As I promised, here's a brief explanation of the reader challenge I posted earlier. (Deadlines in the summer? Baaad idea.) I will leave decoding as homework though.
Almost trivial ★☆☆☆☆
This is a simple substitution cipher using my haxor handle (repeated characters removed) as the key:
Reversal is almost trivial due to the distinct pattern it leaves in the letter frequency spectrum. "Almost", because there is an added challenge in the language used.
Shouldn't be very hard either ★☆☆☆☆
This message was transformed into audio with the Hellschreiber teleprinter. There's no further encryption. Some people noticed that there's a hint in the audio metadata; this was unintentional.
Might take some effort ★★★☆☆
A visual encryption scheme. A message is encoded in the difference of these two random dot patterns. I tried to add noise into the encoded message to make the resulting similarities in the patterns less obvious to the eye.
Okay, it's not really NSA-grade, that's why only four stars. But it's a Playfair cipher, using the following key:
$square = "WINDY". "ABCEF". "GHKLM". "OPQRS". "TUVXZ";
Whitespaces and punctuation was removed, and full stops were converted to "STOP".
I was surprised at how many people actually reversed this!