i do wonder, that in the age where we have image and video creation out of the bag, whether or not this will result in whole classes of evidence becoming completely unreliable.
Humans are flawed but that doesn't mean everyone in the jury thinks TV is real.
But I don't know of a cryptographic mechanism to ensure that a digital image is not more recent than a particular time
That would be a use case for a block chain. But I still don't understand how you are securing the integrity of the validity of the certificate stating the authenticity of the media. I only understand you are stamping media with a "at least as old as [timestamp]
[0] https://csrc.nist.gov/projects/interoperable-randomness-beac...
Embedding a public random number also doesn't resist tampering, unlike signed timestamps.
The image contains the previous block’s hash.
Wouldn’t this establish both a lower bound and an upper bound on the time the image could have been produced?
Back when I was on Twitter and following a lot of infosec accounts, it was quite common to see tweets that were just a hash. Sometimes they'd have an explanation "Zero click RCE in Android 10 - {hash}"
In the past I've used gmail for this internally - email a hash of something critical (logs, configurations, decision docs, etc) to a dedicated gmail account - relying on the in feasibility of "faking" the date/time once it's onb Google's servers.
The important thing here would be to make sure those hashes are published somewhere where its technically infeasible for the police to change it after the fact, so not on a platform the police run or p-aid for (or that is run or paid for by an organization that the police can request or coerce the operators to make changes).
As a community service you need them to have enough scale that no individual hash or source can be tampered with without being likely to become known as unreliable to everyone else as well ala certificate transparency records.
(You could probably just bootstrap let's encrypt for this - issuing a certificate you use to sign a bunch of data would stamp several minimums on the order anything could have happened).
Many (most?) blockchain mechanisms include a timestamp in each transaction on the chain, so while multiple records from the same owner prove little (the timestamps could be faked over a given period of time) the interaction with the wider network and the chain would give some confidence that the record happened between within a small amount of time.
The other possibility, that doesn't require a chain with many independent active participants, is to have things signed by an external trusted authority. Submit a hash of the content and appropriate metadata to them, and have them sign it with a signing timestamp. I've considered abusing ACME certificates for document signing like that: the hash of content (or some signature based upon it) becomes the subdomain to sign¹ and you get a certificate that even after expiry is evidence that the CA saw that value at the signing timestamp. Note of the signing will also be in the public certificate transparency log. This wouldn't, on its own, prove anything about the authenticity of the content, that could have been doctored before signing, but it does prove that the content+metadata existed at that time (so might be more useful in copyright claim type cases, or agreed contract situations where all parties have signed the content and the signatures are included in the metadata, than for proving authenticity).
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[1] based64²-ed with non-alphanumeric characters removed and truncated³ to fit or split, so acodha3sf7whsrhtqestkabtx0b4bbhyveee0ajnrpqcuxrjjvmhsujgcex.domain.tld or acodha3sf7whsrhtqestkabtx0b4bbhyveee0ajnrpqcuxrjjvmhsujgcex.w5jmmkpmyfgshx2jecsfordpnq.domain.tld
[2] names not being case-sensitive drops some of the entropy, if that is a concern use a 32-bits-per-character encoding instead and have names twice as long
A TXT record may be used in the signing process if using DNS verification, but you are getting a certificate for the name overall so using an A record to hold the hash you are looking to certify does the trick, then if you want to use HTTP-01 for verification rather than an extra DNS record you can.
Took about six months for someone to crack the hash.
I suspect that the cops wouldn’t like the chain public, though.
An attacker altering the ledger would still require compromising an unreasonably large number of independent groups at once, and even then the rest would be able to clearly see that some unusual and suspicious event occurred.
By limiting membership a bunch of problems simply vanish, like long-clearing times, wasting hardware on mining, vulnerability to foreign botnets, etc.
[0] A blockchain is distinguished by its core requirement, from which a cascade complexity flows: Uncontrolled node membership. Don't be fooled by people pitching "private blockchain", its a contradiction in terms designed to rehabilitate hype, like "multi-sample Theranos test" or a bicycle as "Segway passively stabilized inline wheel model."
if it is mandated that every photo or video taken for the possible use in evidence is notarized at the time of acquisition, any fabrication would necessitate total premeditation. that is, the fabricators would need to know ahead of time what they were pursuing and what evidence they would need. this seems like a very costly barrier.
for example, altering security footage would require some fantastical elements: a real-time system of ingesting real footage and altering it in real-time to slip it into the notarization pipeline within the error margins.
requiring that any equipment that produces acceptable evidence stream commitment hashes in real-time to public append-only repositories would be an enormous step forward.
I think it was a fairly well-known technique.
Signing digital data with hardware secure tokens is a commodity capability in the iPhone many of HNs users are reading this site with.
https://en.wikipedia.org/wiki/Content_Authenticity_Initiativ...
You’re probably right. This is easy, basic stuff that any recent college grad can do with their eyes closed.
We are quickly going to reach a point where any photo or video taken on a smartphone is inadmissible by default.
I get that there is a certain type of moron who thinks that the collapse in cost of misinformation has no harm... but all you've done is announce to the world that you are a moron.
It always comes down to provenance.
- the whole roll of negatives was prime evidence;
- police forces were one of the biggest users of Polaroid instant film.
And moreover, who had a darkroom and the skills to edit substantially a picture?
Whereas here we have nobodies being able to generate pixel-perfect fake "evidence" from the computers they already have.
https://www.metmuseum.org/exhibitions/objects/objects@exhibi...
The roll itself can be manipulated too. Most of the techniques used in modern photoshop are basically 1:1 carry overs of darkroom processes. Layers, dodge and burn, masking, etc.
There was a time you could take this class in highschool.
Have fun keeping making bad faith arguments alone.
What makes evidence "pixel perfect?" What digital photographs don't have to involve a chain of custody? Literally the first question the defense will ask is "how did you get this picture." If you say you pulled from a security system they can just go ask for the originals. This happens all the time.
Where people are getting confused is it's almost never _one_ piece of evidence that's used to convict you; although, it may be a single piece of evidence which convinces your attourney to railroad you into a plea deal.
https://rangefinderforum.com/threads/gentlemen%E2%80%93and-c...
How long did it take?
Now it’s a lot easier and faster
Surely it’s just a matter of time.
Meta, for one, is keen to bury such things and avoid responsibility for ad contents: https://www.abc.net.au/news/2026-04-17/andrew-forrest-battle...