Validation-free offchain transactions with unlinkable double spend detection

The so-called layer-two protocols are a class of blockchain scaling solutions. They allow to minimize onchain traffic, and therefore make state transitions (payments, for example) faster and more suitable for everyday use, while still preventing double spend attacks. Unfortunately, these solutions also have some downsides and tradeoffs (channel capacity, route availability, operator availability, etc.). In this work we study the possibility of simplifying and improving existing protocols for offchain transactions and describe a scheme that, without transaction validation, allows to detect a double spender and not trace other transactions. This scheme is based on the anonymous transferable e-cash system. We use an offchain analogue of the UTXO model, therefore there are offchain transactions for issue, transfer and redeem of a so-called note, containing a number that can be used as a secret key to make the corresponding token transfer transaction onchain.