  To strengthen the anonymity of Bitcoin, several centralized coin-mixing
providers (mixers) such as BitcoinFog.com, BitLaundry.com, and Blockchain.info
assist users to mix Bitcoins through CoinJoin transactions with multiple inputs
and multiple outputs to uncover the relationship between them. However, these
mixers know the output address of each user, such that they cannot provide true
anonymity. This paper proposes a centralized coin-mixing algorithm based on an
elliptic curve blind signature scheme (denoted as Blind-Mixing) that obstructs
mixers from linking an input address with an output address. Comparisons among
three blind signature based algorithms, Blind-Mixing, BlindCoin, and RSA
Coin-Mixing, are conducted. It is determined that BlindCoin may be deanonymized
because of its use of a public log. In RSA Coin-Mixing, a user's Bitcoins may
be falsely claimed by another. In addition, the blind signature scheme of
Blind-Mixing executes 10.5 times faster than that of RSA Coin-Mixing.
