C＃实现Base64编码与解码及规则_生活百科

C＃实现Base64编码与解码及规则,博智网带你了解详细信息。
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#中的实现编码类：
/// <summary>/// Base64编码类。/// 将byte[]类型转换成Base64编码的string类型。/// </summary>public class Base64Encoder{byte[] source;int length, length2;int blockCount;int paddingCount;public static Base64Encoder Encoder = new Base64Encoder();public Base64Encoder(){}private void init(byte[] input){source = input;length = input.Length;if ((length % 3) == 0){paddingCount = 0;blockCount = length / 3;}else{paddingCount = 3 - (length % 3);blockCount = (length + paddingCount) / 3;}length2 = length + paddingCount;}public string GetEncoded(byte[] input){//初始化init(input);byte[] source2;source2 = new byte[length2];for (int x = 0; x < length2; x++){if (x < length){source2[x] = source[x];}else{source2[x] = 0;}}byte b1, b2, b3;byte temp, temp1, temp2, temp3, temp4;byte[] buffer = new byte[blockCount * 4];char[] result = new char[blockCount * 4];for (int x = 0; x < blockCount; x++){b1 = source2[x * 3];b2 = source2[x * 3 + 1];b3 = source2[x * 3 + 2];temp1 = (byte)((b1 & 252) >> 2);temp = (byte)((b1 & 3) << 4);temp2 = (byte)((b2 & 240) >> 4);temp2 += temp;temp = (byte)((b2 & 15) << 2);temp3 = (byte)((b3 & 192) >> 6);temp3 += temp;temp4 = (byte)(b3 & 63);buffer[x * 4] = temp1;buffer[x * 4 + 1] = temp2;buffer[x * 4 + 2] = temp3;buffer[x * 4 + 3] = temp4;}for (int x = 0; x < blockCount * 4; x++){result[x] = sixbit2char(buffer[x]);}switch (paddingCount){case 0: break;case 1: result[blockCount * 4 - 1] = '='; break;case 2: result[blockCount * 4 - 1] = '=';result[blockCount * 4 - 2] = '=';break;default: break;}return new string(result);}private char sixbit2char(byte b){char[] lookupTable = new char[64]{'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','+','/'};if ((b >= 0) && (b <= 63)){return lookupTable[(int)b];}else{return ' ';}}}
解码类：
///<summary>///Base64解码类///将Base64编码的string类型转换成byte[]类型///</summary>publicclassBase64Decoder{char[]source;intlength,length2,length3;intblockCount;intpaddingCount;publicstaticBase64DecoderDecoder=newBase64Decoder();publicBase64Decoder(){}privatevoidinit(char[]input){inttemp=0;source=input;length=input.Length;for(intx=0;x<2;x++){if(input[length-x-1]=='=')temp++;}paddingCount=temp;blockCount=length/4;length2=blockCount*3;}publicbyte[]GetDecoded(stringstrInput){//初始化init(strInput.ToCharArray());byte[]buffer=newbyte[length];byte[]buffer2=newbyte[length2];for(intx=0;x<length;x++){buffer[x]=char2sixbit(source[x]);}byteb,b1,b2,b3;bytetemp1,temp2,temp3,temp4;for(intx=0;x<blockCount;x++){temp1=buffer[x*4];temp2=buffer[x*4+1];temp3=buffer[x*4+2];temp4=buffer[x*4+3];b=(byte)(temp1<<2);b1=(byte)((temp2&48)>>4);b1+=b;b=(byte)((temp2&15)<<4);b2=(byte)((temp3&60)>>2);b2+=b;b=(byte)((temp3&3)<<6);b3=temp4;b3+=b;buffer2[x*3]=b1;buffer2[x*3+1]=b2;buffer2[x*3+2]=b3;}length3=length2-paddingCount;byte[]result=newbyte[length3];for(intx=0;x<length3;x++){result[x]=buffer2[x];}returnresult;}privatebytechar2sixbit(charc){char[]lookupTable=newchar[64]{'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','+','/'};if(c=='=')return0;else{for(intx=0;x<64;x++){if(lookupTable[x]==c)return(byte)x;}return0;}}}//解码类结束