C語言base64編解碼

#include <stdio.h>
#include <string.h>


const char * base64char = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
const char padding_char = '=';

int base64_encode(const unsigned char * sourcedata, char * base64)
{
	int i=0, j=0;
	unsigned char trans_index=0;							// 索引是8位，但是高兩位都為0

	const int datalength = strlen((const char*)sourcedata);
    
	for (; i < datalength; i += 3) {	// 每三個一組，進行編碼  要編碼的數字的第一個
		
		trans_index = ((sourcedata[i] >> 2) & 0x3f);
		base64[j++] = base64char[(int)trans_index];

		// 第二個
		trans_index = ((sourcedata[i] << 4) & 0x30);

		if (i + 1 < datalength){
			trans_index |= ((sourcedata[i + 1] >> 4) & 0x0f);
			base64[j++] = base64char[(int)trans_index];
		}else{
			base64[j++] = base64char[(int)trans_index];
			base64[j++] = padding_char;
			base64[j++] = padding_char;
			break;								// 超出總長度，可以直接break
		}
		
		// 第三個
		trans_index = ((sourcedata[i + 1] << 2) & 0x3c);
		if (i + 2 < datalength) { 							// 有的話需要編碼2個
			trans_index |= ((sourcedata[i + 2] >> 6) & 0x03);
			base64[j++] = base64char[(int)trans_index];

			trans_index = sourcedata[i + 2] & 0x3f;
			base64[j++] = base64char[(int)trans_index];
		}else {
			base64[j++] = base64char[(int)trans_index];
			base64[j++] = padding_char;
			break;
		}
	}

	base64[j] = '\0'; 

	return 0;
}

int num_strchr(const char *str, char c)
{
	const char *pindex = strchr(str, c);
	
	if (NULL == pindex){
		return -1;
	}
	return pindex - str;
}

int base64_decode(const char * base64, unsigned char * dedata)
{
	int i = 0, j=0;
	int trans[4] = {0,0,0,0};

	for (;base64[i]!='\0';i+=4) { // 每四個一組，譯碼成三個字元

		trans[0] = num_strchr(base64char, base64[i]);
		trans[1] = num_strchr(base64char, base64[i+1]);
	
		dedata[j++] = ((trans[0] << 2) & 0xfc) | ((trans[1]>>4) & 0x03);

		if (base64[i+2] == '='){
			continue;
		}else{
			trans[2] = num_strchr(base64char, base64[i + 2]);
		}
	
		dedata[j++] = ((trans[1] << 4) & 0xf0) | ((trans[2] >> 2) & 0x0f);

		if (base64[i + 3] == '='){
			continue;
		}else{
			trans[3] = num_strchr(base64char, base64[i + 3]);
		}
		
		dedata[j++] = ((trans[2] << 6) & 0xc0) | (trans[3] & 0x3f);
	}

	dedata[j] = '\0';

	return 0;
}


int main()
{
    const unsigned char str[] = "admin:abcd1234789";
    const unsigned char *sourcedata = str ;
    char base64[128];

    base64_encode(sourcedata, base64);

    printf("編碼：%s\n",base64);

    char dedata[128];

    base64_decode(base64, (unsigned char*)dedata);

    printf("譯碼：%s\n", dedata);

    return 0;
}