The One Date an AI Cannot Backdate - 中澤祐樹ブログ

日本語版: AI 時代の記事に残せる、たった一つの「書き換えられない日付」

Imagine you publish an article, and the next morning there is another one: paragraphs reordered, phrasing changed, a couple of names swapped, the skeleton identical, and dated after yours.

How would you show that yours came first?

If the same article shows up the next morning

Paraphrasing, restructuring, translating: these used to take human time, which put a natural ceiling on how much of your work could be lifted. Today you can hand a URL to a language model and ask for “a different article on the same topic”.

The web is already full of machine-written text, and of machines reading it:

Imperva’s 2025 Bad Bot Report found that 51% of web traffic in 2024 was automated, with malicious bots at 37%, up from 32% the year before. It is vendor data from Imperva’s own network, not the whole internet.
Cloudflare measured GPTBot requests growing 305% between May 2024 and May 2025 across its network, and later reported that about 80% of AI crawling over the previous year was for model training.
NewsGuard’s AI Tracking Center counted 49 news sites running AI-generated content with little human oversight in May 2023; by June 2026 the count was 3,749.
Ahrefs looked at 900,000 newly published pages in April 2025 and estimated that 74.2% contained some AI-generated content. Ahrefs itself notes that AI detectors are imperfect.

None of these numbers tells you the chance that your article gets copied, and I could not find a reliable survey of that. They do show that rewriting and republishing have become cheap. Detection is not a safety net either: a paper at NeurIPS 2023 showed that running AI-written text through a paraphrasing model dropped a detector’s accuracy from 70.3% to 4.6%.

What you can do after the fact is limited. Contact the other site, file a complaint with the search engine, or, if it matters enough, talk to a lawyer. Every one of those roads starts with the same question: “How do you show that yours came first?”

Every date you hold is editable

Your publish date is something you typed. WordPress’s own documentation explains how to change the publish date to a date in the past, and you can change the date of a post that is already live. The other site’s date is just as self-reported. Two people saying “I was first” does not settle anything.

The usual fallbacks have the same weakness:

The CMS date can be edited by whoever runs the CMS.
Photo metadata can be rewritten with free tools; ExifTool, for example, reads, writes and edits metadata, including shifting dates.
File timestamps change when a file is copied; on Windows a copy gets a new creation time.
A screenshot can be edited.
Third-party archives help, but you do not control whether or when they capture your page, and “right after publishing” is not guaranteed.

Each is better than nothing. None of them, on its own, answers “couldn’t you have made this up afterwards?”

What you need is for someone other than you to write down the date at the moment you publish, and to put that record somewhere nobody can rewrite later, including the person who wrote it down. The idea is old: Haber and Stornetta described time-stamping a digital document so that nobody, including the stamper, could backdate it, in the Journal of Cryptology in 1991.

What a third party can write down for you

That is what I built DateSealed to do. It is free, needs no account, and is operated by Lightscend Co., Ltd., my company in Japan.

You do not send DateSealed your article. You send its SHA-256 hash, a 64-character fingerprint that changes if a single character of the text changes. The hash is computed inside your browser, so the text itself never leaves your machine and is never stored by the service.

DateSealed then attaches two dates to that hash:

A signed time stamp in the standard RFC 3161 format, issued immediately by DateSealed’s own time-stamping authority. Such an authority signs the hash and the time; it does not need to know who asked.
A Bitcoin record. The hash is sent to public OpenTimestamps calendars and, within hours, is anchored in a Bitcoin block. From then on, anyone can check the date against the Bitcoin ledger alone, even if DateSealed shuts down.

The first one is only as trustworthy as I am. The second one is not mine to change. That is why both are there.

From the record page you can download the .tsr (the signed time stamp) and the .ots (the Bitcoin proof), along with the commands to verify them on your own machine. You do not have to trust DateSealed to check a DateSealed record.

What the record does not say

I want to be exact here, because the wrong expectation is how people get hurt.

A record shows that data matching this hash existed at the recorded time. That is all.

It does not show that a human wrote the text rather than a model.
It does not show that the content is accurate or original.
It does not show who made the record, or who holds the rights.
It does not guarantee legal effect. In Japan, the time stamps with an official status are those from providers accredited by the Minister of Internal Affairs and Communications. In the EU, a qualified electronic time stamp is presumed to be accurate about the date and time and the integrity of the data (eIDAS Regulation, Article 41(2), text as retained in UK law). A DateSealed record is neither of those. If you need one, use an accredited or qualified provider.

Still, “it existed at this time” is a useful place to start a conversation from. It will not settle one by itself. DateSealed gives you one more piece of evidence, cheap and quick, to put next to the rest.

Make it automatic: the WordPress plugin

A habit you have to remember will not survive a busy week. So there is a WordPress plugin.

Every time you publish or update a post, it computes the hash of the post text on your own server and sends only the hash. The text is not sent.
Because any edit changes the hash, every update gets a new record added, not a replacement. Your first publication is never overwritten, and the revision history accumulates somewhere you cannot reach.
It can show a small badge at the end of the post that links to the record page. The badge is optional.
It needs WordPress 5.8 or newer and PHP 8.2 or newer.

You can download it from datesealed.com/api. In the WordPress admin, open Plugins → Add New → Upload Plugin, choose the zip, activate it, then open Settings → DateSealed. A listing on wordpress.org is under review; once it is approved you will be able to install it from there too.

I think that “append, never replace” design fits the moment. Articles get edited for years after they go live. Having a dated trail of which version existed when, kept out of your own hands, is the part no model can fabricate afterwards.

Not only articles

The same mechanism works for anything you can hash.

Photos. Pick a file on the home page, or use Stamp photos, which records the original and makes a copy, in your browser, with a small badge showing the record date burned in. The photo itself is not uploaded. Keep the original; that is the file the record points to.
A URL you have already published. DateSealed fetches the public page once and records two hashes: the main text and the raw HTML. The fetched content is discarded as soon as it is hashed. The URL is stored but never shown on public pages.
The API. POST /api/v1/proofs with a hash. No authentication. Documentation is at datesealed.com/api.

Limits are 10 records an hour and 50 a day per IP address, and a URL counts as two.

A few habits that make the record worth having

Keep the original. DateSealed holds only hashes. Without the original text or file, the hash cannot be tied to anything.
Keep the proof files. Download the .tsr and .ots and store them with the original, so you can verify without DateSealed.
Record at publish time. The record’s time is the time you made it. Every day between publishing and recording is a day of evidence you gave away. That is the whole reason for the plugin.
Do not oversell it. It is evidence that something existed at a time. For a case that really matters, combine it with whatever formal registration or accredited time stamp your jurisdiction offers.

Try it

Open datesealed.com, paste a paragraph and press the button. It happens in your browser, nothing is uploaded, and the public pages set no cookies. It is available in 20 languages, with English as the default; the translations are machine-assisted, so tell me if a sentence reads wrong.

The background, including why I did not use an existing service, is in the launch post: DateSealed: A Free Way to Record When You Published Something, Without Uploading It.

AI took the effort out of copying. It did not give anyone the ability to write a time into the Bitcoin ledger after the fact. Dates are still the one thing worth having a stranger write down for you.