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/***********************************************************************
===============
BASE64 Encoding
===============
Available on: http://freecode-freecode.blogspot.com/2008/02/base64c.html
Last access in: November, 10th 2009.
************************************************************************/
#include "stdio.h"
#include "stdlib.h"
#include "string.h"
#include "base64.h"
/**
* characters used for Base64 encoding
*/
const char *BASE64_CHARS = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
/**
* encode three bytes using base64 (RFC 3548)
*
* @param triple three bytes that should be encoded
* @param result buffer of four characters where the result is stored
*/
void _base64_encode_triple(unsigned char triple[3], char result[4])
{
int tripleValue, i;
tripleValue = triple[0];
tripleValue *= 256;
tripleValue += triple[1];
tripleValue *= 256;
tripleValue += triple[2];
for (i=0; i<4; i++)
{
result[3-i] = BASE64_CHARS[tripleValue%64];
tripleValue /= 64;
}
}
/**
* encode an array of bytes using Base64 (RFC 3548)
*
* @param source the source buffer
* @param sourcelen the length of the source buffer
* @param target the target buffer
* @param targetlen the length of the target buffer
* @return 1 on success, 0 otherwise
*/
int base64_encode(unsigned char *source, int sourcelen, char *target, int targetlen)
{
/* check if the result will fit in the target buffer */
if ((sourcelen+2)/3*4 > targetlen-1)
return 0;
/* encode all full triples */
while (sourcelen >= 3)
{
_base64_encode_triple(source, target);
sourcelen -= 3;
source += 3;
target += 4;
}
/* encode the last one or two characters */
if (sourcelen > 0)
{
unsigned char temp[3];
memset(temp, 0, sizeof(temp));
memcpy(temp, source, sourcelen);
_base64_encode_triple(temp, target);
target[3] = '=';
if (sourcelen == 1)
target[2] = '=';
target += 4;
}
/* terminate the string */
target[0] = 0;
return 1;
}
/**
* determine the value of a base64 encoding character
*
* @param base64char the character of which the value is searched
* @return the value in case of success (0-63), -1 on failure
*/
int _base64_char_value(char base64char)
{
if (base64char >= 'A' && base64char <= 'Z')
return base64char-'A';
if (base64char >= 'a' && base64char <= 'z')
return base64char-'a'+26;
if (base64char >= '0' && base64char <= '9')
return base64char-'0'+2*26;
if (base64char == '+')
return 2*26+10;
if (base64char == '/')
return 2*26+11;
return -1;
}
/**
* decode a 4 char base64 encoded byte triple
*
* @param quadruple the 4 characters that should be decoded
* @param result the decoded data
* @return lenth of the result (1, 2 or 3), 0 on failure
*/
int _base64_decode_triple(char quadruple[4], unsigned char *result)
{
int i, triple_value, bytes_to_decode = 3, only_equals_yet = 1;
int char_value[4];
for (i=0; i<4; i++)
char_value[i] = _base64_char_value(quadruple[i]);
/* check if the characters are valid */
for (i=3; i>=0; i--)
{
if (char_value[i]<0)
{
if (only_equals_yet && quadruple[i]=='=')
{
/* we will ignore this character anyway, make it something
* that does not break our calculations */
char_value[i]=0;
bytes_to_decode--;
continue;
}
return 0;
}
/* after we got a real character, no other '=' are allowed anymore */
only_equals_yet = 0;
}
/* if we got "====" as input, bytes_to_decode is -1 */
if (bytes_to_decode < 0)
bytes_to_decode = 0;
/* make one big value out of the partial values */
triple_value = char_value[0];
triple_value *= 64;
triple_value += char_value[1];
triple_value *= 64;
triple_value += char_value[2];
triple_value *= 64;
triple_value += char_value[3];
/* break the big value into bytes */
for (i=bytes_to_decode; i<3; i++)
triple_value /= 256;
for (i=bytes_to_decode-1; i>=0; i--)
{
result[i] = triple_value%256;
triple_value /= 256;
}
return bytes_to_decode;
}
/**
* decode base64 encoded data
*
* @param source the encoded data (zero terminated)
* @param target pointer to the target buffer
* @param targetlen length of the target buffer
* @return length of converted data on success, -1 otherwise
*/
int base64_decode(char *source, unsigned char *target, int targetlen)
{
char *src, *tmpptr;
char quadruple[4], tmpresult[3];
int i, tmplen = 3;
int converted = 0;
/* concatenate '===' to the source to handle unpadded base64 data */
src = (char *)malloc(strlen(source)+5);
if (src == NULL)
return -1;
strcpy(src, source);
strcat(src, "====");
tmpptr = src;
/* convert as long as we get a full result */
while (tmplen == 3)
{
/* get 4 characters to convert */
for (i=0; i<4; i++)
{
/* skip invalid characters - we won't reach the end */
while (*tmpptr != '=' && _base64_char_value(*tmpptr)<0)
tmpptr++;
quadruple[i] = *(tmpptr++);
}
/* convert the characters */
tmplen = _base64_decode_triple(quadruple, (unsigned char*)tmpresult);
/* check if the fit in the result buffer */
if (targetlen < tmplen)
{
free(src);
return -1;
}
/* put the partial result in the result buffer */
memcpy(target, tmpresult, tmplen);
target += tmplen;
targetlen -= tmplen;
converted += tmplen;
}
free(src);
return converted;
}
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