Aarhus University Seal / Aarhus Universitets segl

Cryptographic Primitives for Blockchains

Cryptographic Primitives for Blockchains

  • The art of validating data and keeping them private

Blockchain technology allows different users to keep a replicated copy of a database containing immutable data, even in the presence of corrupted parties.

This research topic is concerned with the data that will be stored on the blockchain, how to validate its origin, and how to make sure that the right individuals can access the data they are supposed to, while ensuring that no individual can access data they are not supposed to. This should be done without leaking too much information about the users.

When using Blockchains for economic transactions, a fundamental cryptographic primitive is digital signatures. A digital signature, much like an old-fashioned signature, allows a user A to take ownership of some statement (for instance “I want to transfer 100 coins to user B”), in such a way that everyone else can recognize an authentic signature (by matching the signature against the public key of user A). At the same time, no one should be able to forge a signature (thus pretending to be someone else), and a user issuing a signature should not be able to later repudiate that they signed some message (‘“it wasn’t me!”). Much research is still needed in the world of digital signatures. In many early Blockchain projects, such as Bitcoin, money has been stolen due to problems with the used digital signature schemes (or their implementations). A particular topic of interest is the design of post-quantum signature schemes, i.e., signature schemes, which will also be secure if and when quantum computation will become a reality.


Another important research topic concerns the cryptographic tools that need to be developed to ensure that certain data is only available to authorized parties in the context of Blockchain. In early Blockchain projects, such as Bitcoin, Ethereum, etc., all transactions were public and available online for everyone to see. This is clearly undesirable: A company paying their employees in Bitcoins would easily be able to monitor how and when their employees spend their money. At the same time, and perhaps counterintuitively, cryptocurrencies have been used for illegal activities thanks to their “pseudonymity”. The research center will study solutions to the above problems. Thus, novel tools will be designed in order to guarantee the confidentiality of transactions, while at the same time allowing for accountability.In a nutshell, this means that no one should be able to learn information about one’s financial activities or wealth, while at the same time we need to guarantee that, in necessary cases, a police agency or a tax authority, given a legal mandate, should be able to reconstruct someone’s financial transactions to allow investigation of criminal activities. This research goes hand-in-and with the research under the topic Zero-Knowledge.