XOR only partially decrypts file

Question

I'm learning C, and it's going slowly because I'm teaching myself. I'm trying to create a small function that reads a file, XOR encrypts it byte by byte, and spits it back out. It seems to work for encryption, but when I decrypt only half of it is legible, the rest is gibberish.

int encrypt_file(void)
{
         //declare variables used
         FILE *src_file_ptr;
         FILE *dst_file_ptr;
         char infilename[96];
         char key[50];
         char outfilename[96];
         char temp_store[50];
         int plen;
 
         printf("Please enter the name of the file to encrypt: ");
         scanf("%s", infilename);
         printf("Please enter the name of the output file: ");
         scanf("%s", outfilename);
         printf("Please enter the key to encrypt the file: ");
         scanf("%s", key);
         plen = strlen(key);
         
         //test for existence of input file
         src_file_ptr = fopen(infilename, "r");
         if (src_file_ptr == NULL)
         {
                 printf("File does not exist!");
                 return 1;
         }       
         
         dst_file_ptr = fopen(outfilename, "a");
         //read and process file 50 bytes at a time
         while(fgets(temp_store, 50, src_file_ptr) != NULL)
         {
                 int i;
                 //XOR n bytes with key
                 for ( i = 0; i < strlen(temp_store); i++)
                 {
                         temp_store[i] = temp_store[i] ^ key[i%plen];
                         fprintf(dst_file_ptr,"%c",temp_store[i]);
                 }
 
         }
         fclose(dst_file_ptr);
         fclose(src_file_ptr);
         return 0;
 
}

int main(void)
{
   encrypt_file();
   return 0;
}

I've researched extensively here on stack overflow, and everything I've found is for XOR encrypting / decrypting set value strings. I'm trying to get it to work dynamically by reading in a file and asking for a password (key) from the user. Any help would be greatly appreciated.

Answer 1

So after much more painful head against the wall, and help from folks here I found the solution.

int encrypt_file(void)
   {
         //declare variables used
         FILE *src_file_ptr;
         FILE *dst_file_ptr;
         char infilename[96];
         char key[50];
         char outfilename[96];
         char temp_store[50];
         int plen;
 
         printf("Please enter the name of the input file: ");
         scanf("%s", infilename);
         printf("Please enter the name of the output file: ");
         scanf("%s", outfilename);
         printf("Please enter the key to perform encrypt / decrypt: ");
         scanf("%s", key);
         plen = strlen(key);
 
         //test for existence of input file
         src_file_ptr = fopen(infilename, "rb");
         if (src_file_ptr == NULL)
         {
                 printf("File does not exist!");
                 return 1;
         }
 
         dst_file_ptr = fopen(outfilename, "wb");
         //create and initialize iterator
         int i = 0;
         do
         {
                 //variable for new byte
                 char nb;
                 // check for end of file and exit if found
                 if (feof(src_file_ptr))
                         break;
                 //check where iterator is at. If same length as password, reset it.
                 if (i == plen)
                 {
                         i = 0;}
                 //read single character from file, in binary mode
                 char c = fgetc(src_file_ptr);
                 // combine file character with password character using XOR
                 nb = c ^ key[i];
                 //write new character to file as byte
                 fputc(nb, dst_file_ptr);
                 //increment to next letter in password
                 i++;
 
         } while(1);
         fclose(dst_file_ptr);
         fclose(src_file_ptr);
         return 0;
 }

int main(void)
{
encrypt_file();
return 0;
}

This works perfectly for text files, haven't tried binaries yet but all I needed was for plaintext so far.