binary string => text string?

[mdoland]

I have a program that encrypts a password. I want to store the encrypted password in a text file. How do I do that? Is there some function I can use to automatically convert it to a text-based format and then back again when I need the binary? Base64 or what is best and whre do I get the functions from?

Language is C or maybe C++

I use Visual studio 2005

[drrngrvy]

You could just write to and read from the file in binary mode (set the std::ios::binary option when you open the file). Would that do?

[QuestionC]

The following code assumes that the encrypted password is stored as an array of 10 characters, whis more than likely isn't quite the same as what you are using. Otherwise, this should be sufficiently generic.

#include <stdio.h>
#include <assert.h>

#define PASS_SIZE 10

int main (void) {
   // The password is an arbitrary array of characters.
   unsigned char orig_pass[PASS_SIZE] = {176, 255, 0, 10, 73, 42, 5, 200, 0, 255};
   unsigned char restored_pass[PASS_SIZE];
   FILE * input, * output;
   int i;

   // Save the pass to a binary file.
   assert(output=fopen("passwd.key", "wb"));
   fwrite(orig_pass, PASS_SIZE, 1, output);
   fclose(output);

   // Read in the password from the binary file.
   assert(input=fopen("passwd.key", "rb"));
   fread(restored_pass, PASS_SIZE, 1, input);
   fclose(input);

   // Verify that the restored is equivalent to the original.
   for (i = 0; i < PASS_SIZE; ++i) {
      printf ("%d: %4u %4u\n", i, orig_pass[i], restored_pass[i]);
   }
   
   return 0;
}

[QuestionC]

Sorry, I didn't read the original question closely.

Here is a basic algorithm for converting between a binary array and a text array.

#include <stdio.h>
#include <assert.h>

// Convert a binary password to a text password.
// The output will take 2x bytes as the input.
bin2txt (size_t pass_size, unsigned char const * input, unsigned char * output) {
   int i;

   // For each element of the binary password, we're going to strip out the
   // lower and upper 4 bits, and make each a character.
   for (i = 0; i < pass_size; ++i) {
      unsigned char low_nibble;
      unsigned char high_nibble;

      low_nibble = input[i] & 0x0F;
      high_nibble = input[i] >> 4;

      output[i * 2] = low_nibble + 'A';
      output[i * 2 + 1] = high_nibble + 'A';
   }
}

// Convert a text password to a binary password.
// The output will take 1/2 bytes as the input.
txt2bin (size_t pass_size, unsigned char const * input, unsigned char * output) {
   int i;

   // Form each element of the binary password by merging two characters
   // from the input together.
   for (i = 0; i < pass_size; ++i) {
      unsigned char low_nibble;
      unsigned char high_nibble;

      low_nibble = input[i * 2] - 'A';
      high_nibble = input[i * 2 + 1] - 'A';

      output[i] = low_nibble | (high_nibble << 4);
   }
}

#define PASS_SIZE 10

int main (void) {
   // The password is an arbitrary array of characters.
   unsigned char orig_pass[PASS_SIZE] = {176, 255, 0, 10, 73, 42, 5, 30, 0, 255};
   unsigned char restored_pass[PASS_SIZE];
   char txt_version[PASS_SIZE * 2];
   int i;

   // Convert the pass to txt.
   bin2txt (PASS_SIZE, orig_pass, txt_version);

   printf ("Txt version:\n"); 
   for (i = 0; i < sizeof(txt_version); ++i)
      putchar(txt_version[i]);
   putchar('\n');
   putchar('\n');

   // Restore the pass from txt.
   txt2bin (PASS_SIZE, txt_version, restored_pass);

   printf ("Verification test.  Columns should be equal.\n");
   // Verify that the restored is equivalent to the original.
   for (i = 0; i < PASS_SIZE; ++i) {
      printf ("%d: %4u %4u\n", i, orig_pass[i], restored_pass[i]);
   }
   
   return 0;
}