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simple encryption problem

Started by Damocles Jul 13, 2003 at 1:16 PM 4 replies 900+ views

Original Post

Jul 13, 2003 at 1:16 PM

I''m working on a simple encryption system for a shareware key setup.... Look at this code:

char convertName(int *mult, int num)
{
	int m=0;
	while (num>25)
	{
		num-=26;
		m++;
	}
	num+=(int)''A'';
	*mult=m;
	return (char)num;
}

It simply takes a character and returns another character in encrypted form. It first reduces it to the range of 0-25 and then adds ''A'' to it so that the resultant character sits between A and Z. I store mult so that I can store that as the multipler for decryption. The problem is, when it receives the character ''ü'' the resulting character returned is ''=''. If you look at your ascii table, you''ll see that ''='' is actually before ''A'' in the table, so how am I getting an equals sign int he output!? What have I missed here? I must be missing something (probably something simple) but I can''t see it for the life of me

btw - before anyone asks why I don''t just use divide and remainder operators, it''s because I''m going to expand it to a more complex system, assuming I can get this simple setup to work first

ApochPiQ

Jul 13, 2003 at 1:51 PM

Use this code instead:


char convertName(int *mult, unsigned char num)
{	
	int m=0;	
	while (num>25)	
	{		
		num-=26;		
		m++;
	}	
	num+=(unsigned char)''A'';	
	*mult=m;	
	return (char)num;
}

Converting from a char to an int can cause some very strange problems.

Damocles

Jul 13, 2003 at 2:19 PM

D''oh, I knew it would be something simple. I completely forgot that characters are 8 bits not 16.

At least it''s an easy fix, thanks.

Damocles

Jul 13, 2003 at 3:17 PM

That''s only the beginning of the encrypter. That''s not really enough to go on to break it. I''m just as paranoid as everyone else. Are you looking at me?

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