Hi, /r/MegaLoungeAvapoet. I hid a picture from you!

This link was originally posted to /r/MegaLoungeAvapoet. See more things from Dan's Reddit account.

One of Reddits MegaLounges, access to which is gained by being gilded
 in the prior MegaLounge (or /r/lounge itself, in the case of the firs
t MegaLounge). For the last 5 years, its been possible to buy Reddit
 Gold subscriptions, and for most of that time its been possible to 
anonymously gift individual months of Reddit Gold to other users (know
n as gilding), in acknowledgement of a contribution theyve made on 
the site. Having Reddit Gold grants you access to the official gold 
subreddit /r/lounge; getting gilded while in /r/lounge gets you access
 to the unofficial /r/MegaLounge, and so on. There are several dozen 
levels. Im pretty sure that an outside observer, given the advance k
nowledge of this blog post, could easily tell when Im in the process 
of getting over an illness just by the food I eat. Im pretty sure tha
t I have a particular tell in the foods I look for when Im on the c
usp of recovering from a cold, like now: or, I suppose, on those rare 
ocassions that Ill have drunk enough to be suffering from a hangover.
 Take this lunchtime, for example. Ive been off work for the last cou
ple of days, laid low by what seems to be the very same cold that I wa
s sure Id dodged when everybody else got it, last month (I blame Anna
bel, the contagious little beast, whos particularly keen on shoving h
er hands into peoples mouths). Today Im back on my feet, but working
 from home: I skipped breakfast, but by lunchtime I felt able to face 
some food, and quickly determined what it was that I really wanted: An
 egg and cheese wafflestack. If you think it looks calorieladen and d
isgusting, then youre right: but you wouldnt be saying that if you w
ere recovering from an illness! Egg & Cheese Wafflestack Serves: 1 unw
ellbutrecovering person Preparation: 15 minutes Difficulty: if you c
ant make this, get the hell out of the kitchen Ingredients 4 frozen p
otato waffles. Im using Birds Eye ones, but honestly, who can tell th
e difference? ~ 30g mature cheddar cheese, grated or thinly sliced, br
ought to room temperature so it melts quickly 2 eggs A little vegetabl
e oil Tomato ketchup (alternatively, brown sauce works well) Method Gr
ill the waffles in accordance with the instructions. Meanwhile, fry th
e two eggs (sunny side up: keep the yolk fluid). Assemble in stacks,
 with each stack consisting of cheese sandwiched between two waffles, 
topped with an egg and the ketchup. Serve immediately. Eat as quickly 
as you dare. So now Im sitting here eating the taste of delicious rec
overy, generating 4096bit strong probable prime numbers (like you do)
, and reading the feedback on a browser plugin I released recently. An
d every part of that is a huge improvement upon lying ill in bed. I sp
ent last week in the French Alps with JTA, Ruth, Annabel, and some han
gerson. It was great to get out onto the snow again for some skiing a
s well as some skibased geocaching, but perhaps the most remarkable e
vents of the trip happened not on the pistes but on an afternoon off
 that I decided to take after a rather jarring 42km/h (26mph) faceplan
t earlier in the day. A great thing about taking a GPSr for snowsports
 is that you know exactly how fast you were going (my record is 101km/
h!) when you crash. Not to be deprived of the opportunity for some out
doors, though, I decided to spend the afternoon hiking out to villaflo
u, a geocache only about a kilometre and a half away from our chalet. 
Well: a kilometre and a half as the crow flies: it was also some dista

Geocaching Like Batman

As the days get longer and the weather gets better, woodland trails and city alleyways alike begin to more-frequently see a particular brand of explorer. Clutching GPS devices (or, increasingly, mid- to high-end mobile phones), these satellite-guided adventurers shy away from normal people, whom they call “muggles”. Outwardly, this is out of concern for the continuity of their tiny treasure, but as often as not, it’s because geocachers – and especially urban geocachers, who often don’t even have the excuse of “getting some fresh air” to justify their hobby – are likely to be seen as a little odd., “You do what for a hobby? Find lost lunchboxes?”

Geocache GC13WZQ, from a distance..
There’s a “hidden in plain sight” urban geocache in this picture. Can you spot it? (probably not, at this resolution)

I’ve written plenty about geocaching already, but the only important thing to know for this particular anecdote is how geocaches are rated to indicate how hard they are. There are two scales, each scored from one to five “stars”. The first scale is difficulty, which is about how challenging the geocache is to find – a 1-star rating means that it’s in plain sight, not camouflaged, etc., while higher ratings might mean that it’s well-concealed, tiny, disguised as something else, or requires that you solve a puzzle in order to determine where it is. The second scale is terrain, which is about how challenging the geocache is to get to. A 1-star rating is typically accessible by wheelchair – you certainly don’t need to leave paved roads and footpaths to get it; higher ratings might mean steep gradients, tree climbing, long hikes, and so on. The highest terrain ratings often mean that specialised skills or equipment are required (for example, rock climbing gear or a scuba tank).

Geocache GC13WZQ, zoomed-in
There it is: that capsule, magnetically-attached to the girder that supports the bridge, is the geocache.

As you can imagine, caches with a 5-star “terrain” rating are rarer, and are especially uncommon in built-up areas. Half-way up cliffs… deep inside caves… miles out to sea: these are the places you’d expect to see geocaches with the highest level of “terrain” score. So imagine my surprise when I discover GC13WZQ (“Swing Lower”), a geocache with a 1-star “difficulty” rating but a 5-star “terrain” rating, just a few minutes walk from Oxford City Centre. In the seven years this cache has been in place, it had seen fewer than 110 successful visitors: contrast to its neighbour, GCK57Z (“Swing Low”) – a virtual cache less than 10 metres away – which has seen about six times as many visits in only 3 years longer. This, I thought, was a cache I had to see.

The sides of the bridge, boarded up and with barbed wire. Photo by OxfordLad on Geocaching.com.
OxfordLad (who took this photo), and other geocachers claimed that, since early 2014, the cache was made entirely inaccessible by the boarding-up of the sides of the bridge.

Folks recently attempting to find the geocache had reported (OxfordLad, izybuzyfingers, twitcher50) that it had been made inaccessible by the recent addition of boards and barbed wire to the edges of the bridge. Counter-arguments were raised (sandvika, Mad H@ter) to show that this didn’t make the cache inaccessible; it merely made it accessible only by boat, which had already been suggested in the “attributes” for the cache.

Geocache with "boat" attribute
Only an idiot would attempt a ‘requires boat’ geocache without a boat. Right?

I’m not a believer in the idea that any particular geocache can only be found one particular way. Also: I don’t have a boat. So I decided to make an expedition to “Swing Lower” my own damn way. Approaching the bridge under which the cache is located, I immediately saw the boards and barbed wire that had been reported by those that had attempted it earlier in the year. But as I would soon discover, anybody who was put off by a little bit of plywood and the risk of damp feet really wasn’t built of the right stuff to be able to do what was required next. Put simply: boards and barbed wire are the least of your problems when you’re hunting for GC13WZQ.

Dan, braced between two I-beams about 5 feet apart, underneath a bridge.
It’s not the most conventional way to cross a bridge, I’ll admit.

The bigger challenge was getting to the cache once underneath the bridge. I discovered (perhaps with a little inspiration from “Jackhuber”) that it was possible to brace myself against a pair of the beams that run the length of the bridge and – facing down – shuffle sideways to get to the centre of the bridge. I felt acutely aware of the fact that until I got over the central channel, the depth of the water might not be enough to break my fall (especially if I slipped and fell head-first), but was reassured by the fact that I’d brought fellow ‘cacher and coworker kateevery and she was ready, perhaps not to swim out and get me but at least to call 999, should the need arise.

Dan holding the geocache he's found above his head, triumphantly.
This is how Freddie Mercury holds a geocache.

So there you go. To all of you wusses for whom “there are boards and barbed wire in the way” was an excuse: you hadn’t even begun to face the challenge of “Swing Lower”. I’ve written up a Batman-themed description of the expedition as part of my log report.

A screenshot of the clue for GC54F78, one of the caches in my new series.
Can you make out the coordinates in this image? No? Maybe it’d help if you looked at geo.danq.me.

This conveniently coincides with the week that I launched my new collection of puzzle geocaches, the Oxford Steganography Series – four geocaches (GC54F78, GC54F7B, GC54F7J, GC54F7N) whose coordinates are concealed within images or text, each of which contains a transparency film that can be used (I made a video showing how) to determine the coordinates of a fifth, bonus cache. I’m reasonably pleased with the series, and I’ve been enjoying reading the reports of the ‘cachers who’ve been out hunting for them, so far.

Geocache GC13WZQ, from a distance..× Geocache GC13WZQ, zoomed-in× The sides of the bridge, boarded up and with barbed wire. Photo by OxfordLad on Geocaching.com.× Geocache with "boat" attribute× Dan, braced between two I-beams about 5 feet apart, underneath a bridge.× Dan holding the geocache he's found above his head, triumphantly.× A screenshot of the clue for GC54F78, one of the caches in my new series.×

Executable Stenography… With A Difference

Somebody’s come up with a program that hides secret messages in executable programs. Well… that’s not so impressive – we’ve all hidden secret messages in JPEG files before by using programs to ‘flip’ certain pixels (example). This works by changing the image in subtle ways that the human eye won’t detect, but that the descrambling application will. But here’s the clever bit…

Typically, when encoding a ‘hidden message’ in an executable, one ‘pads’ the file, making it bigger. The technique used when encoding messages in graphics files can’t be used with executables, because ‘flipping’ bits of the file would stop the program from working (or at least, working as it should), which may arouse suspicion. But this new tool works by exploiting redundancy in the i386 instruction set, swapping instructions or blocks of instructions for other ones which are functionally identical. As a result, the original filesize remains the same, and the program maintains full functionality. It would take an eavesdropper to fully compare the executable with a known original executable in order to determine that there was even a message hidden within it, and (thanks to Blowfish cryptography) yet more effort to decode that message.