Re: ITP seahorse

[Raul Miller <moth@debian.org>]

On Fri, May 19, 2000 at 03:22:19AM +0200, Simon Richter wrote:
> Are you sure about that? I remember something about programs providing
> the necessary hooks to insert encryption software to be restricted
> too.

I, too, have heard about this.  But I think it is something that people
have said, rather than something which makes sense.

Think about it: how many bits of encryption does a hook support?

If the hook supports, say, an 8 bit key, that means it's not a restricted
piece of munitions, right?  But if a hook supports, say, a 448 bit key,
that means it's a restricted piece of munitions, right?  But what about
a hook that doesn't care about keys?

Aside: it's possible to write a trivial routine which takes a
hash function and turns it into an encryption routine.  So imagine
I write a really dumb encryption routine, like:

#!/usr/bin/perl

sub hash {
	return @_;
}

# el-cheapo mechanism to turn string into a character generator
sub gen {
	my ($string)= @_;
	my $j= 0;
	return sub {
		return substr $string, $j++, 1;
	}
}

sub gen_encrypt {
	my ($key, $gen_next_char)= @_;
	my ($char, $new_byte);
	return sub {
		if (length ($char= &$gen_next_char)) {
			$key= hash $key;
			$new_byte= chr(ord($key) ^ ord($char));
			$key.= $new_byte;
			return $new_byte;
		} else {
			return undef;
		} 
	}
}       
	
sub gen_decrypt { 
	my ($key, $gen_next_char)= @_;
	my ($char, $new_byte);
	return sub {
		if (length ($char= &$gen_next_char)) {
			$key= hash $key;
			$new_byte= chr(ord($key) ^ ord($char));
			$key.= $char;
			return $new_byte;
		} else {
			return undef;
		}
	}
}


# demo
$stream= gen_decrypt "foo", gen_encrypt "foo", gen "bar\n";
while (defined ($c= &$stream)) {
	print $c;
}




Ok, nothing illegal about that.  Replace hash() with a 16 or 32 bit
checksum, and you're fine, regardless of the size of your key.  But,
replace hash with md5sum (use Digest::MD5 'md5'), and all of a sudden
you've got a 128 bit algorithm you can't export.  But that didn't make
the stupid xor encryption routine illegal.

-- 
Raul