ROT13 hint decoder

What the hint is doing on the listing

Almost every cache listing carries a hint, and almost every hint is written with its letters moved thirteen places along the alphabet. It is the one piece of deliberate obscurity in the whole hobby, and it is not there to stop anybody.

The reason is ordinary. A listing is read before the walk, often at a kitchen table, and the eye takes in a page faster than the reader decides what to look at. A legible hint would be absorbed whether or not you wanted it, and the choice of whether to search unaided would be gone before you noticed you had made it. Shifting the letters puts one small, deliberate step between seeing the hint and using it.

That is the whole design. It is a courtesy extended to the finder, not a defence against one.

ROT13 is not encryption, and is not meant to be

Rotating the alphabet by thirteen is the weakest transformation that still stops casual reading. There is no key. The method is public and always the same. Anybody who wants the plain text can have it in seconds, from this page or a dozen others, or by hand on the back of the listing.

Which is the point worth taking away for anyone placing a cache: a hint is public writing. Nothing should go in one that would matter if a stranger read it. Not a landowner's name, not the combination to anything, and not a note to a particular finder. If it should not be read by the next passer-by, it does not belong in the hint field.

The convention also has a pleasing property that a stronger cipher would lose: it is its own undoing. Apply the same shift to encrypted text and you get the original back. That is why the box above needs no direction setting and no second button. One operation does both jobs, and pasting plain text in gives you the encrypted form to hand to somebody else.

Doing it in your head

The trick is a pairing rather than a calculation, and it takes about a minute to learn.

Write the alphabet in two rows of thirteen. A to M on the top, N to Z underneath, lined up so that A sits above N, B above O, and so on to M above Z. Every letter swaps with the one directly above or below it. A becomes N, N becomes A, and neither direction needs thinking about separately.

In practice you do not decode a whole hint. You decode the first two or three words, recognise the shape of it (under, behind, at the base of) and stop, because that is usually all the help you needed. Cachers who do this often stop needing any tool at all, which is the version that survives a damp listing and no signal.

A handful of letters become landmarks quickly. N is A. G is T. U is H. Those three alone unpick gur, which is the, and which begins a startling proportion of hints.

What the shift leaves alone

Only the twenty-six letters move. Digits, punctuation, accented characters and spaces pass through unchanged, which has two consequences worth knowing.

The first is that a hint containing a number shows it in plain view. An owner who writes three paces north of the post encrypts every word of it; one who writes 3 paces N hands you most of the meaning before you have decoded anything.

The second is that an encrypted hint gives away its own shape. Word lengths, punctuation and capitals survive the shift intact, so a short hint still looks short and a hint that is obviously two words is obviously two words. This is a reasonable objection to the whole convention and nobody has ever done anything about it, because the convention is not trying to be strong.

When it is worth decoding

There is no etiquette rule here. The hint is published for you and reading it is not cheating. What experienced cachers tend to do is hold it in reserve.

The common pattern is to search unaided for a set time, decode only if that runs out, and log honestly either way. A hint read after ten minutes of looking teaches you something about the hide; a hint read in the car teaches you nothing and removes the part you came for.

The exception is a cache you have already failed to find once. On a second visit the hint costs nothing and saves a repeat of the same twenty minutes, and there is no virtue in a second unsuccessful search of the same wall.

Occasionally a decoded hint turns out to be useless, you will know it when you see it is a real hint that real owners really write. That is worth a note in your log, kindly put. It is the only signal an owner gets that the hint field is not doing its job.