In Eva, the publisher decides to make a sequence E of edits to a video V, resulting in a new video V'.
Eva allows the publisher to create a proof of the following facts:
- The video V' presented to the user has been derived from an original video V by applying the edits E.
- The original video V was signed by the recording device.
The user receives the new video V' and the edits and the proof of the statements above. Note that the user does not receive the original video V, since that may have confidential redacted information.
This kind of proof is called a
zero-knowledge proof because it does not contain any information about the confidential ingredient V. The proof convinces the user that such a V exists, without giving them the ability to reconstruct it.
Our paper formalises the notion and security model
of proofs of video authenticity and describes the cryptographic video authentication protocol (called Eva), which supports
lossy codecs and arbitrary edits and is proven secure under
well-established cryptographic assumptions.
Compared to previous cryptographic methods for image authentication, Eva is
not only capable of handling significantly larger amounts of
data originating from the complex lossy video encoding but also
achieves linear prover time, constant RAM usage, and constant
proof size with respect to video size. Generating zero-knowledge proofs is known to be slow, but our implementation of Eva
integrates the Nova folding scheme and other
optimizations to make Eva practical. For a 2-minute HD
(1280 × 720) video encoded in H.264 at 30 frames per second,
Eva generates a 448 byte proof in about 2.4 hours on consumer-grade hardware at 2.6 μs per pixel, surpassing state-of-the-art
cryptographic image authentication schemes by more than an
order of magnitude in terms of prover time and proof size.
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