Thurs' Cyber Security Challenge Cipher (day 1 of 3)

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*Finally getting round to publishing this after writing it _months_ ago, others are in the pipeline half writen*

The first one of three ciphers was aimed at under 18's so should be a gentle ease into the world of cipher puzzling again.

We were presented with two wav files.

Listening to them we see that they're both Morse code, given that this is an "easy" cipher we can safely rule out any kind of stenography or hidden info and just take them at face value for the time being.

Now given these files total about 50 seconds of quite fast morse, we could spend ages listening to them trying to discern dot from dash from gap, and still be not too sure we got the text right (unless it's plain text right away, and where would the fun be in that?), we're going to have to aproach this from a techy stand point.

We could slow the waveform down a bit to give us a better chance of getting our dots and dashes, but as we're going to open it in an audio editor lets just look at the wave

The waveform in audacity, we can clearly see --. space .--. space -. space ...- space ..- space --.-

So looking at the two wavs we get:

Wav one:

Wav two:

Converting them to a more readable format:



Nothing instantly jumps out, but this was supposed to be an easy one yes? Easy cipher == Caesar shift. As per the last challenge we head to decoder and select "caesar bruteforce"

Wav one: Gibberish, nothing of note... maybe we're on the wrong lines.

Wav two: A HAH! ROT-23: ALPHAZETA that looks better. The chances of getting that by chance if it's not rot-23 are _very_ low

So we've got one lot of gibberish and one bit of sensible text, what can we do with them? Two bits of text to me says key and ciphertext, the simplest of keyed cipher is the Vigenere cipher, think of it as a series of caesar ciphers, where the amount of rotation for each letter is based off the key text.

Say we had a key of "abcd" and the plaintext "cipher" to encrypt we would shift c zero places (a becomes a), the i one place (a becomes b), p two places (a becomes c), h four places, e zero (we've run out of key so we start again) and the r one place. Our cipher would then be "cjrles", to decode we just do the same but rotating in the oposite direction.

The easy way of working this out is with a Vigenere square, a handy reference.

The easier way is to find an online Vigenere decoder and whack the cipher text and key into it.

Lo and behold


There we go "Sweetcorn", job done.

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