Updated: November 23, 2020.
A draft report from the European Commission (EC) was leaked in September 2020, entitled “Technical solutions to detect child sexual abuse in end-to-end encrypted communications,” that proposed different ways to moderate content shared in end-to-end encryption messaging systems.
But there is much that the European Commission’s leaked report got wrong. The Global Encryption Coalition (GEC), led by CDT, the Internet Society, and Global Partners Digital to promote and defend encryption in key countries and multilateral gatherings where it is under threat, leveraged its group of expert members to rebut the claims of the draft paper in a detailed technical analysis released today.
Highlights from that analysis include a breakdown of the three types of methods it proposes to use to access end-to-end encrypted content:
- Traditional backdoors: A communications platform that allows third party access to the content of encrypted communications. For instance, key escrow, access to a server where the data is held upon receipt, or a “middle-box” which decrypts the data at a central server and then re-encrypts it for sending to the intended recipient.
- Client-side scanning: Referred to in the leaked report as “device related,” these access methods scan message contents on the user’s phone, tablet or mobile. Videos and images, for example, are scanned for matches against a database of prohibited content before, and sometimes after, the message is sent to the recipient. If the message’s contents match known prohibited content, the full message would be sent to a third party for manual review.
- Secure enclaves and homomorphic computation: Referred to in the Draft as “server related” and “encryption related,” an encrypted message’s content can only be “seen” by the computation in a server or on the user’s device. If the message is found to contain prohibited content it will be forwarded to a third party for manual review.
The technical report is unequivocally clear about the mainstream technical expert consensus on backdoors, and how they are likely to become discovered and utilized by adversaries. Furthermore it directly challenges manual review processes, which are necessary for content moderation, but by being introduced directly put user safety and privacy at risk.
The technical report also demonstrates that even though the process for client-side scanning means prohibited content is scanned on the user’s device, the database of hashed images is most likely to be held at a central server, due to technical realities, and the hash of each image the user wants to send will be known by the server – creating a target for bad actors.
Additionally, the technical experts’ analysis also highlights that secure enclaves, by allowing private user data to be scanned via direct access by servers and their providers, break the privacy expectations of users of end-to-end encrypted communication systems, as well as preserve the manual review step for hash matches.
Poignantly, the analysis concludes, “This leaked report fails to outline the serious risks of requiring communications service providers to detect prohibited content. These requirements would force service providers to undermine the security of their end-to-end encrypted services, jeopardizing the safety of the billions of people who rely on them each day.”
You can view the analysis and its dozens of expert signatories on the GEC website here: https://www.globalencryption.org/2020/11/breaking-encryption-myths.