Synthid is a watermark which indicates the video is AI-generated, not a digital signature indicating it's real. Completely different use case and threat model.
I'm not aware of any secure digital signature schemes that don't require the thing they signed to be bit-for-bit identical to pass verification. There are perceptual hashing algorithms that could theoretically be used to build such a scheme, but such hashes are not second preimage resistant, so someone could create a modified video that still passes signature verification.
alt Hacker News
Synthid is a watermark which indicates the video is AI-generated, not a digital signature indicating it's real. Completely different use case and threat model.
I'm not aware of any secure digital signature schemes that don't require the thing they signed to be bit-for-bit identical to pass verification. There are perceptual hashing algorithms that could theoretically be used to build such a scheme, but such hashes are not second preimage resistant, so someone could create a modified video that still passes signature verification.