[math-fun] secret key cryptosystem?

From: Mike Stay <metaweta@gmail.com> To: math-fun <math-fun@mailman.xmission.com> Subject: Re: [math-fun] secret key cryptosystem? Pick some keyed nonlinear function of 64 bits to 64 bits, then do a 500-round Feistel cipher. It's pretty straightforward to get decent secret-key encryption; the tricky part is doing it quickly.

--now you are thinking more like I was thinking. (Albeit 64 bits seems small.) But, has anybody done that sort of thing and done it well? --Also, your other suggestion of ThreeFish is better than AES in the sense that this https://github.com/bmalkow/java-bc-threefish/tree/master/src says it implements it in only 390 lines. Albeit I'd like to get below 100 lines. (Also I want high portability.)