CaptureCanton is a collection of "capture the funds" exercises for devs and security researchers in the Canton ecosystem — think Damn Vulnerable DeFi, but for Daml/Canton.

Canton's model is different from a public EVM chain: workflows are private, authorization is explicit (signatory / observer / controller), and state transitions are enforced by the ledger rather than by contract bytecode alone. So instead of reentrancy and flash loans, these challenges are about finding the gap in a contract's authorization logic or data model — a party that can act when it shouldn't, a check that's missing, a state that can drift out of sync with reality.

Each challenge gives you a deliberately flawed Daml contract and a role to exploit it from. Your job: steal the funds anyway.

⚠️ Not production code. Every contract in this repo is intentionally broken and exists purely to be exploited for learning. Don't copy these patterns into real projects, and don't treat any contract here as a reference implementation of "correct" Daml — assume it has bugs, because it does.

You need the Daml SDK installed locally.

# macOS / Linux
curl -sSL https://get.daml.com/ | sh

# then make sure ~/.daml/bin is on your PATH, and verify:
daml version

For Windows or other install options, see the official Daml installation docs.

Each challenge pins its own SDK version in daml.yaml (currently 3.4.11). You don't need to match it manually — the daml assistant will fetch and use the right version automatically the first time you build a project that requests it.

CaptureCanton/
├── 1-TheBeginning/        Challenge 1
├── 2-VaultItIs/            Challenge 2
├── common/                 Shared Daml packages used by some challenges
└── README.md               You are here

Every challenge folder has the same shape:

N-ChallengeName/
├── README.md               The brief: your role, your goal
├── main/
│   └── daml/*.daml          The flawed contract — this is what you're attacking
├── test/
│   └── daml/*Test.daml      Where you write your exploit, as a Daml Script
└── multi-package.yaml        Wires main + test together for the IDE/build tooling

• main/ is the "deployed" contract. Treat it as read-only — you're not meant to edit it, you're meant to find a way to abuse the choices/authorization it already exposes.

• test/ is your workspace. Each challenge's test file has a clearly marked block:

  -- ENTER SOLUTION BELOW --
  -> Enter HERE!
  -- ENTER SOLUTION ABOVE --

  Write your exploit only inside that block. Everything else in the test file is scaffolding (party setup, the initial contract state, the final assertion that checks whether you actually pulled it off) — leave it as-is.

1. cd into the challenge folder, e.g. cd 2-VaultItIs, and read its README.md for the specific scenario and goal.

2. Open main/daml/*.daml and study the contract: who are the signatories/observers, what choices exist, who can controller each one, what does each choice actually check before acting?

3. main and test are separate Daml packages — test depends on a built .dar of main (see test/daml.yaml's data-dependencies), so build main first:

   cd main
   daml build

4. Write your exploit inside the marked block in test/daml/*Test.daml, then run it:

   cd ../test
   daml test

   daml test runs the Daml Script and checks the final assertion — if it passes, the assertion's condition (e.g. you drained the vault) held true and you've solved the challenge.

5. Prefer an interactive view? Run daml studio from the challenge's test/ folder to open VS Code with inline Script Views, so you can watch contract state change as your exploit executes step by step.

• These bugs live in authorization design, not cryptography or reentrancy. Ask: does every controller actually deserve the power a choice gives them? Does an ensure or assert check what it looks like it checks? Can a party reach a choice they were only meant to observe?
• The contracts intentionally have no explanatory comments — the challenge is reading and reasoning about Daml authorization semantics yourself, not pattern-matching a comment. Using AI to skip that step means you skip the point of the exercise.
• If daml test fails with a missing-.dar error, you skipped step 3 above (or changed main and need to rebuild it).

Good luck!