Privacy Policy
Last updated: August 23, 2026
Proof Stamp ("the Service") treats the appropriate handling of users' personal information as an important responsibility, and sets out this Privacy Policy ("this Policy") accordingly.
This English translation is provided for convenience only. Where any discrepancy exists between this translation and the Japanese original, the Japanese original governs.
1. Information We Collect
The Service collects the following information in the course of providing the Service.
| Type of information | Details |
|---|---|
| Account information | Email address (the Service does not use passwords and does not collect or store one) |
| Uploaded data | The uploaded file itself, its filename, size, type, and SHA-256 hash value |
| Payment information | Subscription status and a customer ID issued by our payment processor (Stripe, Inc.). Card numbers and other payment details are never stored on the Service's own servers |
| Access information | Login timestamps, authentication tokens, and records of login links issued/sent (emailed to you, expiring in 15 minutes, single use) |
2. Purpose of Use
- Providing the Service (creating, storing, and issuing certificates for file timestamp proofs)
- Account authentication and prevention of impersonation or fraudulent use
- Managing storage and features according to your plan, and billing
- Responding to inquiries
- Improving the Service and investigating/resolving issues
3. Disclosure to Third Parties / Subcontracting
The Service entrusts data handling to the following external providers.
- Cloudflare, Inc. — Used as our server, database, and file storage infrastructure. All uploaded files and account information are stored on Cloudflare's infrastructure.
- Stripe, Inc. — Handles payment processing (subscription billing). Card numbers and other payment details are managed by Stripe; the Service does not retain them.
- OpenTimestamps calendar servers (opentimestamps.org, eternitywall.com, catallaxy.com) — Only the SHA-256 hash value of an uploaded file is sent to these servers, used to build the timestamp proof on the Bitcoin blockchain. The file itself is never transmitted externally.
Except as described above, or as required by law, we do not disclose personal information to third parties without your consent.
4. Data Retention and Deletion
You may delete any uploaded file yourself, at any time, from your account page. If you wish to delete your account, please contact us at the support address below. Data is promptly deleted after such a request, except where retention is required by law.
5. Use of Cookies, Etc.
The Service does not use cookies for advertising or third-party analytics. To keep you signed in, an authentication token is stored in your browser's localStorage; this is used solely to provide the Service's functionality and for no other purpose.
6. Data Security
The Service does not use passwords. Instead, it uses a magic-link authentication method where a login link (expiring in 15 minutes, single use) is emailed to you. All communication is encrypted via HTTPS. Sending of login links is rate-limited per email address and per IP address to prevent abuse.
7. Requests for Disclosure, Correction, or Deletion
If you wish to request disclosure, correction, or deletion of your own information, please contact us at the support address below. After verifying your identity, we will respond promptly in accordance with applicable law.
8. Contact
For inquiries about the Service's operator or the handling of personal information, please
contact us at:
Operator: Proof Stamp (Person in charge: Takuya Enomoto)
Email: ca200mg@gmail.com
9. Changes to This Policy
This Policy may be revised without notice due to changes in law or in the Service. Where a material change occurs, we will announce it clearly on the Service.