T-Mix: A Threshold Cryptography Mixing
Service for Bitcoin
Wafa F. Aldamegh and Laith A. Alsulaiman
Abstract
Bitcoin is the first successful implementation of the
blockchain, which eliminates the role of trusted centralized settlement entities. Although Bitcoin was designed
with anonymity in mind, it has recently faced privacy
challenges as some users’ identities have been revealed
(Biryukov and Khovratovich 2014; Fleder et al. 2015;
Maesa et al. 2016, 2017) To address this issue, mixing
services are used in Bitcoin to increase user anonymity.
Mixcoin provides a centralized mixing service that
reduces the impact of blockchain transaction analysis
by hiding the links among transaction addresses to
preserve users’ anonymity. However, Mixcoin has
shortcomings against active attacks in which the attacker
can compromise mixing service and inject fraudulent
transaction addresses to steal funds. Mixcoin has an
integrity issue in that the mixing service enabled
dishonest behavior. This paper proposes T-Mix, a
protocol that addresses Mixcoin’s shortcomings by
enhancing its availability and integrity using threshold
cryptography. We present Mixcoin’s threat model followed by a description of T-Mix.
Keywords
Blockchain Á Cryptocurrency Á Bitcoin Á Threshold
cryptography Á Information security Á
Privacy
1 Introduction
Blockchain is a distributed immutable digital ledger system
implemented without a central authority that is available
publicly to a community of users and enables them to record
transactions in ledgers. Each ledger comprises a chain of
data packages called blocks. Each block contains cryptographically signed transactions linked to the previous block,
which makes the system difficult to modify, which ensures
the integrity of the ledger (Yaga et al. 2019).
One major area of blockchain use is the financial field, in
which it is the main basis for many cryptocurrencies such as
Bitcoin. Bitcoin was invented by Satoshi Nakamoto in 2008
(Nakamoto 2008), and now has a market value of approximately 60.1 billion dollars (CoinMarketCap 2018). Other
cryptocurrencies such as Ethereum (2015) and Monero
(2014) also rely on blockchain.
Bitcoin is a decentralized digital currency based on
cryptographic proof, which enables it to implement a digital
cash system without the need for a trusted third party to
control the currency and eliminated the central single point
of failure of trusted dealers that exists in traditional systems.
Each Bitcoin user has a public and private key. The private
key is used to sign transactions, and the public key is used as
a Bitcoin address, which provides pseudonymity to the
users. The transaction can have multiple inputs and outputs.
Inputs and outputs are the source coin and beneficiary
addresses, respectively. All transactions are logged in a
public blockchain to prevent double-spending attacks (Narayanan et al. 2016).
1.1 Bitcoin Privacy
One of the essential features of Bitcoin protocol is the public
key anonymity as Bitcoin provides pseudonymity to users.
However, recently, some studies demonstrated that Bitcoin
users’ identities could be revealed by analyzing the stored
W. F. Aldamegh (&) Á L. A. Alsulaiman
College of Computer and Information Sciences,
Imam Muhammad Ibn Saud Islamic University,
Riyadh, Saudi Arabia
e-mail: wfdamee@sm.imamu.edu.sa
L. A. Alsulaiman
e-mail: laalsulaiman@imamu.edu.sa
© Springer Nature Switzerland AG 2020
M. Mateev and J. Nightingale (eds.), Sustainable Development and Social Responsibility—Volume 1,
Advances in Science, Technology & Innovation, https://doi.org/10.1007/978-3-030-32922-8_29
291
Service for Bitcoin
Wafa F. Aldamegh and Laith A. Alsulaiman
Abstract
Bitcoin is the first successful implementation of the
blockchain, which eliminates the role of trusted centralized settlement entities. Although Bitcoin was designed
with anonymity in mind, it has recently faced privacy
challenges as some users’ identities have been revealed
(Biryukov and Khovratovich 2014; Fleder et al. 2015;
Maesa et al. 2016, 2017) To address this issue, mixing
services are used in Bitcoin to increase user anonymity.
Mixcoin provides a centralized mixing service that
reduces the impact of blockchain transaction analysis
by hiding the links among transaction addresses to
preserve users’ anonymity. However, Mixcoin has
shortcomings against active attacks in which the attacker
can compromise mixing service and inject fraudulent
transaction addresses to steal funds. Mixcoin has an
integrity issue in that the mixing service enabled
dishonest behavior. This paper proposes T-Mix, a
protocol that addresses Mixcoin’s shortcomings by
enhancing its availability and integrity using threshold
cryptography. We present Mixcoin’s threat model followed by a description of T-Mix.
Keywords
Blockchain Á Cryptocurrency Á Bitcoin Á Threshold
cryptography Á Information security Á
Privacy
1 Introduction
Blockchain is a distributed immutable digital ledger system
implemented without a central authority that is available
publicly to a community of users and enables them to record
transactions in ledgers. Each ledger comprises a chain of
data packages called blocks. Each block contains cryptographically signed transactions linked to the previous block,
which makes the system difficult to modify, which ensures
the integrity of the ledger (Yaga et al. 2019).
One major area of blockchain use is the financial field, in
which it is the main basis for many cryptocurrencies such as
Bitcoin. Bitcoin was invented by Satoshi Nakamoto in 2008
(Nakamoto 2008), and now has a market value of approximately 60.1 billion dollars (CoinMarketCap 2018). Other
cryptocurrencies such as Ethereum (2015) and Monero
(2014) also rely on blockchain.
Bitcoin is a decentralized digital currency based on
cryptographic proof, which enables it to implement a digital
cash system without the need for a trusted third party to
control the currency and eliminated the central single point
of failure of trusted dealers that exists in traditional systems.
Each Bitcoin user has a public and private key. The private
key is used to sign transactions, and the public key is used as
a Bitcoin address, which provides pseudonymity to the
users. The transaction can have multiple inputs and outputs.
Inputs and outputs are the source coin and beneficiary
addresses, respectively. All transactions are logged in a
public blockchain to prevent double-spending attacks (Narayanan et al. 2016).
1.1 Bitcoin Privacy
One of the essential features of Bitcoin protocol is the public
key anonymity as Bitcoin provides pseudonymity to users.
However, recently, some studies demonstrated that Bitcoin
users’ identities could be revealed by analyzing the stored
W. F. Aldamegh (&) Á L. A. Alsulaiman
College of Computer and Information Sciences,
Imam Muhammad Ibn Saud Islamic University,
Riyadh, Saudi Arabia
e-mail: wfdamee@sm.imamu.edu.sa
L. A. Alsulaiman
e-mail: laalsulaiman@imamu.edu.sa
© Springer Nature Switzerland AG 2020
M. Mateev and J. Nightingale (eds.), Sustainable Development and Social Responsibility—Volume 1,
Advances in Science, Technology & Innovation, https://doi.org/10.1007/978-3-030-32922-8_29
291