Base64编码原理与应用

/**************************************************************************************************
Filename: base64.c
Revised: 2014-12-09 15.18 Description: this file use to descript the Base64 encode and decode
Author: huhao
Email: huhao0126@163.com
***************************************************************************************************/#include "stdlib.h"
#include "base64.h"static const char BASE_CODE[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";static const unsigned char base64_dec_map[128] =
{
127, 127, 127, 127, 127, 127, 127, 127, 127, 127, //0 ~ 9
127, 127, 127, 127, 127, 127, 127, 127, 127, 127, //10~19
127, 127, 127, 127, 127, 127, 127, 127, 127, 127, //20~29
127, 127, 127, 127, 127, 127, 127, 127, 127, 127, //30~39
127, 127, 127, 62, 127, 127, 127, 63, 52, 53, //40~49
54, 55, 56, 57, 58, 59, 60, 61, 127, 127, //50~59
127, 0xFF, 0, 0, 0, 0, 1, 2, 3, 4, //60~69
5, 6, 7, 8, 9, 10, 11, 12, 13, 14, //70~79
15, 16, 17, 18, 19, 20, 21, 22, 23, 24, //80~89
25, 127, 127, 127, 127, 127, 127, 26, 27, 28, //90~99
29, 30, 31, 32, 33, 34, 35, 36, 37, 38, //100~109
39, 40, 41, 42, 43, 44, 45, 46, 47, 48, //110~119
49, 50, 51, 127, 127, 127, 127, 127 //120~127
};/**************************************************************************************************
* @fn base64_encode
*
* @brief This function encode the bindata into base64 format.
*
* input parameters
*
* @param bindata - the input bindata
* @param output - the output base64 data.
* @param slen - the length of input data.
*
* output parameters
*
* None.
*
* @return the length of encoder output
**************************************************************************************************
*/
int Base64Encode(const unsigned char* bindata, unsigned char* output,int slen)
{
int vlen = 0;
unsigned char* temp_data; temp_data = bindata; while(slen > 0 )
{
*output++ = BASE_CODE[ (temp_data[0]>>2) & 0x3F ];
if(slen > 2 ) //长度大于三个字符 处理生成4个字符
{
*output++ = BASE_CODE[ ( ( temp_data[0] & 0x03 )<<4) | ( temp_data[1] >>4) ];
*output++ = BASE_CODE[ ( ( temp_data[1] & 0x0F )<<2) | ( temp_data[2] >>6) ];
*output++ = BASE_CODE[ ( temp_data[2] & 0x3F )];
}else if( slen == 2) //恰好为两个字符
{
*output++ = BASE_CODE[ ( ( temp_data[0] & 0x03 )<<4) | ( temp_data[1] >>4) ];
*output++ = BASE_CODE[ ( ( temp_data[1] & 0x0F )<<2)];
*output++ = '=';
}else if( slen == 1) //恰好为一个字符
{
*output++ = BASE_CODE[ (temp_data[0]&0x03) << 4];
*output++ = '=';
*output++ = '=';
} temp_data += 3;
slen -= 3;
vlen += 4;
}
*output = '\0'; //this is very improtant
return vlen;
}/**************************************************************************************************
* @fn GetCharIndex
*
* @brief This function get the mapping value.
*
* input parameters
*
* @param c - Base64 code
*
* output parameters
* none
* it has two ways to map from ciphertext to plaintext,one is lookup-table,and the other is value judgements.
* @return original value
**************************************************************************************************
*/
unsigned char GetCharIndex(unsigned char c)
{
#if 1
if( ( c >= 'A' ) && ( c <= 'Z'))
{
return c - 'A';
}else if( (c >= 'a') && (c <= 'z' ))
{
return c-'a'+26;
}else if( (c >= '0') && ( c <= '9'))
{
return c - '0' + 52;
}
else if( c == '+')
{
return 62;
}else if( c == '/')
{
return 63;
}else if(c == '=')
{
return 0xFF;
}
#else
return base64_dec_map[c];
#endif
return 0;
}/**************************************************************************************************
* @fn BaseDecode
*
* @brief This function decode the bindata into base64 format.
*
* input parameters
*
* @param input - the encoded input data
* @param output - the decode output data
* @param sLen - the length of encoded input data.
*
* output parameters
* none
*
* @return vlen - the length of decode data
**************************************************************************************************
*/
int Base64Decode(const unsigned char* input,unsigned char *output,int sLen)
{
static unsigned char lpCode[4] = {0};
unsigned char* data_temp = input;
int vlen = 0; //Base64 length must be a multiple of 4 including '='
if( sLen % 4 )
{
return -1;
} while(sLen > 0 )
{
lpCode[0] = GetCharIndex(data_temp[0]);
lpCode[1] = GetCharIndex(data_temp[1]);
lpCode[2] = GetCharIndex(data_temp[2]);
lpCode[3] = GetCharIndex(data_temp[3]); if( lpCode[3] == 0xFF )
{
if( lpCode[2] == 0xFF ) // if there has two '=' at the end
{
*output++ = (lpCode[0] << 2) | (lpCode[1] >>4);
vlen +=1;
break;
}else // if there has one '=' at the end
{
*output++ = (lpCode[0] << 2) | (lpCode[1] >>4);
*output++ = (lpCode[1] << 4) | (lpCode[2] >>2);
vlen +=2;
break;
}
}else
{
*output++ = (lpCode[0] << 2) | (lpCode[1] >>4);
*output++ = (lpCode[1] << 4) | (lpCode[2] >>2);
*output++ = (lpCode[2] << 6) | (lpCode[3]); data_temp+=4;
sLen -=4;
vlen +=3;
}
} *output = '\0'; //this is very improtant
return vlen;
}/*
main test function
*/
int test_base64()
{
unsigned char* output_buffer = NULL;
char input_str[100]={0}; int allocate_len;
int input_len;
int output_len; printf("Please input string : \n ");
scanf("%s",input_str); input_len = strlen(input_str);
printf("the length of input is %d \n",strlen(input_str)); //补齐字节数，使得输出缓存为4的倍数,这样来考虑，先把输入长度补齐到3的倍数，然后将其乘以4再除以3
allocate_len = ( input_len % 3 ) ? ( input_len + 3 - input_len%3 ) :( input_len);
allocate_len = ( allocate_len * 4 )/3; output_buffer = (unsigned char*)malloc(allocate_len+1); //加1 很重要，用于结束编解码的输出字符串
if(NULL == output_buffer)
{
printf("allocate memory fail! \n");
return -1;
}else
{
printf("success allocate %d bytes. \n",allocate_len);
memset(output_buffer,0,allocate_len);
} output_len = Base64Encode(input_str,output_buffer,input_len); printf("Base64ENcode(\" %s \" ,encoding output length is %d \") \n encode content is %s \" \n\n",input_str,output_len,output_buffer); memset(input_str,0,sizeof(input_str));
output_len = Base64Decode(output_buffer,input_str,output_len); printf("Base64Decode(\" %s \" ,decoding output length is %d \") \n decode content is %s \n",output_buffer,output_len,input_str); free(output_buffer); //release the allocated memory
output_buffer = NULL;
}