Decentralized Systems

Decentralized systems can reduce trust requirements and reliance on central actors by distributing control across multiple entities. Decentralization can offer many advantages, such as higher user autonomy, improved robustness, and more openness to innovation.

Perhaps the best-known representative is blockchain technology. Blockchains with smart contract support, such as Ethereum, enable new forms of financial applications. However, the widespread adoption of digital currencies also presents challenges. Higher transaction volumes demand more scalable protocols to improve throughput, but moving from sequential to concurrent transaction execution remains difficult because transactions often have complex dependencies on multiple smart contracts. Another concern is privacy leakage from pseudonymous transactions. For UTXO-based systems, sophisticated cryptographic solutions like Zerocash can provide anonymity but incur significant computational overhead. For account-based systems, anonymous solutions often impair usability because they require rate limits or explicit acceptance of incoming payments. Advances in privacy can also create tensions with efforts to combat money laundering and terrorist financing. Supporting regulatory requirements is therefore essential to reconcile privacy with security.

Beyond financial applications, decentralization also plays an important role in electronic identity systems. Users can store credentials locally and prove attributes about themselves without disclosing unnecessary information or involving identity issuers in the process. Compared to traditional identification via video or passport scans, electronic identities create opportunities for improved security and privacy. Achieving these benefits requires solutions to open problems, such as combining multiple credentials in a single proof and binding digital identities to physical persons for unlinkable in-person verification.

In our research, we investigate the limitations of current decentralized systems and develop novel solutions with improved security, privacy, and performance guarantees. Our recent results include designs for anonymous online and offline central bank digital currencies that support a wide range of regulatory policies while remaining practical to deploy.

For more information on our research on decentralized systems, please visit the System Security website.

Selected Publications

Carolin Beer, Sheila Zingg, Kari Kostiainen, Karl Wüst, Vedran Čapkun, and Srdjan Čapkun
Payoff: A regulated central bank digital currency with private offline payments
in ACM Asia Conference on Computer and Communications Security (AsiaCCS’26)

Karl Wüst, Kari Kostiainen, Noah Delius, and Srdjan Čapkun
Platypus: A Central Bank Digital Currency with Unlinkable Transactions and Privacy-Preserving Regulation
in ACM Conference on Computer and Communications Security (CCS ’22)

Karl Wüst, Loris Diana, Kari Kostiainen, Ghassan Karame, Siniša Matetić, and Srdjan Čapkun
Bitcontracts: Supporting Smart Contracts in Legacy Blockchains
in Network and Distributed System Security Symposium (NDSS ’21)

Karl Wüst, Siniša Matetić, Silvan Egli, Kari Kostiainen, and Srdjan Čapkun
ACE: Asynchronous and Concurrent Execution of Complex Smart Contracts
in ACM Conference on Computer and Communications Security (CCS ’20)

Vasilios Mavroudis, Karl Wüst, Aritra Dhar, Kari Kostiainen, and Srdjan Čapkun
Snappy: Fast On-chain Payments with Practical Collaterals
in Network and Distributed System Security Symposium (NDSS ’20)

Karl Wüst, Siniša Matetić, Moritz Schneider, Ian Miers, Kari Kostiainen, and Srdjan Čapkun
ZLiTE: Lightweight Clients for Shielded Zcash Transactions using Trusted Execution
in Financial Cryptography and Data Security (FC ’19)

Karl Wüst, Kari Kostiainen, Vedran Capkun, and Srdjan Čapkun
PRCash: Fast, Private and Regulated Transactions for Digital Currencies
Financial Cryptography and Data Security (FC ’19)

Moritz Schneider, Siniša Matetić, Ari Juels, Andrew Miller, and Srdjan Čapkun
Secure Brokered Delegation Through DelegaTEE
in IEEE Security & Privacy (S&P ’19)