CRAC Demo

Demo app for the CRAC (Cross-Runtime Atomic Calls) feature of Tezos X: send a message from a Michelson wallet to an EVM smart contract via the CRAC gateway, then read it back.

Known issue: CRAC calls break block decoding

Successful CRAC calls currently break the EVM node's block decoding. See L2-958 for details.

A reproduction script is provided — see Reproducing the bug below.

Testnet

EVM RPC	https://demo.txpark.nomadic-labs.com/rpc
Tezos RPC	https://demo.txpark.nomadic-labs.com/rpc/tezlink
Blockscout	https://demo.txpark.nomadic-labs.com/
CRAC Gateway (Michelson)	KT18oDJJKXMKhfE1bSuAPGp92pYcwVDiqsPw
CRAC Gateway (EVM precompile)	0xff00000000000000000000000000000000000007
ERC-20 Wrapper	KT18oDJJKXMKhfE1bSuAPGp92pYcwVKvCChb

Bootstrap accounts

The testnet provides pre-funded accounts (no faucet). Documented in the TezosX Onboarding Guide.

EVM

Address	Private key
0x6ce4d79d4E77402e1ef3417Fdda433aA744C6e1c	0x9722f6cc9ff938e63f8ccb74c3daa6b45837e5c5e3835ac08c44c50ab5f39dc0
0xB53dc01974176E5dFf2298C5a94343c2585E3c54	0x3a6a6ca30c1ef1ce605a63a7a1a4ff4c689f8414ca0838bca29423f0ec280ff5
0x9b49c988b5817Be31DfB00F7a5a4671772dCce2B	0x0eb9bfa77d6cd145cdc0e3d6f902ee1464aeb5f62b02e38f111c9b60cd3adab5

Tezos (Michelson)

Account	Public key	Private key (seed)
bootstrap1	edpkuBknW28nW72KG6RoHtYW7p12T6GKc7nAbwYX5m8Wd9sDVC9yav	edsk3gUfUPyBSfrS9CCgmCiQsTCHGkviBDusMxDJstFtojtc1zcpsh
bootstrap2	edpktzNbDAUjUk697W7gYg2CRuBQjyPxbEg8dLccYYwKSKvkPvjtV9
bootstrap3	edpkuTXkJDGcFd5nh6VvMz8phXxU3Bi7h6hqgywNFi1vZTfQNnS1RV
bootstrap4	edpkuFrRoDSEbJYgxRtLx2ps82UdaYc1WwfS9sE11yhauZt5DgCHbU
bootstrap5	edpkv8EUUH68jmo3f7Um5PezmfGrRF24gnfLpH3sVNwJnV5bVCxL2n

Note: The commonly cited bootstrap1 key edsk3gUfUPyBSfrS9CCgmCIQsTCHGkviBDusMxDJstFtojtc1uo2KK7 contains an uppercase I which is invalid in base58. The correct key has a lowercase i (CiQ) and a different suffix (zcpsh).

Demo app workflow

1. Install

npm install

2. Compile the EVM contract

npm run compile

Compiles contracts/MessageStore.sol with solc and outputs contracts/MessageStore.json.

3. Deploy the EVM contract

npm run deploy -- <EVM_PRIVATE_KEY>

Example with a bootstrap account:

npm run deploy -- 0x9722f6cc9ff938e63f8ccb74c3daa6b45837e5c5e3835ac08c44c50ab5f39dc0

4. Configure

Create a .env file:

VITE_MESSAGE_STORE_ADDRESS=0x...deployed_address...

5. Run

npm run dev

Open http://localhost:5174.

6. Usage

1. Connect wallet — Click "Connect Michelson Wallet", approve in Temple
2. Send message — Type a message, click "Send" (calls the CRAC Gateway which routes to the EVM contract)
3. Read message — Click "Read" to fetch the stored message via eth_call

Note: Due to the bug described above, sending a message will currently fail with a deserialization error even though the CRAC call itself succeeds at the kernel level.

Reproducing the bug (L2-958)

The script scripts/reproduce-crac-bug.sh demonstrates that successful CRAC calls break the EVM node's block decoding, while reverted calls work fine.

Prerequisites

You need an octez-client built from the tezos repo. Standard releases don't know the testnet protocol (PtSeouLo...).

cd ~/git/tezos
eval $(opam env)
make octez-client

Run

# Default: looks for octez-client at ~/git/tezos/octez-client
./scripts/reproduce-crac-bug.sh

# Or specify the path:
OCTEZ_CLIENT=/path/to/octez-client ./scripts/reproduce-crac-bug.sh

What the script does

It sends 3 CRAC calls via octez-client to the gateway KT18oDJJKXMKhfE1bSuAPGp92pYcwVDiqsPw:

Test 1 — Default entrypoint (transfer 1 tez to an EVM address)

octez-client transfer 1 from bootstrap1 to KT18oDJJKXMKhfE1bSuAPGp92pYcwVDiqsPw \
  --arg '"0x6ce4d79d4E77402e1ef3417Fdda433aA744C6e1c"' --burn-cap 1

Result: operation is included in a block, but "Not enough data" deserialization error.

Test 2 — Call entrypoint (store a string on a payable EVM contract)

octez-client transfer 0 from bootstrap1 to KT18oDJJKXMKhfE1bSuAPGp92pYcwVDiqsPw \
  --entrypoint call \
  --arg 'Pair "0x3af5..." (Pair "store(string)" 0x<abi_encoded_hello>)' --burn-cap 1

Result: same "Not enough data" deserialization error.

Test 3 — Control: call with amount to a non-payable contract (reverts)

octez-client transfer 1 from bootstrap1 to KT18oDJJKXMKhfE1bSuAPGp92pYcwVDiqsPw \
  --entrypoint call \
  --arg 'Pair "0xd774..." (Pair "store(string)" 0x<abi_encoded_hello>)' --burn-cap 1

Result: receipt decoded correctly, shows "Cross-runtime call reverted".

Expected output

Test 1 & 2: "evm_node.dev.tezlink.deserialize_operation" / "Not enough data"
Test 3:     "Cross-runtime call reverted" (receipt decoded OK)

Root cause

Successful CRAC calls produce an internal operation in the receipt. The result tag for this internal operation (0x68) is not handled by SeouLo's operation_data_and_receipt_encoding, causing Data_encoding.Binary.of_bytes to fail with Not_enough_data.

Reverted calls do not produce internal operations, so the receipt is simpler and decodes fine. This is why test 3 works but tests 1 and 2 don't.

See the full analysis in L2-958.

CRAC format reference

The gateway %call entrypoint expects pair string (pair string bytes):

• string: EVM destination address (e.g. "0x3af5...")
• string: method signature (e.g. "store(string)")
• bytes: ABI-encoded parameters (without the 4-byte selector — the kernel computes it from the signature)

Source: enshrined_contracts.rs

Architecture

See ARCHITECTURE.md for technical design choices.