OpenTimestamps

OpenTimestamps Review Guide: Everything You Need to Know + FAQ

Ever wished you could prove you had a file at a specific point in time—without emailing it to a third party, paying a notary, or trusting a company to stay alive forever?

That’s exactly what OpenTimestamps offers: cryptographic proof of existence anchored to Bitcoin that anyone can verify—now or years from now—without relying on a middleman.

In this guide on Cryptolinks.com, I’ll show you what OpenTimestamps is, how it works, who it’s perfect for, and how to get started in minutes. We’ll also tackle the questions people ask most so you leave with zero guesswork.

The problem: proving time without trust, friction, or leaks

If you need to prove a document existed on a date—think IP protection, research, compliance, contracts, audits—the usual options are clunky, centralized, or privacy-unfriendly. Traditional digital timestamping (like the widely used RFC 3161 Time-Stamp Protocol) depends on trusted authorities whose keys and availability can change over time. If those authorities go away or their keys expire, you need extra evidence to keep your proof strong.

• Notaries and paper trails: slow, location-bound, and human-dependent.
• Centralized SaaS timestamping: convenient, but you’re trusting a company’s uptime, incentives, and policies—plus possible vendor lock-in.
• Upload-based tools: increase data exposure; once a file leaves your machine, you can’t un-send it.
• Key and service churn: traditional timestamp authorities can rotate keys or shut down, which can weaken long-term verifiability (see RFC 3161 and NIST SP 800-102 for how trust in authorities matters over time).

“I want proof this exact file existed at or before a time—without revealing it, trusting a company, or dealing with legal logistics every single time.”

That’s the bar. You want something future-proof, cheap (or free), private, and verifiable by anyone—ideally without relying on a single entity to vouch for you forever.

The promise: Bitcoin-backed timestamps you can verify forever

OpenTimestamps creates a proof of existence by committing a hash of your data into Bitcoin. Your file never leaves your machine; only its hash is used. Once the proof is anchored to Bitcoin, anyone can verify it using open tools—today or ten years from now—without asking permission from a company or server.

• Private by design: you never upload the file, only its hash.
• Neutral and open: open-source tools and a public standard.
• Nearly free: calendar servers batch thousands of hashes into one Bitcoin transaction.
• Long-term verifiability: the proof ultimately depends on Bitcoin’s globally observed history.
• Portable evidence: your tiny .ots proof travels with the file and can be checked by anyone.

Real-world snaps:

• Design/IP: timestamp your early sketches before sharing with a client to prove “I had this then.”
• Research: lock lab notes or datasets to a date without exposing the contents.
• Engineering: stamp release artifacts or build logs so you can prove integrity later.
• Finance/Compliance: timestamp policies, reports, or invoices to strengthen audit trails.
• Creative work: writers, photographers, and musicians can prove when a draft or track existed—no public posting required.

If you’ve ever hesitated to send a file to a service just to “get a timestamp,” this flips the model: keep the file, share only a hash, and use Bitcoin as your time anchor.

What I’ll cover in this review

Here’s what you can expect as you read on:

• What OpenTimestamps is (and isn’t), in plain English.
• How the trust model works and why Bitcoin is the anchor.
• How to stamp and verify files in minutes—no Bitcoin required.
• Where it shines: practical use cases for teams and individuals.
• Costs, speed, edge cases, and smart ways to use it in your workflow.
• FAQ that answers the biggest questions people ask on Google.

Curious how your file can be proven to exist at a time without ever leaving your computer? Let’s look at exactly what OpenTimestamps is and how it works—plain and simple.

What is OpenTimestamps and how it works (plain-English overview)

Simple definition

OpenTimestamps is a simple idea with powerful legs: it proves a specific piece of data existed at or before a certain time by committing a hash of that data into the Bitcoin blockchain. No accounts, no uploads, no middlemen who can change their story later. Just a small proof you can keep forever and show to anyone, anywhere.

Think of it like sealing your document in an envelope and getting a postmark from Bitcoin. The network doesn’t see what’s inside—only a fingerprint (the hash) that uniquely matches your content.

“Don’t trust. Verify.”

How it anchors to Bitcoin

Here’s the journey your file takes, in plain English:

• Hash locally: Your file is hashed on your own machine. Nothing leaves your device except that hash.
• Batching via calendars: Public “calendar” servers collect many hashes from many users and organize them in a Merkle tree (a compact way to bundle thousands of hashes).
• One on-chain commitment: The calendar makes a single Bitcoin transaction that commits the Merkle root (the tree’s fingerprint) to the blockchain.
• Your proof path: You receive a small proof file that shows the path from your file’s hash up to that Merkle root. Anyone can later verify that path against the Bitcoin blockchain.

Real-world snapshots make this click:

• Software release: You timestamp the SHA-256 of your “v1.4.2” build. Months later, anyone can verify the binary you shipped is exactly the one that existed before your public launch.
• Research notes: You timestamp a ZIP of your lab notebook. If a new paper drops, you can prove your notes existed before it—without revealing your private data.
• Photography RAWs: You timestamp a folder of RAWs before sending edited proofs to a client. If someone questions authorship or timing, you’ve got a cryptographic paper trail.

Under the hood this is standard, battle-tested cryptography: hashing for integrity (see NIST guidance on hash algorithms in SP 800-107) and Merkle proofs that compress many items into one commitment.

Calendars and the trust model

Calendars are convenience, not a long-term trust anchor. They’re just aggregators that help everyone share one low-cost Bitcoin transaction. Once your proof includes the data anchored on-chain, verification becomes trustless—you can check it yourself against Bitcoin using your own tools.

Key points:

• No ongoing reliance: After the Bitcoin transaction confirms and your proof is upgraded with the full path, you don’t need calendars to verify.
• Redundancy-friendly: You can use multiple calendars. If one disappears tomorrow, your existing proofs remain valid because the source of truth is Bitcoin.
• Self-sovereign verification: You can point verification at your own Bitcoin node, Electrum, or other infrastructure—no single chokepoint.

It’s a smart handoff of trust: short-term help from calendars, long-term guarantees from Bitcoin.

What OpenTimestamps isn’t

Knowing what a tool doesn’t try to do is just as important:

• Not a blockchain: It uses Bitcoin for anchoring; it isn’t its own chain.
• Not file storage: It never stores your documents. Keep your files safe—that’s on you.
• Not identity or notarization of content: It proves existence at a time for a specific hash, not who created it or what’s inside. If you need authorship, pair it with digital signatures (e.g., sign then timestamp).
• Not DRM or copyright registry: It won’t police usage; it simply gives you ironclad “I had this then” evidence.

If you’ve used traditional timestamp authorities (e.g., RFC 3161 servers), think of OpenTimestamps as the same core goal—proving time—but without needing a central authority. Bitcoin becomes the impartial witness.

Why Bitcoin

Time anchors are only as strong as the ledger behind them. Bitcoin has a few properties that make it exceptional for this job:

• Security-through-observation: It’s the most widely watched and independently verified chain, which makes tampering astronomically difficult.
• Proof-of-work finality: Confirmations accrue economic weight. The deeper the block, the tougher it is to rewrite history.
• Neutral and durable: Open, permissionless, and battle-tested for over a decade. Your proof shouldn’t depend on a startup’s survival or a vendor’s pricing.
• Efficient commitment: Merkle trees let thousands of timestamps share a single, low-fee on-chain commitment.

Or as a friend put it: “If you’re going to etch a moment in stone, pick the biggest stone.”

Ready to see this in action on your own machine—no Bitcoin required, no file uploads, just a one-line command? Up next, I’ll show you exactly how to stamp and verify a file in under five minutes, step by step.

Getting started fast: stamp and verify in under 5 minutes

Install the CLI (60 seconds)

Here’s the quickest way to run OpenTimestamps locally. It won’t upload your file; it only hashes it on your machine.

• macOS / Linux / Windows (via Python): install the official client with pip.

pip install opentimestamps-client
ots --version

If “pip” isn’t found, install the latest Python first. That’s it — you now have the ots command.

Tip: Prefer a portable setup? Use a virtual environment and install opentimestamps-client inside it.

Stamp a file (instant receipt, auto-upgrade later)

Let’s create a timestamp for something real — say an NDA, a product design, or a build artifact. I’ll stamp a PDF:

ots stamp nda-v3.pdf

You’ll immediately get a small sidecar file: nda-v3.pdf.ots. That’s your proof. It’s “pending” right away (already useful), and becomes “final” once the Bitcoin transaction that includes your data’s hash confirms.

• Multiple files at once: stamp an entire folder of assets, logs, or releases in one go.

ots stamp *.pdf
ots stamp dist/*.tar.gz

Want the proof to include the full on-chain path once it’s ready? Just run an upgrade later (or during verification):

ots upgrade nda-v3.pdf.ots

Real-world example: I time‑lock my release notes and the final binary for a public build. If anyone questions when I published, the proof answers for me — no debate, no gatekeepers.

“Don’t trust, verify.” — the Bitcoin mantra for a reason

Verify a file (your node, Electrum, or public infra)

Verification is the whole point — proving the timestamp against Bitcoin, anytime.

ots verify nda-v3.pdf.ots

You’ll see either a pending status (not yet anchored) or a confirmed, on‑chain timestamp with block height and date. If you want to control the data source:

• Your own Bitcoin node: configure the client to talk to your node’s RPC for maximum independence.
• Electrum: point the client to your Electrum server if you prefer that setup.
• Public infrastructure: the default works fine for quick checks.

When verifying, the client can also fetch missing pieces and upgrade your proof so you keep a fully self-contained file going forward.

Proof lifecycle (what actually happens behind the scenes)

• Now: you get a partial proof instantly. That’s a cryptographic receipt showing your file’s hash is committed to a calendar and on its way to Bitcoin.
• Soon: once the calendar’s batch hits Bitcoin and confirms, your proof becomes fully anchored.
• Upgrade: run ots upgrade (or verify) to embed the complete path so your .ots file stands on its own.
• Confidence: after a few confirmations, it’s extremely robust. For higher assurance (e.g., audits), wait 6+ confirmations like you would for high-value Bitcoin transactions.

Why the two-step feel? Calendars batch many users’ hashes into one Merkle root to keep on-chain fees near zero for everyone, which is why stamping is typically free.

File types and size (anything you can hash)

Stamp a photo, a CAD file, a log archive, a zip of your research — anything. Only the hash is used, not the content, so size isn’t a practical limit beyond the time it takes to hash.

• Speed reality: modern CPUs hash hundreds of MB/s; a 1 GB file often hashes in a couple of seconds.
• Security confidence: SHA‑256 collision resistance is widely recommended by NIST for digital integrity. See FIPS 180‑4.
• Best practice: store the .ots next to the original file, in your repo, or inside your release bundle so it’s always traveled together.
• Size of proofs: .ots files are tiny (usually a few KB), perfect for backups and long-term archiving.

Example workflow: stamp a zipped folder of your models before sending to a client; later, both sides can verify the exact archive existed “then,” even if the delivery happened days or weeks after.

That’s the quick start. But what about the sensitive stuff: does any server learn your content, and what if those servers go down? The next section answers the trust questions that matter most — ready to see how the privacy and reliability actually hold up?

Security, privacy, and reliability: the real trust model

Privacy by default

Your file never leaves your machine. OpenTimestamps (OTS) only uses a hash of your data, created locally. That hash is a one-way fingerprint—fast to compute, practically impossible to reverse. Calendars only see hashes, not content, filenames, or metadata.

In plain terms: if I timestamp a confidential 200-page contract, the calendar learns nothing about the contract. It just receives a random-looking string—no names, no clauses, no amounts.

“We have proposed a system for electronic transactions without relying on trust.” — Satoshi Nakamoto

That said, good privacy is a habit:

• Hash locally, always. OTS tools do this by default.
• Consider entropy. If you timestamp a very short or common string (like a simple password), a determined adversary could guess it and match the hash. For tiny secrets, add randomness (e.g., zip with a random filler file) before stamping.
• Hide network metadata when needed. If your hash is sensitive, use Tor or a VPN so calendars don’t see your IP.
• Be careful where you publish the hash. Sharing the hash publicly links the hash to you. If that’s a problem, keep it private and only reveal it when you need to prove time.

Real-world example: a journalist timestamps a draft of an investigation. The calendar learns only the hash, not the topic or sources. Months later, if questioned, that hash can be checked against Bitcoin to prove the draft existed back then—without exposing anything today.

Verification is independent

Once your proof is anchored to Bitcoin, you don’t need any OTS server to verify it. Your proof contains the data needed to:

• Re-hash your file locally
• Walk the Merkle path to the transaction’s commitment
• Check that the transaction is in a Bitcoin block
• Confirm that block sits on the chain you accept as valid

You can verify using your own Bitcoin Core node, Electrum, or any trustworthy infrastructure you control. No account, no login, no cloud dependency. If you’re serious about long-term proofs, running your own node is the gold standard.

What if calendars go down?

Calendars are helpful, not authoritative. They batch many hashes into a Merkle tree and anchor the root to Bitcoin. After that anchor is on-chain and your proof has been upgraded to include all necessary data, Bitcoin is the source of truth. Even if every public calendar disappeared tomorrow, your anchored proofs remain valid and verifiable.

Resilience tips I use:

• Stamp with multiple calendars. Redundancy costs nothing and avoids a single point of failure.
• Archive your .ots files. Keep the upgraded proof; it contains everything you need later.
• Optionally run your own calendar. For strict compliance or regulated environments, self-host a calendar so your organization controls anchoring schedules and policies. See the OpenTimestamps GitHub.

I’ve seen teams keep stamping through brief public-calendar outages without missing a beat. When the Bitcoin transaction confirms, the final proof is independent of those servers.

Edge cases and limits

Time anchoring is bound by Bitcoin’s rules, and that’s a feature. A few realities to keep in mind:

• You wait for confirmations. An immediate “pending” proof is useful, but strong assurances come after on-chain confirmations. The classic guideline is 6 confirmations for high assurance, which statistics from the Bitcoin whitepaper suggest makes reorg risk vanishingly small for honest-majority assumptions (Nakamoto, 2008).
• Reorgs happen, but they’re usually shallow. One-block reorgs occur occasionally; two-block reorgs are rare; deeper reorgs on mainnet are extremely rare in practice (see historical notes by BitMEX Research). Waiting a few confirmations handles this risk.
• Fee spikes can slow inclusion. During congestion (e.g., the 2023 BRC-20 mania), fees surged and some anchors took longer to confirm. Calendars batch many users together to keep costs low, but their transactions still compete for block space. Your pending proof still exists and will upgrade as soon as the transaction is mined. If timing is critical, consider running a calendar and choosing higher fees.
• Time is “at or before,” not an exact second. A block’s timestamp and height give you a clear “no later than” bound. Resolution is typically minutes, which is more than enough for IP protection, audit trails, and compliance records.

Example: a medical device company timestamps testing logs daily. Even if fees are high one afternoon, the logs anchor later that day. With 6 confirmations, auditors get strong, chain-backed assurance those logs existed before a specific time.

Integrity vs. authenticity

OTS proves that a specific hash existed by a point in time. It does not say who created the file or what the file means. That’s the difference between integrity (unchanged data) and authenticity (who authored it).

If you need authorship or intent, add signatures:

• Sign, then timestamp. Use PGP/GPG, Minisign, Sigstore, or a code-signing certificate to sign the file. Then timestamp both the file and the signature. Now you can prove “this person signed this exact content, no later than this time.”
• Make your public key discoverable. Publish it on your website, GitHub, or DNS (with DNSSEC). That links signatures to a visible identity.
• For teams, standardize the ritual. Example: CI signs release artifacts, then timestamps the artifact and the .sig file. Every auditor gets an end-to-end chain of evidence.

Picture a designer sharing early CAD files with a manufacturer. A timestamp proves the design existed; a signature ties it to the designer. If there’s a dispute, both the “when” and the “who” are covered.

So who actually benefits the most from this, and what are the smartest ways to weave timestamps into everyday work—research, releases, contracts, audits—without adding friction? Keep going; I’m about to show the playbooks people use and the alternatives worth considering next.

Use cases, who it’s for, and alternatives

“Memory is cheap. Proof is priceless.”

Who gets the most value

Anytime you need to show “I had this then” without exposing the contents, OpenTimestamps becomes your quiet superpower. I see the biggest wins for:

• Researchers and academics — lock preprints, datasets, lab notes, and protocols in time to support reproducibility and priority claims.
• Creators and founders — protect concepts, drafts, designs, tracks, and scripts as evidence of prior art without leaking ideas.
• Dev and security teams — timestamp build artifacts, SBOMs, release packages, and logs to harden your software supply chain.
• Compliance and audit — add verifiable time anchors to policy docs, risk registers, and audit evidence for frameworks like ISO 27001 or SOC 2.
• Legal and investigations — prove when a document, image, or archive existed; pair with signatures when you need identity or intent.
• Finance and ops — seal invoices, contracts, and price quotes to reduce disputes and “he said, she said” moments later.

Practical examples

Here’s how people actually put it to work—no buzzwords, just outcomes that matter:

• Research notes and preprints: Save a hash of your lab notebook PDF or Markdown bundle today; verify it years later when your paper hits peer review. A well-known survey by Nature highlighted reproducibility concerns across science—timestamping your data and analyses helps show a clean, time-ordered provenance.
• Design drafts and product IP: Export a daily ZIP of CAD files or UX mocks, timestamp it, and store the .ots proof alongside. If a competitor claims prior ownership, you have cryptographic, third‑party‑independent evidence of existence.
• Software releases: Hash your release tarball (or container image digest), timestamp the hash, and publish the .ots file with your release notes. Users can verify exactly what you shipped and when—great for trust in open source.
• Build pipelines: After producing a build, timestamp the artifact and the SBOM. If you’re following the SLSA framework, this adds a simple, Bitcoin-backed time anchor to your provenance story.
• Security logs and forensics: Roll logs hourly into chunks, record a Merkle root, and timestamp that root. Even if the SIEM changes or you rotate vendors, your historical logs keep a tamper-evident timeline.
• Contracts and invoices: Hash PDFs before sending, timestamp the hash, and stash the .ots proof. In any future dispute about timing, you can show the exact document existed at or before the claimed date—without revealing contents to anyone today.
• Media and creative works: Writers, musicians, photographers—timestamp drafts or source files as you go. If you ever need to show an idea’s lineage, you’ve got a neutral, permanent anchor.

Team workflows that actually stick

Timestamps shine when they’re automated and boring—in a good way. A few patterns I recommend:

• CI/CD integration: After your build step, hash the artifact, run an ots stamp, and upload the .ots proof as a build artifact. When the Bitcoin transaction confirms, re-run a short “upgrade proofs” task to embed the final data.
• Release checklists: Treat the .ots proof like a checksum file. Publish it next to your binaries so users and auditors can pick it up later.
• Git workflows: For high‑stakes repos, have a release hook that timestamps the tag, release notes, and artifact digests. It’s cleaner than trying to timestamp every single commit.
• Log hygiene: Periodically compute a Merkle root of log segments (or daily archives) and timestamp just the root. You get compact proofs that scale even with huge log volumes.
• Design sprints: At the end of each sprint, bundle the sprint deliverables and timestamp once. It gives product, legal, and leadership a shared, verifiable heartbeat.

Alternatives and comparisons

You’ve got options. Here’s how they stack up in the real world:

• Centralized timestamp authorities (RFC 3161) — Think traditional CAs offering TSA endpoints. Pros: established PKI, easy enterprise fit. Cons: you trust the issuer, there are fees, and long‑term resilience depends on that authority’s records and policies.
• Notarization and e‑signature suites — Platforms like document signing tools give you convenience and workflow. Pros: polished UX, identity workflows. Cons: vendor lock‑in, recurring costs, and often content exposure to the provider; timestamps reflect their system of record.
• Ethereum or multi‑chain stampers — Some services anchor to Ethereum or several chains. Pros: programmability and optional smart contract logic. Cons: varying security models, fee volatility, and a wider surface area for future compatibility. Decide based on your threat model and how you plan to verify in 10+ years.
• Other Bitcoin timestamp services — Providers like Woleet and OriginStamp offer APIs, dashboards, and features such as identity signatures or multi‑chain anchoring. Pros: enterprise tooling and support. Cons: pricing, account requirements, and potential data-sharing trade‑offs depending on configuration.

OpenTimestamps stands out for being open-source, nearly free, private by design, and neutral: you keep your data local, rely on Bitcoin for finality, and avoid platform lock‑in. If you ever need identity on top, pair OTS with digital signatures (PGP, code signing, or corporate PKI) and you get the best of both worlds—proof of existence plus proof of authorship.

Curious about what this costs in practice, how fast “final” feels on a busy day, and the slickest ways to wire it into CI without slowing builds? I’ll show you the neat tricks and exact expectations next—want the one‑liner I use in production?

Costs, performance, advanced tips, and tools

Let’s talk real-world: what it costs, how fast it feels, and the pro moves that make OpenTimestamps hum in production. This is where you turn “nice idea” into a resilient, low‑friction habit across your files, builds, and teams.

Costs: how “almost free” actually works

Stamping is usually free for end users because calendar servers batch thousands of hashes into a single Bitcoin transaction. That single on-chain fee gets amortized across everyone stamped in that batch.

If you’re curious about the economics or plan to run your own calendar, here’s the simple model:

• Calendar batching: One OP_RETURN transaction (often ~200–300 vbytes) includes a Merkle root that covers many user hashes.
• Fee math: Cost ≈ transaction_size_vbytes × fee_rate_sat/vB. For example, 250 vB at 15 sat/vB ≈ 3,750 sats. If 10,000 hashes ride that same tx, the per-hash cost is effectively ~0.375 sat. That’s fractions of a fraction of a cent at most BTC/USD rates.
• Who pays? Public calendars cover the miner fee for the batch. Many accept donations; if you rely on them heavily, it’s good etiquette to give back.
• Running your own calendar: You’ll pay the on-chain fees yourself.

  • Batch interval policy (e.g., every N minutes or when X hashes accumulate) is your main lever.
  • In fee spikes, you can wait for cheaper periods or pay for faster confirmations.

Practical takeaways:

• For most users and teams, stamping is functionally free and scales to thousands of files with no budget surprises.
• If you need SLAs or internal controls, run a calendar and set a batch policy. You’re still paying per transaction, not per file.

Speed and finality: what to expect in real life

Right away you’ll have a pending proof. It’s useful because it builds the chain of evidence immediately. Once the batch hits Bitcoin and confirms, your proof “hardens.”

• Typical timing: Bitcoin blocks arrive ~every 10 minutes on average (see Satoshi’s original design in the Bitcoin whitepaper). Expect 1–3 blocks (10–30 minutes) for a strong anchor in normal network conditions.
• Peak congestion: If fees spike, calendars might delay anchoring until it’s economically sensible, or they’ll pay up to confirm faster. Either way, your pending proof already exists and will upgrade automatically.
• Finality comfort levels:

  • 1 confirmation: Good enough for many workflows.
  • 3 confirmations: Commonly considered very safe.
  • 6 confirmations: Industry standard for near‑zero reorg risk; the probability of reversal drops exponentially with each block (again, per the whitepaper’s analysis).

“Time in Bitcoin is probabilistic, but its certainty hardens with each block.” Treat confirmations like security dials: turn them up for what matters most.

Advanced setups that pros use

If you want more robustness, privacy control, or automation, here are patterns I’ve seen work across teams and long-lived archives.

• Verify against your own infrastructure:

  • Point verification to Bitcoin Core (your own node) for maximum independence.
  • Or use Electrum as a lightweight backend. This keeps verification fast and reduces reliance on public servers.

• Use multiple calendars for redundancy:

  • Stamp with more than one calendar URL. If one disappears, you still have parallel anchors and upgrade paths.
  • This costs you nothing extra as a user and buys operational resilience.

• Archive and upgrade your proofs:

  • Store the .ots file right next to the original artifact (e.g., document.pdf and document.pdf.ots).
  • After confirmations, run an upgrade to embed the full chain data into your proof so it stays self-contained for future verification.
  • Back up proofs somewhere boring and durable: object storage, offsite drive, or a “compliance” repo.

• CI/CD stamping that feels invisible:

  • At the end of your build, timestamp your release artifact (e.g., build.tar.gz) and commit the .ots file as a release asset.
  • Have a scheduled job (every 10–20 minutes) upgrade recent proofs so releases quickly become “final.”
  • Pair with reproducible builds for a strong “we built this exact thing at this exact time” story.

• Manifest trick for huge file sets:

  • Hash each file (e.g., SHA‑256) and write a manifest file with filenames + hashes.
  • Timestamp the single manifest. Now you have one proof that locks the entire set to time.
  • Later, you can prove any file in the set by showing its hash matches the manifest entry that was timestamped.
  • Bonus: rotate manifests daily/weekly to keep them small and searchable.

• Offline-first paranoia with clean boundaries:

  • Hash sensitive files on an offline machine (keep the files air‑gapped).
  • Move only the hashes to an online box and include them in a manifest you timestamp.
  • When you need to demonstrate provenance, recompute hashes offline and match them to the timestamped manifest.

• Run a private calendar for compliance:

  • Great for regulated teams that want guaranteed schedules and audit logs.
  • Set batch cadence (e.g., every 5 minutes), monitor mempool conditions, and push anchors on policy.
  • Keep clean logs: received hash count, batch times, and txids—helps during audits.

Helpful links and tools

• Official site: opentimestamps.org
• Code and issues: GitHub: opentimestamps
• Bitcoin node: Bitcoin Core
• Lightweight client: Electrum
• Background reading: Bitcoin whitepaper (on probabilistic finality)

Want to know if you need to hold BTC, what happens if calendars vanish, or how this holds up in court? I’ve got the exact answers you’re looking for—keep going for the FAQ next.

OpenTimestamps FAQ and wrap‑up

Is OpenTimestamps a blockchain?

No. It’s a protocol and a set of open tools that anchor your data’s hash into Bitcoin. Think of it as a lightweight “proof-of-existence” layer that piggybacks on Bitcoin’s permanence. Your file’s hash is batched with many others, rolled up into a Merkle root, and that root is committed on-chain. The blockchain part is Bitcoin; OpenTimestamps is the bridge from your data to that anchor.

Do I need to hold or spend Bitcoin to use it?

No. Public calendar servers batch many users’ hashes into a single Bitcoin transaction and pay the fee. You can stamp and verify without ever buying BTC. If you want maximum control, you can run your own calendar and fund it, but that’s optional and typically only needed for strict internal policies or high-volume setups.

Does OpenTimestamps see or store my files?

No file uploads. Ever. Your file stays local; only its cryptographic hash is used. That hash is a one-way fingerprint—practically impossible to reverse back into the original content. Calendars see batched hashes, not your documents, designs, or code. This is the main reason creative teams and compliance folks are comfortable stamping sensitive material.

What happens if calendars disappear?

Your proofs don’t break. Once your proof is anchored to Bitcoin and you’ve upgraded it to a “final” state, it can be verified independently with any Bitcoin source (your own node, Electrum, or public infrastructure). You can also use multiple calendars to get redundancy while you wait for confirmation. Even if every calendar went offline tomorrow, the proofs already anchored remain valid because Bitcoin is the source of truth.

Quick tip: keep the .ots file alongside the original artifact. If a proof is still “pending,” you can upgrade it later when a calendar or your own node is available again.

Is this legally useful?

Yes, as technical evidence of existence at or before a time. OpenTimestamps provides verifiable, cryptographic proof that “this exact hash existed by block X.” Courts routinely admit digital evidence when the process is explained by a qualified witness. In the U.S., FRE 901 covers authentication via a reliable process. In the EU, electronic timestamps are recognized under eIDAS (Article 41 addresses qualified electronic time stamps). Different jurisdictions apply different standards, but cryptographic hashes and timestamping are widely understood.

Important: OTS proves existence and integrity, not identity or intent. If you need to show who authored or approved something, pair OTS with a digital signature (PGP, X.509, or a corporate code-signing setup). This isn’t legal advice—talk to counsel for your specific use case.

Real-world snapshot: I’ve seen teams timestamp product requirement docs and then sign the final PDF with a company cert. In disputes over “who had what, when,” the OTS proof plus the signature chain cut through the noise fast.

How long does a “final” proof take?

Instant partial, then final after confirmations. You get a pending proof right away (useful for “I started the process now”). Once the batch hits the Bitcoin chain and gets confirmations, your proof upgrades to a strong, final state. In normal conditions, that’s usually within an hour. During fee spikes or congested mempools, it can take longer. You can check and upgrade your proof later to embed the full path to the anchoring transaction.

Example: I stamped a design mockup at 10:05. The calendar batched it and anchored by ~10:30. By ~10:55 (after a few confirmations), I upgraded and had a final proof tied to a specific block. Months later, verification still passes in a few seconds.

Key takeaway: OpenTimestamps gives you a portable, Bitcoin-backed receipt for your data—cheap, private, and easy to verify long after today’s services come and go.

Conclusion: my take

OpenTimestamps hits the sweet spot. It’s open, nearly free, private by design, and piggybacks on Bitcoin’s security. For proving “I had this then,” it’s hard to beat. If you care about future-proof, neutral evidence—without trusting a middleman—add OTS to your workflow. Stamp releases, proposals, research notes, and contract drafts. Keep the .ots files with your artifacts. Pair with digital signatures when identity matters. That’s a simple recipe that scales from solo creators to regulated teams.

If you want to explore further, start at opentimestamps.org and the GitHub repos linked there. It takes minutes to set up, and the peace of mind lasts for years.