Rainbow Bridge

Funds can be stolen if

1. incorrect checkpoint is submitted and nobody challenges it,
2. bridge administrator removes funds from the bridge escrow (CRITICAL),
3. destination token contract is maliciously upgraded (CRITICAL),
4. a contract receives a malicious code upgrade. There is no delay on code upgrades (CRITICAL).

Principle of operation

Rainbow is a Token Bridge that allows transferring assets and passing arbitrary messages between Ethereum, NEAR, and Aurora chains. During token transfers, Rainbow Bridge locks tokens in the escrow contracts on Ethereum and mints tokens on the Aurora or NEAR networks. When bridging back to Ethereum, tokens are burned on Aurora / NEAR and then released from the escrow on Ethereum.

Both inbound and outbound transfers are verified by the light client

Near Rainbow bridge implements a light client for both inbound and outbound transfers. For inbound transfers, checkpoints of NEAR state are submitted every 4 hours. These are optimistically assumed to be signed by 2/3 of Near Validators. The signatures are not immediately verified by Ethereum due to a different signature scheme used on NEAR and - as a result - very high gas cost on Ethereum. If signatures are found to be invalid, checkpoints can be permissionlessly challenged. Users can withdraw funds by submitting a Merkle proof of a burn event against the checkpoint. For outbound transfers, Ethereum light client is implemented on NEAR and a Merkle proof of a lock event must be presented.

• Funds can be stolen if incorrect checkpoint is submitted and nobody challenges it.

• Funds can be stolen if bridge administrator removes funds from the bridge escrow (CRITICAL).

Destination tokens are not verified

Tokens transferred end up as ERC20 tokens on AURORA or NEAR and they do not appear to be verified.

• Funds can be stolen if destination token contract is maliciously upgraded (CRITICAL).