Linux下base64加密（C实现）[转]

地址：http://hi.baidu.com/teng0210/blog/item/a61cfab5fe369b7b8ad4b228.html

来源chinaunix
源码稍有修改

//base64.h
#include
#include
#include
#include

extern char *base64_decode(const char*,char **);

extern char *base64_encode(const char*,char **);

//base64.c
#include "base64.h"

static char base64_table[255];

void base64_tableinit()

{

   int i,j;

   bzero(base64_table,255);

        for(j=0,i='A';i<='Z';i++) /*填base64编码表*/

                base64_table[i]=j++;

        for(i='a';i<='z';i++)

                base64_table[i]=j++;

        for(i='0';i<='9';i++)

                base64_table[i]=j++;

        base64_table['+']=j++;

        base64_table['/']=j++;

        base64_table['=']=j;

}

char *base64_decode(const char *cptr,char **rptr)

{

        char *res;

        int clen,len;

        static int init=0;

        if(cptr==NULL)

                return NULL;

        len=strlen(cptr);

        if(len%4) /*编了码的字符绝对是4的倍数*/

                return NULL;

        if(!init)

          {

                init=1;

                base64_tableinit();

          }

        clen=len/4;

        if((res=malloc(len-clen))==NULL)

                return NULL;

        for(*rptr=res;clen--;)

          {

                *res=base64_table[*cptr++]<<2&0xfc;         /*cptr后六位移动到最高位*/

                *res++|=base64_table[*cptr]>>4;               /*跟着下个字符低两位给res低两位*/

        *res=base64_table[*cptr++]<<4&0xf0;               /*填充res高四位其它清0*/

                *res++|=base64_table[*cptr]>>2&0x0f;    /*字符前六位移到低六位取低四位*/

                *res=base64_table[*cptr++]<<6;

                if(*cptr!='=')                                                 /*=号乎略*/

                   *res++|=base64_table[*cptr++];

          }

        return *rptr;

}

char *base64_encode(const char *cptr,char **rptr)

{

        char *res;

        int i,clen,len;

        len=strlen(cptr);

        clen=len/3;

        if(cptr==NULL||(res=malloc(clen+3*2+len))==NULL)

                  return NULL;

        for(*rptr=res;clen--;)

          {

                *res++=*cptr>>2&0x3f;          /*取ptr高6位放入res低6位*/

                *res=*cptr++<<4&0x30;          /*移动ptr最低2位到高6位然后清0其 它位*/

                *res++|=*cptr>>4;                  /*取ptr高4位给res低4位*/

                *res=(*cptr++&0x0f)<<2;        /*取ptr低4位移动到高6位*/

                *res++|=*cptr>>6;                  /*取ptr高2位给res低2位*/

                *res++=*cptr++&0x3f;

          }

        if(i=len%3)                                       /*处理多余字符只有两种情况多一个或者两个字符*/

          {

                if(i==1)                                    /*根据base64编码补=号*/

                  {

                        *res++=*cptr>>2&0x3f;

                        *res++=*cptr<<4&0x30;

                        *res++='=';

                        *res++='=';

                  }

                else

                  {

                        *res++=*cptr>>2&0x3f;

                        *res=*cptr++<<4&0x30;

                        *res++|=*cptr>>4;

                        *res++=(*cptr&0x0f)<<2;

                        *res++='=';

                  }

          }

        *res='=';                                               /*保证最后结位为=结束原因是因为base64里有为0的编码*/

        for(res=*rptr;*res!='=';res++)

       *res="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/="[*res];

        rptr[0][strlen(*rptr)-1]='\0';                 /*去掉最后一个=号*/

        return *rptr;

}

//main.c
#include "base64.h"

int main(void)
{
    char *src="abc";
    char *buf;
    base64_encode(src,&buf);
    printf("base64 encode:%s\n",buf);
    char *dec_buf;
    base64_decode(buf,&dec_buf);
    printf("base64 decode:%s\n",dec_buf);

    free(buf);
    free(dec_buf);
    return 0;
}