According to CoinMeta, Wu said that Clara Shikhelman, Mikhail Komarov, and Aleksei Moskvin have proposed a meta-protocol called Shielded Bitcoin which enables private transactions on Bitcoin L1 without the need for a Bitcoin soft fork, a new blockchain, or a trusted operator. This solution hides the transaction amount, senders, recipients, and the specific notes spent by encrypting notes, nullifier, and zero-knowledge proofs. Any person can run indexer to verify transactions and prevent double-spending. However, it is not possible to control the observation of transaction times, notes amounts, transaction fees, and the Bitcoin transactions carrying data on the user's blockchain. The current solution only covers internal transfers within the privacy system; the mechanisms for entering and exiting the BTC will be described in subsequent papers based on the pipes approach.