转自:http://www.cnblogs.com/yejianfei/archive/2013/04/06/3002838.html
base64是一种基于64个可打印字符来表示二进制数据的表示方法。由于26=64,所以每6位为一个单位,对应某个可打印字符。三个字节共24位,对应于4个base64单位,即3个字节需要用4个可打印字符来表示。它常用来作为电子邮件的传输编码。在base64中的可打印字符包括大写英文字母A-Z,小写英文字母a-z、阿拉伯数字0-9,这样共有62个字符,此外两个可打印符号在不同的系统中而不同,通常用加号(+)和正斜杠(/)。外加“补全符号”,通常用等号(=)。
完整的base64定义可见RFC 1421和RFC 2045。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RFC 822的规定,每76个字符,还需要加上回车符和换行符。可以估算编码后数据长度大约为原长的135.1%。
base64编码的时候,将三个自己的数据,先后放入一个24位的缓冲区中,先来的自己占高位。数据不足3个字节的话,在缓冲区中剩下的位用0补足。然后,每次取出6(因为26=64)位,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。
C语言源代码如下:
/** * base64编码、解码实现 * C语言源代码 * * 注意:请使用gcc编译 * * 叶剑飞 * * * * 使用说明: * 命令行参数说明:若有“-d”参数,则为base64解码,否则为base64编码。 * 若有“-o”参数,后接文件名,则输出到标准输出文件。 * 输入来自标准输入stdin,输出为标准输出stdout。可重定向输入输出流。 * * base64编码:输入任意二进制流,读取到文件读完了为止(键盘输入则遇到文件结尾符为止)。 * 输出纯文本的base64编码。 * * base64解码:输入纯文本的base64编码,读取到文件读完了为止(键盘输入则遇到文件结尾符为止)。 * 输出原来的二进制流。 * */ #include <stdio.h> #include <stdlib.h> #include <string.h> #include <unistd.h> #include <io.h> #include <fcntl.h> #include <stdbool.h> #ifndef MAX_PATH #define MAX_PATH 256 #endif const char * base64char = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"; char * base64_encode( const unsigned char * bindata, char * base64, int binlength ) { int i, j; unsigned char current; for ( i = 0, j = 0 ; i < binlength ; i += 3 ) { current = (bindata[i] >> 2) ; current &= (unsigned char)0x3F; base64[j++] = base64char[(int)current]; current = ( (unsigned char)(bindata[i] << 4 ) ) & ( (unsigned char)0x30 ) ; if ( i + 1 >= binlength ) { base64[j++] = base64char[(int)current]; base64[j++] = ‘=‘; base64[j++] = ‘=‘; break; } current |= ( (unsigned char)(bindata[i+1] >> 4) ) & ( (unsigned char) 0x0F ); base64[j++] = base64char[(int)current]; current = ( (unsigned char)(bindata[i+1] << 2) ) & ( (unsigned char)0x3C ) ; if ( i + 2 >= binlength ) { base64[j++] = base64char[(int)current]; base64[j++] = ‘=‘; break; } current |= ( (unsigned char)(bindata[i+2] >> 6) ) & ( (unsigned char) 0x03 ); base64[j++] = base64char[(int)current]; current = ( (unsigned char)bindata[i+2] ) & ( (unsigned char)0x3F ) ; base64[j++] = base64char[(int)current]; } base64[j] = ‘\0‘; return base64; } int base64_decode( const char * base64, unsigned char * bindata ) { int i, j; unsigned char k; unsigned char temp[4]; for ( i = 0, j = 0; base64[i] != ‘\0‘ ; i += 4 ) { memset( temp, 0xFF, sizeof(temp) ); for ( k = 0 ; k < 64 ; k ++ ) { if ( base64char[k] == base64[i] ) temp[0]= k; } for ( k = 0 ; k < 64 ; k ++ ) { if ( base64char[k] == base64[i+1] ) temp[1]= k; } for ( k = 0 ; k < 64 ; k ++ ) { if ( base64char[k] == base64[i+2] ) temp[2]= k; } for ( k = 0 ; k < 64 ; k ++ ) { if ( base64char[k] == base64[i+3] ) temp[3]= k; } bindata[j++] = ((unsigned char)(((unsigned char)(temp[0] << 2))&0xFC)) | ((unsigned char)((unsigned char)(temp[1]>>4)&0x03)); if ( base64[i+2] == ‘=‘ ) break; bindata[j++] = ((unsigned char)(((unsigned char)(temp[1] << 4))&0xF0)) | ((unsigned char)((unsigned char)(temp[2]>>2)&0x0F)); if ( base64[i+3] == ‘=‘ ) break; bindata[j++] = ((unsigned char)(((unsigned char)(temp[2] << 6))&0xF0)) | ((unsigned char)(temp[3]&0x3F)); } return j; } void encode(FILE * fp_in, FILE * fp_out) { unsigned char bindata[2050]; char base64[4096]; size_t bytes; while ( !feof( fp_in ) ) { bytes = fread( bindata, 1, 2049, fp_in ); base64_encode( bindata, base64, bytes ); fprintf( fp_out, "%s", base64 ); } } void decode(FILE * fp_in, FILE * fp_out) { int i; unsigned char bindata[2050]; char base64[4096]; size_t bytes; while ( !feof( fp_in ) ) { for ( i = 0 ; i < 2048 ; i ++ ) { base64[i] = fgetc(fp_in); if ( base64[i] == EOF ) break; else if ( base64[i] == ‘\n‘ || base64[i] == ‘\r‘ ) i --; } bytes = base64_decode( base64, bindata ); fwrite( bindata, bytes, 1, fp_out ); } } void help(const char * filepath) { fprintf( stderr, "Usage: %s [-d] [input_filename] [-o output_filepath]\n", filepath ); fprintf( stderr, "\t-d\tdecode data\n" ); fprintf( stderr, "\t-o\toutput filepath\n\n" ); } int main(int argc, char * argv[]) { FILE * fp_input = NULL; FILE * fp_output = NULL; bool isencode = true; bool needHelp = false; int opt = 0; char input_filename[MAX_PATH] = ""; char output_filename[MAX_PATH] = ""; opterr = 0; while ( (opt = getopt(argc, argv, "hdo:")) != -1 ) { switch(opt) { case ‘d‘: isencode = false; break; case ‘o‘: strncpy(output_filename, optarg, sizeof(output_filename)); output_filename[sizeof(output_filename)-1] = ‘\0‘; break; case ‘h‘: needHelp = true; break; default: fprintf(stderr, "%s: invalid option -- %c\n", argv[0], optopt); needHelp = true; break; } } if ( optind < argc ) { strncpy(input_filename, argv[optind], sizeof(input_filename)); input_filename[sizeof(input_filename)-1] = ‘\0‘; } if (needHelp) { help(argv[0]); return EXIT_FAILURE; } if ( !strcmp(input_filename, "") ) { fp_input = stdin; if (isencode) _setmode( _fileno(stdin), _O_BINARY ); } else { if (isencode) fp_input = fopen(input_filename, "rb"); else fp_input = fopen(input_filename, "r"); } if ( fp_input == NULL ) { fprintf(stderr, "Input file open error\n"); return EXIT_FAILURE; } if ( !strcmp(output_filename, "") ) { fp_output = stdout; if (!isencode) _setmode( _fileno(stdout), _O_BINARY ); } else { if (isencode) fp_output = fopen(output_filename, "w"); else fp_output = fopen(output_filename, "wb"); } if ( fp_output == NULL ) { fclose(fp_input); fp_input = NULL; fprintf(stderr, "Output file open error\n"); return EXIT_FAILURE; } if (isencode) encode(fp_input, fp_output); else decode(fp_input, fp_output); fclose(fp_input); fclose(fp_output); fp_input = fp_output = NULL; return EXIT_SUCCESS; }
时间: 2024-10-05 05:05:07