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.
Obtaining the coIN
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.
b=3 t=2 h=6 a=1 s=5 a=4
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 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.
AnswerS 1 and 2
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.
7 Width by 5 Depth
Typing out the third line into Excel is an easy way to visualise. You can also use the “Text to Columns” feature in Excel to help with this step.
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:
XOR Hex A5D75
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.
50c Shades of Grey
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.
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.
Shaded letters act as spaces, since they’re least common. Dark letters act as a dot, and light letters act as a dash.
.—- —-. ….- –… -.. … -… .- .-.. -… . .-. – .–. .- .-. -.-