The Cairo Games – Vol. 1

Update, 02/23/2021: The Cairo Games Vol. 1 have ended! See the winners here.

See the solutions to the puzzles of the first round here.

Check out Vol. 2

Welcome to the first round of the Cairo Games – where you can test your coding skills by solving puzzles, competing against other coders. Winners get ETH, limited-edition NFTs, and infinite bragging rights.

How does the Competition Work?

On February 18th, at 4PM GMT StarkWare will publish a set of Cairo puzzles. In each puzzle you’ll be given a somewhat obfuscated Cairo program with some missing Prover Hints. You’ll have to understand what the program does, and add the missing Hints to make it run successfully.

The first to solve a puzzle will get a prize (which varies between 0.1 ETH and 1 ETH according to the puzzle’s level of difficulty). 

Each solver gets a limited edition NFT, minted exclusively for this round of the competition, and becomes a member of the Cairo Games Hall of Fame, published on the Cairo Games web page.

The Winners!

Congratulations to all the Cairo Games winners. You can see this list timestamped on Ropsten here

Puzzle Name	1st Place	2nd Place	3rd Place	Places 4-10
Bastet	Anon	Daniel Lubarov	AliKhambati	Alex Miao, Kadin Donohoe, wb, Tjaden Hess, Tomoya Nagasawa, iazid, Ka Chenot
Khepri	j	William Borgeaud
Anubis	William Borgeaud
Ptah	William Borgeaud	Ka Chenot
Anuket	Daniel Lubarov	William Borgeaud

The Puzzles!

Name	Difficulty	Prize	Hash	Solution
Bastet	Easy	0.1 ETH	0x01ccacb5473cbcc8032bf8804eca3fc6a68a6320afc7113ba2355862895e95e2	Here
Khepri	Easy	0.1 ETH	0x02bb25e03624218e0211798da4064586ea37958590167006bff1be82e0d99858	Here
Anubis	Medium	0.3 ETH	0x0005b19f277f97b73b8ac170fe57159274c2bbbfb65a213ecf55cd61508df973	Here
Ptah	Medium	0.3 ETH	0x0441921830d40b5be99e7a9108d43d9f50bfa3750dec33a23f70950f3c953166	Here
Anuket	Hard	1 ETH	0x001626f02c7ea1a6974ae3ab485216f148fe0255dd3132f862ef068b8c12a2bd	Here

All the puzzles will be live at exactly 4PM GMT, Feb 18th on the Cairo Playground

Why the hash?

Each puzzle has a unique program hash (this is the hash of the compiled code, excluding hints) that identifies it. When you register your solution on-chain, you need to supply the program hash.

Puzzle Example

To get you started, we prepared a puzzle example – a dry run – to make sure you understand how everything works. 

Go to the Cairo Playground, click on “The Cairo Games” and open the “Example” puzzle.

If you try to run it, it will fail saying Unknown value for memory cell. Indeed, the two local variables x and y are not initialized.
Let’s initialize them using a Hint:

Now the program runs successfully – which means you’ve solved the puzzle! 

It’s very important to understand that you’re allowed to add/change Hints, but you cannot add/change the Cairo code. In this example, removing the asserts is not a valid solution because it changes the code.

Submitting Your Solution to the Blockchain in 3 Steps

Step 1

Once you’ve found how to solve the puzzle, add a Hint that makes the program output your Ropsten Ethereum address (the competition runs using Ropsten Ethereum contracts). For example, if your address is 0x123456789a, write:

You can run it in the playground to verify that the output is indeed your Ethereum address (note that the output is shown as a decimal integer, To see the hexadecimal value, check the tooltip).

Step 2

Next, send your solution to the GPS, by clicking on “Send to GPS”. The GPS service will generate a proof for the validity of the run, and register it as a Fact on the blockchain (see here). This Fact functions as a stamp attesting to the fact you’ve solved the puzzle (without revealing your solution on-chain!).

Step 3

Now register your solution, by invoking the submitPuzzleSolution() method in the competition contract. The first solution to each puzzle will get a prize! (Once the list of puzzles is available, you’ll find there the prize for each puzzle).

Let’s review the arguments for submitPuzzleSolution():

a. rewardAddress: This is your Mainnet Ethereum address. If you want to get the prize or the puzzle NFTs, make sure you put here the correct address 🙂
b. submitterName: This is easy – your name. It will appear in the list of solvers even if you’re not the first to solve a puzzle.
c. programHash: This is the identifier of the puzzle you’ve solved. You’ll see this value in the Playground.

Note that the time of submitPuzzleSolution() will be used for the order of winners, not the time of sending the solution to the GPS.

How to Win?

Before the competition starts, we recommend that you:

1. Learn Cairo by following the two tutorials Hello, Cairo and How Cairo Works.
2. Install Metamask, or another wallet through which you can send Ropsten Ethereum transactions (for registering your solution).
3. Get some Ropsten ETH (using a Ropsten faucet). You can get it for free, and you just need enough for the gas cost of registration (0.01 ETH should be enough).
4. Solve the example puzzle in the Playground and register your solution to make sure everything runs smoothly.

And some more information:

1. If you’re looking for a fast implementation of the Pedersen hash function, don’t use the one in crypto/starkware/crypto/signature/signature.py – it’s meant as a reference.
   Check out the one here: crypto/starkware/crypto/signature/fast_pedersen_hash.py. It’s faster.
2. A few of the puzzles are of a mathematical nature. For those, it’s important to know that the field we’re working in is integers modulo 2^251 + 17*2^192 + 1. Also, some programs like Sage can be used for computations in the field (there are also online versions, such as https://sagecell.sagemath.org/).
3. You can find the code of the library functions (with some documentation) here.
4. You can install cairo locally to experiment, using: pip install cairo-lang. Afterwards, you can access cryptographic primitives using import starkware.crypto.signature and cairo compiler internals using import starkware.cairo.lang.compiler.

The Playground has limited computational power, so if you need to, you can precompute things locally and merely write the result of the computation in a Hint.

Good luck!