result + basetable[n+1];
    n := p mod 64;
    result := result + basetable[n+1];
end;
if addnum = 1 then
    result := result + '==';
if addnum = 2 then
    result[length(result)] := '=';
end;

//解码程序
function Decode64(const test:string): string;
var
s, s1, m:string;
i, len, t:integer;
begin
Result := '';
if length(test) = 0 then
    exit;
s := test;
for i := 0 to 1 do
    if s[length(s)] = '=' then
      setlength(s, length(s) - 1);
len := length(s) div 2;
for i := 1 to len do
begin
    s1 := midstr(s, i*2-1, 2);
    t := (Pos(s1[1], BaseTable) - 1) * 64 + (Pos(s1[2], BaseTable) - 1);
    m := m + inttohex(t, 3)
end;
if length(s) mod 2 = 1 then
begin
    t := (Pos(s[length(s)], BaseTable) - 1) * 64;
    m := m + inttohex(t, 3);
    setlength(m, length(m) - 2);
end;
len := length(m) div 2;
for i := 1 to len do
begin
    s := midstr(m, i * 2 - 1, 2);
    result := result + chr(strtoint('$' + s));
end;
end;

五、JavaScript中的实现

由于该函数是针对utf8编码的字符使用，所以调用时需进行utf8到utf16的相互转换，完整的网页调用例子如下 :

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3c.org/TR/1999/REC-html401-19991224/loose.dtd">

<HTML><HEAD><TITLE>Base64编码加密</TITLE>
<META http-equiv=Content-Type content="text/html; charset=gb2312">
<META content="MSHTML 6.00.3790.2817" name=GENERATOR></HEAD>
<BODY>
<TABLE cellSpacing=0 cellPadding=0 width=773 align=center border=0>
  <TBODY>
  <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(utf16to8(f.source.value))
    f.decode.value = utf8to16(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></TEXTAREA><BR><BR>Base64
      encode<BR><TEXTAREA name=output rows=4 cols=60></TEXTAREA><BR><BR>Base64
      decode<BR><TEXTAREA name=decode rows=4 cols=60></TEXTAREA><BR><BR><INPUT onclick=doit() type=button value=转换>
      </FORM></TD></TR></TBODY></TABLE></BODY></HTML>

Posted on 2006-12-29 21:56 Clark Zheng 阅读(2592) 评论(3) 编辑收藏举报

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