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一. base64的编码规则 base64编码的思想是是采用64个基本的ascii码字符（并不是ascii码的从1-64码的数据，是从中选出的。）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：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（2011/03/14）
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。
public class base64manager<script type=text/网页特效> if ($ != jquery) { $ = jquery.noconflict(); } var islogined = false; var cb_blogid = 79235; var cb_entryid = 1983925; var cb_blogapp = "lcwws"; var cb_bloguserguid = "8c2e5b50-27ee-df11-ac81-842b2b196315"; var cb_entrycreateddate = "2011/3/14 16:25:00"; </script>
{
///
/// 编码
///
/// 要编码的字符串
///编码后的base64格式的字符串
public string encoder(string sstr)
{
#region 得到能被3整除的字节数组 byte[] bs = system.text.encoding.utf8.getbytes(sstr.tochararray());
if (bs.length % 3 == 0)
{
}
else if(bs.length%3==1)
{
bs = system.text.encoding.utf8.getbytes((sstr+"==").tochararray());
}
else if(bs.length%3==2)
{
bs = system.text.encoding.utf8.getbytes((sstr+"=").tochararray());
} #endregion #region 开始base64编码 byte[] bslast = new byte[bs.length / 3 * 4]; char[] c1;
char[] c2;
char[] c3;
char[] c4 = new char[8] { "0", "0", " ", " ", " ", " ", " ", " " };
char[] c5 = new char[8] { "0", "0", " ", " ", " ", " ", " ", " " };
char[] c6 = new char[8] { "0", "0", " ", " ", " ", " ", " ", " " };
char[] c7 = new char[8] { "0", "0", " ", " ", " ", " ", " ", " " };
char[] c8=new char[24];
for (int i = 0; i < bs.length; i = i + 3)
{
c1 = change(bs[i]);
c2 = change(bs[i + 1]);
c3 = change(bs[i + 2]);
for (int j = 0; j < 8; j++)
{
c8[j] = c1[j];
c8[j + 8] = c2[j];
c8[j + 16] = c3[j];
}
for (int k = 0; k < 6; k++)
{
c4[k + 2] = c8[k];
c5[k + 2] = c8[k + 6];
c6[k + 2] = c8[k + 12];
c7[k + 2] = c8[k + 18];
} bslast[i / 3 * 4 + 0] = (byte)change2to10(c4);
bslast[i / 3 * 4 + 1] = (byte)change2to10(c5);
bslast[i / 3 * 4 + 2] = (byte)change2to10(c6);
bslast[i / 3 * 4 + 3] = (byte)change2to10(c7);
} #endregion return changetobase64data(bslast);
} ///
/// 解码
///
/// 编码后的base64格式的数据
///解码后的数据
public string decoder(string sbase64data)
{
byte[] b = changetobytedata(sbase64data);
char[] c = new char[b.length / 4 * 3 * 8];
int istate = 0;
foreach (byte bb in b)
{
char[] cc = change(bb);
for (int i = 0; i < 6; i++)
{
c[istate++] = cc[i + 2];
}
} byte[] bl = new byte[b.length / 4 * 3];
int istateother = 0;
for (int i = 0; i < c.length / 8; i++)
{
char[] cs = new char[8] { " "," "," "," "," "," "," "," "};
for (int j = 0; j < 8; j++)
{
cs[j] = c[i * 8 + j];
}
bl[istateother++] = (byte)change2to10(cs);
} #region int icount = 0;
foreach (byte bbb in bl)
{
if (bbb == (byte)0)
{
icount++;
}
} byte[] bll = new byte[bl.length - icount];
for (int i = 0; i < bll.length; i++)
{
bll[i] = bl[i];
} #endregion
return system.text.encoding.utf8.getstring(bll);
} ///
/// 把变换完的字节数组转换为对应的base64表中的数据
///
/// 要转换的字节数组
///最终的编码之后的数据
private string changetobase64data(byte[] byt)
{
char[] sbase64table = "abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz0123456789+/".tochararray();
string sreturn = "";
foreach (byte b in byt)
{
sreturn += sbase64table[(int32)b];
}
return sreturn;
} ///
/// 编码后的数据转换为字节数组
///
/// 经过base64编码的数据
///编码后的字节数组
private byte[] changetobytedata(string sbase64data)
{
string sbase64table = "abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz0123456789+/";
char[] creturn = new char[sbase64data.length];
int istate = 0;
foreach (char c in sbase64data)
{
creturn[istate++] = (char)((sbase64table.indexof(c) == -1) ? system.text.encoding.utf8.getchars(new byte[] { ((byte)0) })[0] : sbase64table.indexof(c));
}
return system.text.encoding.utf8.getbytes(creturn);
} #region 十进制转二进制 <256的数据 ///
/// 十进制转为二进制数据（传入的数据只能为小于128的整数）
///
/// 十进制的数据
///转换成的二进制的数组
private char[] change(int i10)
{
bool state = false;
char[] ch = new char[] { "0", "0", "0", "0", "0", "0", "0", "0" };
int istate = 0;
while (i10 != 0)
{
istate++;
state = false;
if (i10 % 2 == 1)
{
i10 = i10 / 2;
state = true;
}
else
{
i10 = i10 / 2;
} if (state)
{
ch[8 - istate] = "1";
}
else
{
ch[8 - istate] = "0";
}
} return ch;
} ///
/// 把二进制的八位char数组转为十进制数据
///
/// 二进制数据
///十进制数
private int change2to10(char[] ch)
{
int ireturn = 0; for (int i = 0; i < 8; i++)
{
if (ch[i] == "1")
{
double d = double.parse((7 - i).tostring());
ireturn += (int32)system.math.pow(2.0, double.parse((7 - i).tostring()));
}
} return ireturn;
} #endregion
}