Early Privacy: Mixers, CoinJoin, and Stealth Addresses.
When Bitcoin appeared in 2009, it was often called an “anonymous currency.”
However, as the ecosystem developed, it became clear that Bitcoin is not truly anonymous, but pseudonymous - all transactions are permanently visible on the blockchain, and anyone can trace the flow of funds from one address to another.
This realization sparked the emergence of early privacy solutions, which aimed to partially obscure transactions long before zk-protocols, FHE, and TEE computations were available.
Early solutions included:
Cryptocurrency Mixers
CoinJoin
Stealth addresses
1. Mixers: The First Attempt to Hide Traces.
A mixer is a service that accepts users’ coins, “shuffles” them with other participants’ coins or its own liquidity pools, and then sends back new coins that are not directly linked to the original transactions.
The main idea:
Make it impossible to determine which inputs correspond to which outputs.
A user sends funds to the service.
The mixer aggregates deposits from multiple users.
After some time, it sends back equivalent amounts to each participant, but from completely different addresses.
Problems with mixers:
Centralization → the service could steal funds.
Log leaks → some mixers compromised user privacy.
Legal risks → governments started treating mixers as money laundering services.
Mixers were an important step for privacy but had serious weaknesses, leading the industry to develop cryptographically grounded solutions.
2. CoinJoin: Decentralized Mixing
CoinJoin is a method where multiple users combine their transactions into one, making it impossible to determine which input belongs to which output.
Each transaction can be easily linked to its sender.
With CoinJoin:
A single large transaction is created that combines all inputs and outputs.
Inputs:
• 1 BTC from A
• 1 BTC from B
• 1 BTC from C
Outputs:
• 1 BTC to X
• 1 BTC to Y
• 1 BTC to Z
All outputs are equal, and it is impossible to determine which input corresponds to which output.
Although CoinJoin has advantages - decentralization and no need for trust, there are critical disadvantages: vulnerability to graph analysis, Sybil attacks, and legal and regulatory issues.
3. Stealth Addresses: Hiding the Recipient
If you know someone’s public address, you can see all incoming and outgoing transactions for that address forever.
Stealth Addresses solve this problem
The sender generates a unique one-time address for each transaction.
The recipient uses their private key to scan the blockchain and determine which addresses belong to them.
Result: no one else can link transactions to the recipient's real public address.
Stealth addresses became an important historical step in the development of privacy (For example, with Monero), but at that time the technology had disadvantages:
Increased network load
A more complex user interface for users
Some early implementations had weaknesses in cryptography
Although the methods described above often only provide an illusion of privacy, as they are more of an attempt to hide data within the system, they nevertheless represent an important step in the development of privacy-enhancing technologies and have led to the emergence of:
Privacy-focused cryptocurrencies
zk-protocols
Private computations (TEE, MPC, FHE)
As cryptocurrencies develop, it is becoming increasingly clear that:
Users need privacy
Open blockchain data can be dangerous
Privacy is not a matter of “criminality” but of security, freedom, and data protection.
Privacy is essential for mass adoption.
All of this has contributed to the emergence of solutions such as
Inco network - a modern layer of confidentiality for Web3.
In the following sections, we will continue to discuss the evolution of privacy and take a closer look at more modern solutions.