Tech puzzles

• By considering clue 5 first, you can rule out numbers 3, 8, 5 and 7 from the other clues. 
• Clue 4 tells you the number 9 appears twice.
• Then use clue 1 to rule out numbers 2 and 0.
• Use clue 3 to determine the order of numbers 4 and second 9.
• This gives you the solution 1949 – the year ASIO was established.

To crack the code, assign each letter of the alphabet a number in order, e.g. A=1, B=2, C=3 etc. The breaks between numbers indicate a space between words. When you assign each letter a number, the code above reveals:

I like dogs

Apply the rules above and see if you can crack this code:

715154 162051814151514

To celebrate the Australian Signals Directorate’s 75^th birthday, we sent them an encoded message on Twitter. If you’re not sure what we said, or how we said it, find out how to decode our message below.

The coded message:

745a372233332742593831283d3d4415362b616566174c3c2433217
3585379372424365659302b2672275f50303761213654473c3132727
517452b2a353730435c3722613d26451536322f7c

The message is encoded using a repeating XOR (Exclusive OR) operation, with the key 75YEARS included as a hashtag and subtle hint. The XOR is a common bitwise operator used in computing, whereby two bits (0s and 1s) are compared – the result of the operation is 1 if the two bits are different (0 and 1) and 0 if the bits are the same (0 and 0, or 1 and 1). XOR-ing a message with a secret key scrambles the message.

How it works:

1. In order to XOR the above 76-character message with the key 75YEARS, we must equalise the length of both. This is done by repeating the key numerous times until we have a 76-character key:

Congratulations on 75 years of revealing their secrets & protecting our own.

75YEARS75YEARS75YEARS75YEARS75YEARS75YEARS75YEARS75YEARS75YEARS75YEARS75YEAR

2. We then perform the XOR operation on the unique ASCII code associated with the characters in two strings. This is most easily done using any kind of programming language by writing a short script, or using an online tool which can perform XOR on given input data. XOR can be done manually by converting both strings into binary and comparing them bit-by-bit to obtain the XOR result.

3. The XOR result, being in binary, is very long. We convert this to hexadecimal (base 16, commonly used in computing to represent binary data), resulting in the following encoded string.

74 5a 37 22 33 33 27 42 59 38 31 28 3d 3d 44 15 36 2b 61 65 66 17
4c 3c 24 33 21 73 58 53 79 37 24 24 36 56 59 30 2b 26 72 27 5f 50
30 37 61 21 36 54 47 3c 31 32 72 75 17 45 2b 2a 35 37 30 43 5c 37
22 61 3d 26 45 15 36 32 2f 7c

4. Due to the choice of key, each hexadecimal value contains two digits and as such can be compacted into a single numeric string without white space.

745a372233332742593831283d3d4415362b616566174c3c2433
2173585379372424365659302b2672275f50303761213654473c3
132727517452b2a353730435c3722613d26451536322f7c

Decoding:

Decoding of the hexadecimal string can be done by XOR-ing with the hexadecimal representation of the 76-character key above which when converted from ASCII to text will reveal the message, Congratulations on 75 years of revealing their secrets & protecting our own.

Notice there are some icons in the grid that are not listed in the key. When those icons are marked, the hidden message 'YOU' is revealed to solve the puzzle.