How can I #include a file with encrypted string?

Question

I am writing a C app on Windows with MinGW/gcc. I need to use the #include directive to include a file that contains an encrypted string. The string will be decrypted at runtime. I want to do this so the string will not be visible if looking at the executable with a hex editor.

I tried this, but it doesn't work. You get the idea, though:

char *hidden_str =
#include "encrypted_text.dat"

There may be unescaped stuff in there that's confusing the compiler. I don't know. I don't know what happens to it after it's encrypted.

If there's a better approach to this, I'm open to it.

You would not use the preprocessor include directive in this case. — Doug, Jun 05 '11 at 00:45

score 4 · Accepted Answer · answered Jun 05 '11 at 01:01

If you installed and configured MSYS when you installed MinGW, you should have access to a command called xxd, which takes a hex dump of a file. By using the -i command line flag, you can get it to output a C-friendly file which you can easily import.

An example call would be:

xxd -i in_file output.h

The contents of output.h would then look like:

unsigned char in_file[] = {
  0x68, 0x65, 0x6c, 0x6c, 0x6f
};
unsigned int in_file_len = 5;

You can then include that file into your C source code and have access to it:

#include "output.h"

unsigned int i;
for(i = 0; i < in_file_len; i++)
{
    printf("%c", in_file[i]);
}

score 1 · Answer 2 · answered Jun 05 '11 at 00:55

1

The compiler doesn't like binary data in the file.

Try doing this instead:

char hidden_str[] = {
    65, 66, 67, ...
};

It's not that difficult to write a simple program to generate the relevant lines of data from the .dat file, with a limited number of characters per line.

answered Jun 05 '11 at 00:55

MRAB

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[xd](https://www.fourmilab.ch/xd/) and [xxd](http://man.cx/xxd) can generate those kinds of files. – icktoofay Jun 05 '11 at 00:56

score 1 · Answer 3 · answered Jun 05 '11 at 00:58

Encode it as hex/octal. I'm not sure what the simplest way would be to encode it -- you could use, eg, "\xAB\xCF...", the same with octal, or you could use an array initializer something like (don't quote me on this):

char hidden_str[64] = {0xAB, 0xCf, ...};

(You could even use decimal values for the initializer.)

Obviously, whatever you do you'll have to pre-process the encrypted text into a hex representation -- an easy job for a "toy" program.

How can I #include a file with encrypted string?

3 Answers3

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