Abstract: The public ledger of Bitcoin blockchain system offers ownership proof for distributed users by revealing all transaction details from coinbase transaction to unspent transaction output. However, an adversary could deanonymize user identities by transaction graph analysis and obtain transaction amount which reveals users’ privacy. This paper resolves this problem and uses both mixing and confidential transaction technique to achieve a full anonymous blockchain system by a one-way aggregate signature scheme and a homomorphic encryption scheme. It protects user identities and transaction amount to achieve full anonymity. The one-way aggregate signature scheme compresses all individual signatures to an aggregated one without additional storage space, which could neutralize the storage overhead caused by confidential transaction to a certain extent. The homomorphic encryption scheme encrypts the plaintext transaction amount to the Pedersen-style ciphertext, which is validated without decryption. In addition, miners in our system would become entities for verifying, mixing and packing all transactions in blocks. Four-step validation mechanism is also designed to prevent transaction makers from cheating. Finally, we evaluate our system with related work from the aspect of privacy protection, in which our storage overhead is acceptable with full anonymity.

Key words: full anonymous blockchain, aggregate signature, identity privacy, confidential transaction, transaction amount privacy