C2PA Timestamping Vulnerability Allows Manipulation of Content Authenticity

C2PA and Timestamping

The C2PA standard incorporates two primary signatures for content authenticity: a "claim" signature and a Time Stamp Authority (TSA) signature. The claim signature, often generated by the capturing device, asserts details like capture time and GPS coordinates. However, previous research has shown that this claim signature can be easily forged in implementations like the Google Pixel Camera app.

The TSA signature is considered more robust, as it relies on a remote server using the RFC 3161 protocol to independently verify that a hash of the content existed at a specific timestamp. This mechanism is designed to prevent devices from falsely asserting their own time.

The "Spec Footgun" Vulnerability

Despite the security provided by the TSA, a vulnerability described as a "spec footgun" exists within the C2PA specification itself. This allows for the manipulation of timestamps, even when the TSA mechanism is functioning as intended. The core issue lies in how C2PA handles arbitrary "exclusion" within its metadata structure.

Impact on Content Authenticity

This vulnerability means that content can be made to appear as if it existed at an earlier time than its actual creation. This undermines the fundamental purpose of C2PA, which is to provide cryptographically verifiable authenticity for digital content. The ability to manipulate timestamps could have implications for verifying the origin and timeline of images, videos, and other digital assets.