[RC5] Temporary DES II cracking kludge for Macs

Barry Nathan barryn at pobox.com
Wed Jan 14 06:41:21 EST 1998


If you have Virtual PC and an extended keyboard, it's possible to run the
PC DES II (dual-core) client in the background, without using dozens of
megabytes of RAM (to be more specific, with VM turned on you'll need about
9.8MB of RAM once it's set up).

These instructions assume Win95 OSR2 (which is what comes with VPC if you
got the Win95 version). If you are using another OS on VPC, and a
dual-core client is available for it, you can probably figure out a
similar procedure. Similarly, it might be possible to set up a similar
procedure for SoftWindows or RealPC.

(1) Get the Win32 CLI dual-core client, and set it up ("rc5des -config").
As mentioned in another post on the RC5 mailing list, ABSOLUTELY !DO NOT!
use a block size of 2^32 (use something smaller). Also, do *not* import
any buffer files in from any previous v2.x RC5 clients (whether Mac or PC)
- - 2.7 changes the buffer format.

(2) Fetch a buffer file ("rc5des -fetch"). Make sure you are connected to
the Internet (through DUN or whatever) first.

(3) Get the DOS client and put its two .exe files (dos4gw.exe and
rc5desd.exe) in the Win32  client's directory.

(4) Shut down Win95, quit VPC, and reduce the memory allocation (both
preferred and max) to 10000K (VM on) or 10555K (VM off). In my experience,
increasing the memory allocation of VPC does *not* improve the client's

(5) Start VPC again, and when it says "Starting Windows 95" (before the
big Win95 splash screen), press F8.

(6) Choose "command line only" (I think it's option 6, but I'd rather not
stop the client to check b/c the DOS client doesn't shut down gracefully
and relies on the checkpoint file).

(7) Configure the DOS client ("dos4gw rc5desd -config"). Make sure there's
a DES checkpoint file. Also, try benchmarking the different CPU types
("dos4gw rc5desd -benchmark" or, for a shorter one, "dos4gw rc5desd
- -benchmark2") to see which optimizations run fastest - on my Mac, a
SuperMac C500 (180MHz PPC 603ev), the K5 client was fastest. Note that if
you don't do a "Restart Virtual PC" (Alt-Control-Delete isn't enough)
between benchmarks, it's possible for every benchmark after the first to
run at half speed. I've reproduced this with MacOS 7.6.1 w/o VM and w/VPC
1.0, but not with MacOS 8 w/VM and w/VPC 1.0.1.

(8) Get the client going ("dos4gw rc5desd"). If you are going to continue
using your Mac, hold down the Apple key (to enable the menu bar) and
switch to any other application. To get to your desktop in the Finder,
hide Virtual PC. Yes, VPC *will* continue running in the background - I've
double-checked this. However, it runs fastest in the foreground, so put it
into the foreground when you aren't using your Mac.

What kind of keyrate do I get? With a 180MHz PPC 603ev, MacOS 8, Speed
Doubler 8.0.1, and VM on, I get 92,000-94,000 keys/sec. Note that, when
VPC is in the background, DOS's software clock slows down along with the
dual-core client, so the keyrate measurement will be the same.

To suspend the client, you can save the PC environment when quitting VPC -
this is better than doing a Control-Break (Control-F15) on the client,
because it doesn't lose *any* work this way.

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