Question

I am trying to get Base 64 encode value for a string value “simple” by using the implementation mentioned here

#include<openssl/sha.h>
#include<stdio.h>
#include<string.h>
#include<math.h>
#include<stdint.h>
#include<stdlib.h>


static char encoding_table[] = {'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H',
                                'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P',
                                'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X',
                                'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f',
                                'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n',
                                'o', 'p', 'q', 'r', 's', 't', 'u', 'v',
                                'w', 'x', 'y', 'z', '0', '1', '2', '3',
                                '4', '5', '6', '7', '8', '9', '+', '/'};

static int mod_table[] = {0,2,1};

char *base64_encode(const unsigned char *data,
                    size_t input_length,
                    size_t *output_length)
{
        printf("-- Begins -- ");
        *output_length = (size_t) (4.0 * ceil((double) input_length / 3.0));
        char *encoded_data = malloc(*output_length);

        for (int i = 0, j = 0; i < input_length;) {

        uint32_t octet_a = i < input_length ? data[i++] : 0;
        uint32_t octet_b = i < input_length ? data[i++] : 0;
        uint32_t octet_c = i < input_length ? data[i++] : 0;

        uint32_t triple = (octet_a << 0x10) + (octet_b << 0x08) + octet_c;

        encoded_data[j++] = encoding_table[(triple >> 3 * 6) & 0x3F];
        encoded_data[j++] = encoding_table[(triple >> 2 * 6) & 0x3F];
        encoded_data[j++] = encoding_table[(triple >> 1 * 6) & 0x3F];
        encoded_data[j++] = encoding_table[(triple >> 0 * 6) & 0x3F];
        }

    for (int i = 0; i < mod_table[input_length % 3]; i++)
        encoded_data[*output_length - 1 - i] = '=';
        printf(" -- Ends -- ");

    return encoded_data;


   }

int main(int argc, char **argv)
{
        unsigned char ibuf[] = "simple";
        size_t *outLen;
        size_t *inLen = (size_t) strlen(ibuf);
        char *encodeVal = base64_encode(ibuf, inLen, outLen);
        return(0);
}

When I tried debugging using gdb, all I got was:

Program received signal SIGSEGV, Segmentation fault.
0x000000000040073f in base64_encode (data=0x7fff65298a90 "simple", input_length=6, output_length=0x400a50) at openSha.c:25
25              *output_length = (size_t) (4.0 * ceil((double) input_length / 3.0));

What is the error here? I haven’t coded for a long time in C, so I am sorry if I am missing something obvious here.

Answer 1

 size_t *inLen = (size_t) strlen(ibuf);

This looks wrong.

inLen is a pointer to size_t but you are assigning it a size_t value.

Also this call:

base64_encode(ibuf, inLen, outLen);

base64_encode expects a size_t as its second argument but you are passing a size_t *.

And finally outLen is not initialized but you are passing its value to base64_encode.