function result = crypt(txt, seed, forward)
    if nargin < 3
	forward = true;
    end
    
    if forward
	sign = +1;
    else
	sign = -1;
    end

    rand('state', seed);
    loch = 33;
    hich = 126;
    range = hich+1-loch;
    rn = floor(range * rand(1, length(txt) ) );
    change = (txt >= loch) & (txt <= hich);
    result = txt;

    result(change) = loch + mod(result(change) + sign*rn(change) - loch, range);