75th Anniversary Commemorative Coin | Australian Signals Directorate

On 1 September 2022, the Royal Australian Mint released a limited edition fifty cent commemorative coin to celebrate the Australian Signals Directorate's (ASD) 75th anniversary. Fifty thousand coins were produced for purchase by coin collectors and the Australian public, but have since sold out.

We would like to thank the Royal Australian Mint for collaborating with us and helping to celebrate 75 years of ASD.

In tribute to the importance of code breaking and evolution of signals intelligence, ASD experts collaborated with the Royal Australian Mint to design the coin’s unique cryptographic code. There were multiple layers of code on both sides of the coin, with a hidden message revealed after each layer was solved. We’ve provided more information about the history of the codes used on the coin and how to solve them below.

Accessible text version

Side B (Queens head)

ELIZABETH II - AUSTRALIA - 2022 - 50 CENTS

The following letters have a series of dots shown below them.

Using a 2 by 3 grid and numbered 1-2 (top row), 3-4 (middle row), 5-6 (bottom row).

B 1 2

T 1 3

H 1 2 3

A 1

S 1 4

A 1 2 4

Side A outer ring

.DVZIVZFWZXRLFHRMXLMXVKGZMWNVGRXFOLFHRMVCVXFGRLM.URMWXOZIRGBRM7DRWGSC5WVKGS

Side A inner ring

BGOAMVOEIATSIRLNGTTNEOGRERGXNTEAIFCECAIEOALEKFNR5LWEFCHDEEAEEE7NMDRXX5

Side A inner circle (two thirds of design)

1947-2022 - 75 - REVEAL AND PROTECT - AUSTRALIAN SIGNALS DIRECTORATE

Side A inner circle (one third of design)

E3B

8287D4

290F723381

4D7A47A291DC

0F71B2806D1A53B

311CC4B97A0E1CC2B9

3B31068593332F10C6A335

2F14D1B27A3514D6F7382F1A

D0B0322955D1B83D3801CDB2

287D05C0B82A311085A03329

1D85A3323855D6BC333119D

6FB7A3C11C4A72E3C17CCB

B33290C85B6343955CCBA3

B3A1CCBB62E341ACBF72

E3255CAA73F2F14D1B27A

341B85A3323855D6BB33

3055C4A53F3C55C7B22

E2A10C0B97A291DC0F

73E3413C3BE392819

D1F73B331185A33

23855CCBA2A3

206D6BE383

1108B

A brief history of code

Substitutions

Substitutions have formed the basis of ciphers for thousands of years.

They work by taking each component of the text (whether a letter or group of letters) and substituting it with some component of cipher text (which can be a letter, word, or symbol).

This means the original letters, words and sentences of the message become a jumble that is not recognisable unless you have the key to unlock the cipher text.

A particularly famous example is the Caesar cipher, where each letter in a message is shifted by a constant amount down the alphabet. For example, in a Caesar cipher with a shift of 3: A will be represented by D, B by E and so on through the alphabet with Z being represented as C.

A special Caesar cipher is known as ROT13. In this cipher, each letter is shifted 13 spots down the alphabet, which means that encryption and decryption are the same operation.

Atbash

Atbash is an ancient substitution cipher that was originally used to encrypt the Hebrew alphabet.

It is used in the Old Testament to obliquely refer to some proper nouns, and its name derives from the first, last, second, and second-last Hebrew letters (Aleph, Taw, Beth, Shin). It is easily transferable to any writing system where the components have a standardised order, like the Latin alphabet.

Unlike a Caesar cipher, Atbash maps each letter to its reverse, so A becomes Z, B becomes Y, C becomes X and so on.

Transpositions

Transpositions are an alternative to substitutions, where instead of changing the letter or word, its components are shuffled around in some way.

For example, writing a message across a ribbon that has been wrapped around a cylinder, then unrolling the ribbon. The message has now been scrambled, but can be deciphered by the recipient if they roll it around a cylinder of the same size.

More commonly, transpositions use fixed-length rows, with the cipher read off the columns in a set order. If done multiple times, and with sufficiently long messages, this can be very difficult to break by hand, and was used well into the 20th century.

Binary data using the Exclusive Or (XOR) operation

Binary data using the Exclusive Or (XOR) operation is a modern cipher scheme. The cipher uses binary’s 0s and 1s to perform logical operations that have an either or premise. A string of text can be encrypted by applying the XOR operator to every character using a given key. To decrypt the message, you need to reapply the XOR function with the same key.

If the key stream is generated randomly it is called a one-time pad. This is very hard to crack, as there is no way to recover the original text unless you have the correct key.

If the key stream is produced by a psuedo-random generator, it is known as a stream cipher. If the key stream is shorter than the message and sections of the key are repeated, or if different messages are encrypted with the same key, it substantially weakens the security of the system, and can lead to recovery of the original message.

How to solve the cryptographic code on ASD’s coin

Level One

The puzzle begins on the obverse side of the coin, which is the picture of the Queen’s profile. You will see 6 small braille markings used to represent the numbers 1 through to 6: ⠁ ⠃ ⠉ ⠙ ⠑ ⠋ centred under different letters. When laid out in numerical order, those letters spell ATBASH, which provides the clue for the type of cipher being used.

You will need to turn the coin over to solve the remaining layers of code.

Level Two

To begin level 2, start with the outer ring of 75 letters. You’ll see the surface of some letters has a slightly different surface to the others. This relates to a bonus layer and will be dealt with separately. The second layer of code can be found using the entire ring of letters.

Using the solution to level one (ATBASH), start at the ‘.’ marking and work your way clockwise around the circle. Remember, each Z represents an A, Y is B and so on. The encoded message reads:

.MWNVGRXFOLFHRMVCVXFGRLM·URMWXOZIRGBRM7DRWGSC5WVKGS·DVZIVZFWZXRLFHRMXLMXVKGZ

Which when deciphered looks like this:

.WEAREAUDACIOUSINCONCEPTANDMETICULOUSINEXECUTION·FINDCLARITYIN7WIDTHX5DEPTH

When you put in spaces and grammar, it says: "We are audacious in concept, and meticulous in execution. Find clarity in 7 width x 5 depth."

Level Three

Level 3 uses the inner ring of 70 letters on the coin’s reverse. This ring again has two puzzle components, with the textured letters part of a bonus level that will be dealt with separately.

Using the clue provided in level 2 (Find clarity in 7 width x 5 depth), you will see the letters are encoded using a transposition cipher that uses a 7x5 grid.

To decode the message, you will need to read the letters clockwise and write them down in 5 columns, starting a new column every 7 letters. You should get something that looks like this:

BGOAMVOEIATSIRLNGTTNEOGRERGXNTEAIFCECAIEOALEKFNR5LWEFCHDEEAEEE7NMDRXX5

B E L O N

G I N G T

O A G R E

A T T E A

M S T R I

V I N G F

O R E X C

E L L E N

C E W E M

A K E A D

I F F E R

E N C E X

O R H E X

A 5 D 7 5

To read the hidden message, write out the rows so they form a line of text, when you put in spaces and grammar says: "Belonging to a great team, striving for excellence, we make a difference. XOR hex A5D75."

You can also decode the message by writing it horizontally, starting a new row every 7 letters, and reading the message down the columns.

Level Four

The clue to solving level 4 is provided at the end of the level 3 solution. The letters XOR hex A5D75 let you know the next code uses binary data, and that A5D75 is the key for the encryption. The binary digits are found in the bottom right third of the coin’s main design area.

The characters only consist of the letters A-F and numbers 0-9. The block of letters begins with "E3B8287D …" and ends with "… 3831108B". This is the hardest level of the coin puzzle, and the most modern. Most people will need to use a computer to find the answer.

To decode the block of text, apply the XOR algorithm from each pair of hex characters, which represent one byte, to the corresponding key byte, where the key is 0xA5D75.

As an example, the first byte of the cipher is 'E3'. When you apply the XOR against 'A5', the first byte of the key, you get '46' which corresponds to 'F' in the standard ASCII alphabet. Applying the second byte of cipher text, 'B8’'against the second key 'D7' results in '6f' which gives you the letter 'o'.

This is what the XOR hex looks like:

E3B8287D4290F723 … ⊕

A5D75A5D75A5D75A … =

F o r 7 5 y e a …

When fully decoded with spaces and grammar included, the hidden message says: "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."

Bonus Levels!

You will have noticed different textures on some of the letters used to solve levels 2 and 3 of the coin challenge.

These form two bonus layers of code with additional messages from ASD.

Bonus level 1:

In the outer ring of letters, there are three finishes used. These represent a dot, a dash, and a space, which are used in Morse code.

When written down in order, the letters look like this:

MWNVGRXFOLFHRMVCVXFGRLM·URMWXOZIRGBRM7DRWGSC5WVKGS·DVZIVZFWZXRLFHRMXLMXVKGZ

But when you include the different finishes on each of the letters, the following Morse code is revealed:

-.. ... -... .- .-.. -... . .-. - .--. .- .-. -.- .---- ----. ....- --...

This “old technology” reveals the message: "DSB ALBERT PARK 1947"

This is the year and place of ASD’s birth, with the original name of DSB.

Bonus level 2:

The second bonus code is found on the inner ring of letters, where two finishes are used. They represent a 0 and a 1.

When you write down the finishes, they will display the following result:

Letters: BGOAMVOEIATSIRLNGTTNEOGRERGXNTEAIFCECAIEOALEKFNR5LWEFCHDEEAEEE7NMDRXX5

Markings: 1000001101001110001001000011110001011100100110010011000001100100110010

When decoded as binary with 7bits per byte, this reveals a ‘new tech’ bonus message: "ASD Cbr 2022"