Blockchain Privacy: Tools, Protocols, and the Road Ahead

Blockchain is often floated as a solution for protecting users’ privacy. While blockchain’s founding ethos does promote returning power to individuals from third-party intermediaries, the technology itself isn’t inherently private. In fact, quite the contrary – blockchains were built for transparency, not secrecy. Every transaction, wallet address, and contract interaction is visible in plain text onchain. While pseudonymity offers a thin veil, it can be penetrated relatively easily using statistical analysis and data clustering tools.

True blockchain privacy isn’t just about encrypting data, it’s about accounting for every way that information might escape, including through a system’s performance, structure, or user behavior. This is why privacy on blockchain is both critical and challenging: users deserve confidentiality without sacrificing the trustless transparency that makes the technology powerful. It is essential for the blockchain community to actively define what privacy should guarantee, and for developers to design systems that protect users by default.

Understanding why blockchains aren’t inherently private

The problem of blockchain privacy is structural. Traditional blockchains store all data on a public ledger, meaning anyone can:

• Track transactions: Every transaction on Bitcoin or Ethereum leaves a trace, including details such as the addresses of the sender and recipient and the amount transferred. Even with pseudonymous addresses instead of personal names, those addresses can be tracked and used to develop a picture of a user’s financial behavior, or to estimate an individual’s net worth, among other things.

• Link wallets to real identities: once a blockchain user interacts with a platform or dapp that is subject to regulation or KYC, the user’s pseudonymity starts to erode. For example, if a user sends Bitcoin to or from a KYC-verified exchange, the user’s wallet is tied to a verified identity. Thus, it becomes possible to connect personal data with onchain financial behavior.

• Reconstruct full transaction histories: One of blockchain’s central features is its immutability. Thus, once a wallet address is tied to a personal identity, it is possible to track the entire history of a user’s transactions onchain. This feature is necessary for transparency and trustlessness, but it does not allow for discretion or privacy.

How blockchains can become private

There are three main approaches to bringing privacy to blockchains:

1. Protocol-level privacy

Zcash, Monero and Aztec enforce privacy through their protocols. Monero protects transfers by default. Zcash supports shielded and transparent transactions, while Aztec supports private and public contract state.

• Pros:
  • Native privacy: Protocol rules protect private activity. The protection depends on the transaction type and application.
  • Protocol-native enforcement: No need for third-party tools or external mixers.
  • Auditability with selective disclosure: Users can reveal data selectively when needed, for compliance or verification purposes, for example.
• Cons:
  • High computational cost: Generating and verifying zero-knowledge proofs can be heavy on both the user and the network.
  • Limited scalability: Full privacy at the protocol layer can slow down throughput and increase fees.
  • Complex user experience: Managing shielded vs. transparent addresses (as in Zcash) can be confusing and cause accidental privacy leaks.

2. Add-On Privacy (Application-Level)

Networks like Ethereum add privacy through external tools such as Tornado Cash, Privacy Pools, or confidential ERC-20s. Rather than altering the base protocol, these solutions offer privacy for users or dapps that opt-in.

• Pros:
  • Flexibility: Users can choose when and how to use privacy tools.
  • Composability: The tools can be integrated with existing DeFi, NFTs, and wallets without forking the network.
  • Rapid innovation: New privacy layers can be deployed without consensus changes.
  • Interoperability: Builders and devs can mix and match tools across chains.
• Cons:
  • Compliance and legal risk: Protocols like Tornado Cash have faced sanctions and shutdowns for allegedly facilitating illicit activity.
  • Traceability: Advanced analytics sometimes deanonymize users.
  • Fragmented UX: Users must manage multiple tools, bridges, and proofs manually.

3. Hybrid Approach

A hybrid model combines protocol-level efficiency with app-level flexibility. This model allows users, devs, and dapps to customize their level of confidentiality. It integrates privacy through client-side proving and onchain verification, wallet integration for seamless user experiences, and composability with existing dapps and DeFi infrastructure.

• Pros:
  • Best of both worlds: Combines scalability, efficiency, and privacy.
  • Client-side control: Users retain control of sensitive data and proofs before publishing to the chain.
  • Seamless UX: Wallets and dapps can abstract privacy complexity behind familiar interfaces.
  • Regulatory flexibility: Privacy can be made compliant or auditable depending on context.
• Cons:
  • Implementation complexity: Hybrid systems require coordination between protocol, wallets, and dapps.
  • Developer overhead: Building with privacy primitives adds complexity and testing requirements.
  • Evolving standards: Best practices are still developing.

Below, we discuss several examples that represent the hybrid model.

Validium

At the protocol layer, Validium exemplifies how hybrid systems achieve privacy without compromising performance. Unlike a traditional zk-rollup, which publishes transaction data directly onchain, Validium allows users to transact offchain, and a cryptographic proof attesting to the validity of the result is verified onchain. Every batch of transactions is cryptographically verified using zk proofs, ensuring that the offchain data hasn’t been tampered with. This method improves scalability and privacy by keeping sensitive information off the public ledger, while ensuring it is secure. In short, Validium embodies the “private by design, verifiable by default” ethos.

Self-custody wallets

At the user interface level, self-custody wallets implement client-side privacy, allowing users to generate and manage their proofs, keys, and encryption locally, without ever exposing sensitive information. Self-custody over one’s private keys also reduces the risk of unauthorized access and data breaches often associated with custodial wallets. While these wallets don’t offer complete anonymity, they improve privacy by removing the need for external management.

When integrated with zk-proving frameworks like Noir or POTC (Proofs on the Client), self-custody wallets become privacy enablers, not just asset managers.

Why Starknet is becoming the best place for privacy

STARKs and STRK20 on Starknet

Starknet is a public blockchain built on STARKs (Scalable Transparent Arguments of Knowledge), a proof system pioneered by StarkWare. STARKs allow computation to be proved offchain and verified efficiently onchain, without a trusted setup.

Developed by StarkWare, STRK20 is a privacy pool for ERC-20 assets on Starknet. It uses the Stwo STARK prover to generate zero-knowledge proofs for private transfers. Users can shield ERC-20 tokens and transfer them privately through compatible wallets. The proofs verify that each transfer follows the pool’s rules.

STRK20 follows the hybrid approach described above. Its privacy pool is a smart contract that uses Starknet’s protocol-level proof verification. Developers can build applications using the pool, with privacy determined by each application’s design.

Company balances and payments

STRK20 can protect a company’s shielded balances and private transfer amounts from public observers. Deposits and withdrawals remain public, and interactions with external applications can expose activity and amounts.

Opening a new transfer channel can reveal the recipient’s address. Transaction timing and recognizable payment patterns can also weaken privacy. Companies need to assess the wallet, application and payment flow they plan to use.

Auditor access

At registration, users must store an encrypted copy of their private viewing key onchain for a designated auditor. Under the protocol’s compliance model, that auditor can recover the key to trace the user’s incoming and outgoing pool activity when authorized.

The viewing key can reveal the user’s associated transaction history. It cannot authorize spending. The required registration is separate from a company choosing to share records with its accountant.

Building privacy applications on Starknet

Developers can use STRK20 to add shielded ERC-20 balances and private transfers to applications on Starknet, with private activity verified using STARKs.

For dapps, the Starknet Wallet API lets applications request private actions through the user’s wallet. Teams building privacy wallets or backends can use the STRK20 Privacy SDK to manage viewing keys, discover private balances and coordinate proof generation.

Start with the STRK20 builder hub to choose your integration route and find starter kits and developer resources. STRK20 by Example provides practical walkthroughs for wallet integration and SDK development, including Cairo anonymizer contracts for DeFi integrations.

Existing privacy solutions on Starknet

From infrastructure to applications, the Starknet ecosystem is committed to the idea that privacy and transparency can coexist, and that true decentralization requires both. The Starknet ecosystem already hosts a growing lineup of privacy-focused projects that explore different aspects of privacy, some of which were discussed above:

• Mist.cash – combines private payments and privacy pools in one UX-friendly package
• Tongo – enables confidential ERC20s, allowing builders to deploy private tokens easily
• 0xbow Privacy Pools – ad-hoc privacy mixing with on-chain composability
• Typhoon Network & Visoft Privacy Pools – experimental privacy solutions pushing the boundaries of decentralized privacy

The Starknet Foundation and StarkWare actively support responsible privacy teams through grants, technical guidance, and collaboration with tooling frameworks like Noir, Garaga, and Cairo. As new projects emerge, Starknet continues to solidify its position as the most advanced privacy-ready Layer 2 in the Ethereum ecosystem, balancing verifiability, performance, and confidentiality.

Privacy on Starknet Today

• • STRK20 privacy hub brings together technical guides, application examples and resources for developers.
  • How STRK20 works explains how ERC-20 assets enter the privacy pool and move through private transfers.
  • What works today lists current actions, integration routes and limitations in the STRK20 hub.
  • Formal Verification explains which properties of STRK20’s protocol model have been proved in Lean.

Not investment advice; do your own research. Engagement carries risk, including risk of loss. Privacy on Starknet is provided by protocols such as STRK20 and by privacy applications.