Quote from: Husna QA on March 22, 2020, 05:05:54 PM

10. Mixing Service
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There are other methods to deal with privacy issues in Bitcoin transactions, namely, by using a mixing service (randomization).

Bitcoin Mixing²⁰

These services have different methods for mixing users' Bitcoin. However, the methods they use can be classified into two groups ²¹.

In the first group, the service asks users to send bitcoin into a virtual wallet that is controlled by the service, so users can retrieve their bitcoin to sent to another Bitcoin address. The service provider will exchange the user's Bitcoin for another bitcoin that has no connection with his previous bitcoin. If the user wants to pay a coin to another party, they can enter the destination address to be paid by the service provider.

The second group is a service that combines several transactions into a significant transaction using a concept like CoinJoin (the mechanism combines several similar transactions into a transaction that consists of many inputs and outputs).

When users use services like this, they have to pay a bitcoin service fee to the service manager in the amount between 0.5% to 3%. Although services like this might increase anonymity, there are also risks borne by users, because they cannot control their bitcoin when they have sent the bitcoin to the manager's bitcoin address. It means that when the service manager acts fraudulently by stealing the user's bitcoin, the user cannot do anything else because all bitcoin transactions cannot be canceled.

In the thesis of Felix Maduakor ²⁰ on Mixing Services / Anonymous Bitcoin Transactions, pages 18-20, the Mixing Method divided into three categories
https://www.dropbox.com/s/3yapwyfz72tvswh/BA_mixing_services.pdf?dl=0
The following is a summary of these categories:

1. Decentralized Mixing (P2P Mixing)

A figure of P2P Mixing Service

Several scientific papers, such as or about algorithms, which allow the transfer of bitcoin anonymously, have been published. Some of these algorithms have been implemented in different cryptocurrency by default (example: Zerocash²²), but at the time of writing [-thesis-], no approach has been widely adopted in the Bitcoin network. Unlike Centralized Mixing Services (CMS), P2P Mixing must be implemented in Bitcoin wallet software so that users can access it.

2. Centralized Mixing Services (CMS)

A figure of Centralized Mixing Services

Centralized Mixing Services (CMS) are usually run by commercial website providers who advertise that their services can anonymize Bitcoin transactions. CMS usually charges fees up to 3% of the initial amount of coins that have not been sold. Often the P2P mixing algorithm is used internally by CMS.

3. Off Chain Mixing

The public can access every transaction sent through the Bitcoin network through the Bitcoin blockchain. However, recently there have been many scientific efforts to find solutions to send and receive Bitcoin transactions without the need to publish them on the blockchain.
Among the implementation solutions for this problem include Lightning Network.
Lightning Network leads to transactions that are almost instant and may eliminate transaction costs.

Quote from: theymos on May 22, 2019, 10:18:50 PM

-snip- Anonymity is very difficult, especially with blockchain-based systems where so much data has to be public, but also in other areas (eg. there are several known weaknesses with Tor). You should always operate with the expectation that any anonymity system you use will eventually fail you. If you're ever confident in your anonymity, then you're wrong. ...

Quote from: madu on March 05, 2019, 09:30:35 PM

-snip- that even though a mixing service/a mixing algorithm might seem to be reliable at the moment, through a single leak/implementation fault, an attacker could be able to deanonymize any past transaction which has been processed by the mixing services. Even though the leak/implementation fault gets fixed by the service, every transaction which has been processed prior to the fix is irreversible vulnerable. -snip-

Comparison between Bitcoin Mixer and CoinJoin²³:

Quote

#	Mixer	CoinJoin
1	Closed-source and the system cannot be verified.	Open-source and can't be verified by the system (in general).
2	A mixer controls the coin.	The user controls the coin
3	Privacy is lost if the mixer keeps the mixing activity or the mixing method is wrong.^[24]	Privacy is lost if CoinJoin's implementation is incorrect.

Some Bitcoin Mixers Bitcoin Tumblers website links compiled by LeGaulois²⁵:
https://bitcointalk.org/index.php?topic=2827109.msg28964833#msg28964833

Reference:
20. Anonymous Bitcoin Transactions. Felix Maduakor
   https://www.dropbox.com/s/3yapwyfz72tvswh/BA_mixing_services.pdf?dl=0
21. Dimaz A.W. & Oscar D., Blockchain dari Bitcoin untuk Dunia, pages 109-110, 2017: Jasakom
22. Eli Ben Sasson, Alessandro Chiesa, Christina Garman, Matthew Green, Ian Miers, Eran Tromer, and Madars Virza.
   Zerocash: Decentralized anonymous payments from bitcoin.
   In Security and Privacy (SP, 2014 IEEE Symposium on, pages 459-474. IEEE, 2014
23. https://bitcointalk.org/index.php?topic=5125545.msg50811291#msg50811291 - ETFbitcoin
24. Breaking Mixing Services - madu
25. 2019 List Bitcoin Mixers Bitcoin Tumblers Websites - LeGaulois
- [Guide] Decent mixing methods - theymos
- What is Bitcoin Mixer? - RapTarX
- Anonymous Bitcoin Transactions. P. Martin and A. Taaki. (2013, August 25, 2015/0)
- CoinJoin: Bitcoin privacy for the real world by gmaxwell
- Other references look at post #1