[TriLUG] An Apple Puzzle

Fri May 1 21:19:20 EDT 2009

Argh - it is in Arizona or I would seriously love to go after this one. My first jobs in college were based on developing applications (mainly educational) for Apple and TRS-80 systems.

Since there have been so few finds, I don't want to work through to the answer and just give it away, but here are a few ideas to at least get you in the right direction. 

The first line, "call -151" drops you into the monitor where you enter in a series of opcodes at address 300, and then you jump into the code at address 300 to run it.

So the first question is how do you disassemble the hex codes into 6502 instructions?  The most obvious options include:
    * an apple emulator (you could simply copy/paste the text from the geocache page)
    * a 6502 disassembler
    * hand disassembly

Given that you don't expect to do any other 6502/Apple disassembly, it will probably be easiest to simply go the hand approach and convert each byte to a printable instruction.

Luckily the 6502 is a fairly easy to understand assembly language (long before RISC vs CISC arguments, when basically everything was RISC-ish in style). 

The 6502 only has 3 registers - an 8bit accumulator and two 16bit index registers X and Y. The cache description mentions there is an obvious error where an X/Y is wrong in one of the instructions. 

Let me know if you have any specific questions once you start, but I suspect the biggest 'hurdle' with this cache is that it requires a) someone who likes puzzles, b) a puzzler who is a programmer, and c) someone who wants to go through all the necessary steps to get to the answer. You already have the first two in your favor, so the third just requires the time to work through it.

Good luck, and please let us know if you get it.  It would be fun to create a Z80 cache similar in idea to that here... hmmm.. ;-)

-----Original Message-----
>From: Greg Brown <gwbrown1 at gmail.com>
>Sent: May 1, 2009 8:53 PM
>To: TMUG Discussion List <tmug-list at list.tmug.org>, "Internetworkers: http://www.ibiblio.org/internetworkers/" <internetworkers at lists.ibiblio.org>, Triangle Linux Users Group General Discussion <trilug at trilug.org>
>Subject: [TriLUG] An Apple Puzzle
>
>This is a Geocache puzzle and relates to old Apple II machines.  I don't
>know assembly language hence I wanted to ask you all.
>
>*Apple ][ Forever! GC1P5DQ*
>
>*N 33° 29.900 W 112° 00.250*
>
>A blast from the past.
>
>A very special puzzle cache. The coordinates listed are NOT the actual
>location of the cache. They will leave you about a block away from the
>actual cache location. Finding the cache requires access to an Apple ][ home
>computer system (one of the originals sold in the late 70's or early 80s)
>and a knowledge of 6502 Assembly language.
>
>NOTE: If you are an embedded systems designer with sufficient knowledge and
>experience with other 8-bit assembly languages, you may download data sheets
>for the 6502 and cross-reference the machine code by hand- in this case, no
>Apple ][ is necessary.
>
>Anyway, let's get down to business. Turn on your Apple and find your way to
>the Applesoft "]" prompt. Enter the following commands:
>
>CALL -151
300:A0 00 B9 11 03 F0 09 20 ED FD C8 E8 C8 4C 02 03
310:60 B3 B8
>B2 B3 B0 CA CE D3 D7 B2 B6 B5 B9 B9 B4
320:AE C0 B6 B9 B0 B9 B2 B1 B6 B4 B2
>B3 AC AE B9 B1
330:B1 B9 B1 B5 B4 B2 B2 D1 D7 C5 D3 B0 B1 B4 B0 B0
340:B8 AE
>AE B5 B1 B3 B4 B7 B6 B5 B3 B0 B9 AC B2 B3
350:C2 D3 C4 C1 D7 C5 C3 C2 D6 CB
>CC CC A0 B4 CE D0
360:C1 D2 C1 D5 D9 D4 C3 C6 C9 AC B9 CF 00 00 00 00
300G
>
>Gibberish, no? There is a minor bug in this program. Can you spot it? I will
>give you a hint: We have no need to use the "X" register for anything. One
>of the machine instructions needs to be replaced with the identical
>instruction that acts on the "Y" register instead.. so come on, all you
>Apple hax0rz out there, figure it out.
>
>Cache container: contains a logsheet and a pencil, and has room for a few
>more items. For those of you who have experience with these things, you will
>note that a special tool is often needed to open it. I have modified it to
>make it easy to open. Just lift the top straight up off the base, no
>twisting or bending needed. And, once again, apologies to anybody who came
>by today (3/26/09) and DNF. It took me a little longer than expected to
>secure this very unique cache container.
>
>Congratulations to Team AZFastFeet for the FTF!
>
>UPDATE 4/18/09: Raised difficulty from 4.5 back up to 5 stars due to such
>few attempts on this cache. Also added a couple of hints to help with the
>physical hunt on-site. With a ration of common sense and a properly-solved
>puzzle, you will not need to look at the encrypted hints.
>
>
>
> *Additional Hints (*
>*Encrypt*<http://www.geocaching.com/seek/cache_details.aspx?pf=&guid=038bed06-ed5c-473f-b585-46c72e8b23ee&decrypt=&log=&numlogs=>
>*)*
>
>
> No hints will be given for the puzzle itself. The puzzle accounts for 99%
>of what warrants this cache a 5-star difficulty. You will either know what
>to do, or you wont.
>
>Cache is not inside of any occupied structure, not in any shed, utility
>building, etc., and not inside of a vehicle. There is no reason to knock on
>any doors or trespass on neighbor muggles' private property. The message in
>the puzzle will tell you exactly where to look. The Coords may be off by
>5-10 feet, but that shouldn't matter.
>
>Cache is in a safe, well-lit area (day and night), accessible from the
>alley, and you will be out of sight of anybody (except for maybe the cache
>owner) while doing business at the cache.
>
>Despite these hints, the likelihood of finding the cache without solving the
>puzzle is still next to nil, so good luck!
>--
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