Miti Mazmudar and Ian Goldberg create Mitigator, a new system to protect users’ online data

Monday, May 4, 2020

Computer scientists at the Cheriton School of Computer Science have developed a new system that helps Internet users ensure their online data is secure. Called Mitigator, the software-based system includes a plugin that users can install in their browser, which will give them a secure signal when they visit a website verified to process its data in compliance with the site’s privacy policy.

“Privacy policies are really hard to read and understand, and now with COVID-19 so many people are doing so much more online that privacy policies are more important than ever,” said Miti Mazmudar, a PhD candidate in the Cryptography, Security, and Privacy (CrySP) research group.

Although research has been conducted into alternative representations of privacy policies, the systems that have been developed do not determine whether website providers adhere to the data handling practices outlined in their privacy policies.

“What we try to do is have a compliance system that takes a simplified model of the privacy policy and checks the code on the website’s end to see if it does what the privacy policy claims to do,” Miti Mazmudar continued. “If a website requires you to enter your email address, Mitigator will notify you if the privacy policy stated that this wouldn’t be needed or if the privacy policy did not mention the requirement at all.”

Mitigator can work on any computer, but the companies that own the website servers must have machines with a trusted execution environment — a secure area of modern server-class processors that guarantees the protection of code and data loaded in it with respect to confidentiality and integrity. The Mitigator implementation is prototyped using the Intel Software Guard Extensions (SGX) trusted hardware platform.

Mitigator’s main contribution is in designing an architecture that uses an underlying trusted hardware platform to run a program — called the decryptor — that hands users’ data only to a target program that has been determined to be compliant with a privacy policy model. As both of these programs are run on a trusted hardware platform, users can verify that the decryptor is indeed the correct, unmodified program.

“The big difference between Mitigator and prior systems that had similar goals is that Mitigator’s primary focus is on the signal it gives to the user,” said Ian Goldberg, a Professor at the Cheriton School of Computer Science and the Canada Research Chair in Privacy Enhancing Technologies.

“The important thing is not just that the company knows their software is running correctly; we want the user to get this assurance that the company’s software is running correctly and is processing their data properly and not just leaving it lying around on disk to be stolen. Users of Mitigator will know whether their data is being properly protected, managed, and processed while the companies will benefit in that their customers are happier and more confident that nothing untoward is being done with their data.”

Block diagram of the Mitigator system

Block diagram of the Mitigator system. Mitigator has three stages. The first stage runs as a website’s source code is being developed. During this stage the verifier enclave checks the source code and privacy policy for compliance. If the code complies with the privacy policy, it outputs a signed target enclave. If the code does not comply with the privacy policy, developers are expected to modify their source code and privacy policy and rerun the system until it passes as compliant.

The second stage occurs once the target enclave is ready to be deployed. Here, the decryptor enclave conducts local attestation with both enclaves.

The third stage refers to runtime interactions between the website user, target, and decryptor enclaves. In this stage, the website user passes encrypted form field data to the target enclave, which in turn securely hands it over to the decryptor enclave.


A paper detailing this study, titled “Mitigator: Privacy policy compliance using trusted hardware,” was written by Miti Mazmudar and Ian Goldberg. Their paper was accepted for presentation at PETS 2020, the 20th Privacy Enhancing Technologies Symposium, which will be held virtually from July 14 to 18, 2020. The paper will be published in the open-access journal Proceedings on Privacy Enhancing Technologies (PoPETs).

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