ROT-13 is a simple way of encrypting a
document. Encryption
is the process if taking a document, translating it so that
in its encrypted form it is not readable, but can be decrypted
so that it returns back to its original readable form.
ROT-13 is the US government's idea of personal encryption.
Some powerful members of government wish that this was the
only form of encryption available to its citizens. Fortunately,
others have more realistic views.
Encrypting and decrypting ROT-13 is easy. It is short for
"Rotate 13 letters". If you know the alphabet (US centric, sorry, I realize)
then you can easily make a ROT-13 chart:
abcdefghijklm
nopqrstuvwxyz
Now say you want to decrypt the phrase "Uryyb jbeyq!". Take the
first letter, 'U'. It's on the second row of the handy chart, and it's the 22nd letter of the alphabet.
The letter right above 'U' is 'H', which is the 8th letter of the alphabet. 22 - 8 = 13, so turn the 'U' into an 'H' and move on to the next letter.
'r' coresponds with 'e' in the chart, and to doublecheck, 'r' is the 18th letter, and 'e' is the 5th, and 18 - 5 = 13.
This is a good way to scramble a message so that it takes longer to read, but it's not exactly cryptography.