Problem - Kevin Tafuro

strncat( buf, "mp", buf_len - strlen(buf));
break;
default:
strncat( buf, "/", buf_len);
}
}
buf[buf_len] = 0;
return buf;
}
int main(int argc, char *argv[ ]) {
char filename[32];
/* 0x01040603 is 03 . 06 . 04 . 01 -- note that the number is passed as little
* endian but read as big endian!
*/
printf("get_filename( ) returns \"%s\"\n",
get_filename(0x01040603, filename, sizeof(filename)));
return 0;
}
Strings can also be stored encrypted in the binary and in memory. You can achieve
this by generating separate object files with the encrypted strings in them, by
encrypting the strings in the binary after compilation, or by initializing the strings
with encrypted characters. The following code demonstrates the last technique,
using the A macro to subtract a constant value from each character in the string. Note
that this is not a strong encryption method, but rather a quick and simple obfuscation
of the value of each character.
#define A(c) (c) - 0x19
#define UNHIDE_STR(str) do { char *p = str; while (*p) *p++ += 0x19; } while (0)
#define HIDE_STR(str) do { char *p = str; while (*p) *p++ -= 0x19; } while (0)
Each character of the string must be initialized, which makes this method somewhat
cumbersome, but it allows the obfuscation to take place at compile time:
#include
int main(int argc, char *argv[ ]) {
char str[ ] = {
A('/'), A('e'), A('t'), A('c'), A('/'),
A('p'), A('a'), A('s'), A('s'), A('w'), A('d'), 0
};
UNHIDE_STR(str);
printf("%s\n", str);
HIDE_STR(str);
return 0;
}
680 | Chapter 12: Anti-Tampering
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