The ASD 50c Coin

On 1 September 2022, the Royal Australian Mint released a limited edition 50 cent commemorative coin to celebrate the Australian Signals Directorate’s (ASD) 75th anniversary.

One of the things that makes this coin so unique, is that it contains mulitple layers of cryptographic code.

Anyone who can crack the code and reveal the 4 hidden messages, is invited to submit the answers to the ASD.

Like most, you probably won’t be able to purchase a coin. Demand is high and they are only being produced in limited numbers. 
High resolution images are available on the ASD website but there is no need to manually type every character. An easier way is to simply click on the “Text Accessible” hyperlink to view all the text from the coin. 

There is a clue on the front of this coin, in the form of Braille. If you use this simple table, you will see that the dots can be interpreted as numbers.

Each number corresponds to a letter from the two words “ELIZABETH” and “AUSTRALIA”.

The result being:

ATBASH

Atbash is a monoalphabetic substitution cipher originally used to encrypt the Hebrew alphabet. It makes for a great clue and will now be used for the rest of this excercise.

URMWXOZIRGBRM7DRWGSC5WVKGS
DVZIVZFWZXRLFHRMXLMXVKGZMWNVGRXFOLFHRMVCVXFGRLM 

The first line of text is always going to be the most difficult to crack because we have no idea what encryption algorithm is required to decode it.

Fortunately, we have our first clue “atbash” and the internet. Using the CyberChef website, we can test almost any algorithm with a few clicks, very, very quickly. 

Using CyberChef, enter the text into the “input” field and type “atbash” into the search box.

The very first search result is “Atbash Cipher”, so let’s try that first. Drag the Atbash cipher into the “Recipe” column in the middle and watch the magic happen.

FINDCLARITYIN7WIDTHX5DEPTH
WEAREAUDACIOUSINCONCEPTANDMETICULOUSINEXECUTION

The clue to solve this answer comes from Answer 1.

FIND CLARITY IN 7 WIDTH X 5 DEPTH

This is a pretty strong clue and is telling us to write the text into at least one 7 x 5 grid. We have enough text here for two grids so the output on the left is the resulting answer:

BELONGINGTOAGREATTEAMSTRIVINGFOREXC ELLENCEWEMAKEADIFFERENCEXORHEXA5D75

This was the tricky one. Whilst there is enough information here to easily decrypt the puzzle programmatically, understanding what is required is far more technical.

Basically, the clue here is the ‘X OR Hex’. This tells us to use XOR Hexadecimal calculations to decrypt the block of text.

So the easiest way to solve this one is to just google “XOR Hex to Text” and you should find a few good sites, including this easy to use dcode.fr.

 Enter the large block of text (from the Side A inner circle) into the “TEXT TO BE XORED” field, select the “USE THE HEXADECIMAL KEY” radio button and enter “A5D75A5D75” into the text box before clicking “Decrypt”.

Note: The reason we need to type A5D75 twice is because 5 characters is not long enough to be a valid key to decrypt the XOR.

For 75 years the Australian Signals Directorate has brought together people with the skills, adaptability and imagination to operate in the slim area between the difficult and the impossible.

  This final bonus round involves the different shades of letters across the back of the coin.

If you count the shaded letters, the inner ring is binary and the outer ring is Morse.

Inner Ring

1000001101001110001001000011110001011100100110010011000001100100110010

ASDCbr2022

Outer Ring

The shading on each letter of the outer rim indicates either a 0, 1, or 2. Take note that the dots have markings when transcribing from the coin.

200001000021222201002221102212221022212012022102221212021012002120120210201

Shaded letters act as spaces, since they’re least common. Dark letters act as a dot, and light letters act as a dash.

.—- —-. ….- –… -.. … -… .- .-.. -… . .-. – .–. .- .-. -.-

1947DSBALBERTPARK

1947 is when the “Defence Signals Bureau (DSB)” was established, on Albert Park