Convert uint8_t array (Hexadecimal) to string in C - c

Question

Requirements
I'm a developer but with near-zero experience with C until a week ago. For a project, I need to encrypt/decrypt source-code/text files and need to use C for that.
What I did till now?
I'm using Kokke/tony-AES-c library for it and implementing it with pkcs7 padding as explained in this Gist.
In my code (given below), I have a function my_encrypt, which is encrypting contents and returning uint8_t array (which contains hex). I need to save it and read it later from a file for decryption. I know how to save a string into a file but how can I save uint8_t in a file.
For this, I need to convert uint8_t to string but after trying multiple solution, I am unable to do it.
Question
How can I convert uint8_t array (which contains hex) to string in C.
My code
#include <stdio.h>
#include <string.h>
#include <stdint.h>
#include <errno.h>
#include <stdlib.h>
#define CBC 1
#define DECRYPT 0;
#define ENCRYPT 1;
#include "aes.h"
#include "pkcs7_padding.h"
const uint8_t * my_encrypt(char *report) {
//Initialization Vector
uint8_t iv[] = { 0x75, 0x52, 0x5f, 0x69, 0x6e, 0x74, 0x65, 0x72, 0x65, 0x73, 0x74, 0x69, 0x6e, 0x67, 0x21, 0x21 };
uint8_t i;
// char* report = "my super secret thing that needs to remain that way!";
char* key = "thisIstheKey";
int dlen = strlen(report);
int klen = strlen(key);
printf("THE PLAIN TEXT STRING = ");
for (i=0; i<dlen;i++){
printf("%c", report[i]);
}
printf("\n");
//Proper Length of report
int dlenu = dlen;
if (dlen % 16) {
dlenu += 16 - (dlen % 16);
printf("The original length of the STRING = %d and the length of the padded STRING = %d\n", dlen, dlenu);
}
//Proper length of key
int klenu = klen;
if (klen % 16) {
klenu += 16 - (klen % 16);
printf("The original length of the KEY = %d and the length of the padded KEY = %d\n", klen, klenu);
}
// Make the uint8_t arrays
uint8_t hexarray[dlenu];
uint8_t kexarray[klenu];
// Initialize them with zeros
memset( hexarray, 0, dlenu );
memset( kexarray, 0, klenu );
// Fill the uint8_t arrays
for (int i=0;i<dlen;i++) {
hexarray[i] = (uint8_t)report[i];
}
for (int i=0;i<klen;i++) {
kexarray[i] = (uint8_t)key[i];
}
int reportPad = pkcs7_padding_pad_buffer( hexarray, dlen, sizeof(hexarray), 16 );
int keyPad = pkcs7_padding_pad_buffer( kexarray, klen, sizeof(kexarray), 16 );
printf("The padded STRING in hex is = ");
for (i=0; i<dlenu;i++){
printf("%02x",hexarray[i]);
}
printf("\n");
printf("The padded key in hex is = ");
for (i=0; i<klenu;i++){
printf("%02x",kexarray[i]);
}
printf("\n");
// In case you want to check if the padding is valid
int valid = pkcs7_padding_valid( hexarray, dlen, sizeof(hexarray), 16 );
int valid2 = pkcs7_padding_valid( kexarray, klen, sizeof(kexarray), 16 );
printf("Is the pkcs7 padding valid report = %d | key = %d\n", valid, valid2);
//start the encryption
struct AES_ctx ctx;
AES_init_ctx_iv(&ctx, kexarray, iv);
// encrypt
AES_CBC_encrypt_buffer(&ctx, hexarray, dlenu);
printf("the encrypted STRING = ");
for (i=0; i<dlenu;i++){
printf("%02x",hexarray[i]);
}
printf("\n");
return hexarray;
}
int main(int argc, char *argv[]) {
// File pointer
FILE *input_file;
int operation;
char * input_file_buffer = 0;
long input_file_length;
// ////////////////////////////////////////////////////////
// Read command line arguments
// ////////////////////////////////////////////////////////
// Make sure proper command params are supplied
if (argc != 3) {
printf("Usage: %s encrypt/decrypt filename\n", argv[0]);
return -1;
}
// Define operation type
if (strcmp(argv[1], "encrypt") == 0) {
operation = ENCRYPT;
} else if (strcmp(argv[1], "decrypt") == 0) {
operation = DECRYPT;
}
// ////////////////////////////////////////////////////////
// Open File contents
// ////////////////////////////////////////////////////////
// Open input_file to encrypt/decrypt.
input_file = fopen(argv[2], "rb");
if (!input_file) {
fprintf(stderr, "ERROR: '%s' file fopen error: %s\n", argv[2], strerror(errno));
return errno;
}
// Read contents of file in buffer
fseek(input_file, 0, SEEK_END);
input_file_length = ftell (input_file);
fseek(input_file, 0, SEEK_SET);
input_file_buffer = malloc (input_file_length);
if (input_file_buffer)
{
fread(input_file_buffer, 1, input_file_length, input_file);
}
// Close input_file
fclose(input_file);
// We have contents of file in input_file_buffer, let's print them.
printf("File contents:\n-------\n%s\n", input_file_buffer);
// Let's encrypt input_file_buffer
uint8_t result = 0;
result = my_encrypt(input_file_buffer);
// Convery result to string.
printf("main: Encrypted File contents:\n-------\n%d\n", result);
return 0;
}