Checksums in Browser Uploads: What They Prove and What They Do Not

Short summary

A detailed technical analysis of checksums in browser upload systems, clarifying what digests prove (byte equality) and what they do not (provenance, consent, safety). It covers choosing the right byte boundary to hash, incremental hashing for large files, avoiding information leakage from deduplication, and proper digest storage with algorithm versioning. The author discloses a commercial interest via Gathmo.

• •Checksums prove byte equality, not authorization, provenance, or consent
• •Hash the right byte boundary: browser source vs assembled storage object vs transcoded derivative
• •Avoid raw digests as public keys and prefer deduplication within event or owner boundaries

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