A team of researchers has released a white paper for zk-starks, a much-anticipated blockchain privacy technology that has been lauded as a way to achieve zcash-level privacy without the risk of using a trusted setup.
One of the chief criticisms of using public blockchains like bitcoin to store monetary value is that they are the equivalent of making everyone’s bank account records publicly-accessible. Though the data is technically pseudonymous, it is often quite simple for governments and other powerful actors to associate addresses with their owners.
The zk-starks white paper, published on Jan. 12 by a team of researchers led by Eli Ben-Sasson of the Technion-Israel Institute of Technology, represents the latest attempt to use zero-knowledge (ZK) proofs to rectify the need for a public ledger to validate the integrity of the blockchain with the importance of protecting user privacy.
The white paper states:
“Human dignity demands that personal information, like medical and forensic data, be hidden from the public. But veils of secrecy designed to preserve privacy may also be abused to cover up lies and deceit by parties entrusted with Data, unjustly harming citizens and eroding trust in central institutions.”
The gripe with current ZK implementations — the most notable of which is the zk-snark technology currently used by the zcash cryptocurrency — is that they require the creation of a “master key.” The team behind zcash went to elaborate lengths to ensure that this key was not compromised during the launch of the network and was destroyed after its deployment.
However, the problem with such a trusted setup is that there is no way to conclusively verify that the key was destroyed without being compromised by a potentially hostile actor, who could use it to print new units of currency at will. The stakes of this trusted setup only increase along with zcash’s market cap, creating what some would term untenable systemic risk if zcash ever approached mass adoption.
“Public trust demands transparency from ZK systems, meaning they be set up with no reliance on any trusted party, and have no trapdoors that could be exploited by powerful parties to bear false witness,” Ben-Sasson and his co-authors continue, adding that unfortunately “no ZK system realized thus far in code (including that used by crypto-currencies like Zcash™) has achieved both transparency and exponential verification speedup, simultaneously, for general computations.”
Zk-starks (short for a zero-knowledge system that is a scalable and transparent argument of knowledge), if realized, could introduce transparency into the equation while also retaining the blockchain’s scalability.
The white paper includes a proof-of-concept in which police investigators prove that an allegedly-corrupt presidential candidate’s DNA does not appear in the department’s forensic DNA database, without compromising the integrity or confidentiality of either the candidate’s DNA or the database.
However, as the paper notes, zk-snarks are “roughly 1000x shorter” than zk-stark proofs, so more research will be needed to mitigate this problem through shorter proofs or another solution.
Notably, researchers are also exploring ways to implement ZK proofs into Bitcoin. Stanford University’s Applied Cryptography Group, for instance, recently released a white paper for Bulletproofs, a ZK protocol that could be used to increase the privacy of bitcoin transactions without a trusted setup.
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