A human-authorship certificate is only as trustworthy as the proof behind it. If the only evidence that a certificate is real is “look it up in our database,” then the certificate depends entirely on one company staying online, honest, and in business. That is a weak foundation for something meant to defend your reputation for years.
So ValidDraft manuscript certificates do not rely on trust. They rely on math. Each master certificate is signed with Ed25519, the same class of digital signature that protects SSH logins, software updates, and TLS connections across the internet. The result is a certificate that proves itself.
What is Ed25519, in plain English?
Ed25519 is a public-key signature scheme. ValidDraft holds a secret private key that never leaves our servers, and publishes a matching public keyfor the whole world. The two are mathematically linked, but you cannot work backwards from the public key to the private one.
Signing and verifying are two halves of the same lock:
- Sign: only the holder of the private key (ValidDraft) can produce a valid signature for a piece of data.
- Verify: anyone with the public key can check that a signature is valid, and that the data has not changed by even one character.
That asymmetry is the whole trick. We can prove we issued a certificate without ever revealing the secret that makes new certificates, and you can confirm it without asking us anything.
The public key lives here
ValidDraft publishes its issuer public key at validdraft.com/.well-known/validdraft-issuer.json. Fetch it once, and you can verify any master certificate we have ever issued, even offline.
What ValidDraft actually signs
A common worry is “does a 200,000-word novel produce a giant signature?” No. ValidDraft never signs the raw text. Each chapter you seal is hashed, and those chapter hashes are combined into a Merkle tree whose single root hash stands for the entire manuscript. ValidDraft signs a small, canonical record containing that root, so the signed record is the same compact size whether you wrote a novella or an epic.
{
"code": "M15X6E",
"merkle_root": "a3f1c9…", // root over every chapter hash
"chapters": 42,
"humanity_score": 87,
"issuer": "validdraft.com",
"signed_at": "2026-06-19T10:32:00Z",
"v": 1
}Because the Merkle root is part of the signed record, the signature also protects the text. Change a single word in any chapter and that chapter's hash changes completely, which changes the root, so the original signature no longer matches. Tampering becomes self-evident.
Why this beats a database lookup
A database row can be edited, deleted, or lost if a company shuts down. A signature is a permanent mathematical fact. Once issued, it keeps verifying for the life of the certificate, with or without ValidDraft in the loop.
Why manuscripts?
The Ed25519 seal is applied to manuscript master certificates on the Author plan. Here is the reasoning:
- A book is the high-stakes case. A manuscript is months of work, submitted to agents, publishers, and prize juries who may check it years from now, long after any single writing session. That is exactly the situation where proof needs to outlive the servers that issued it.
- One seal, every chapter. A manuscript is written across dozens of sessions. The Merkle root lets a single signature cover the whole work at once, and pin the chapters together in the order you wrote them.
- It is a lifetime guarantee. The signature does not expire and is never re-billed. Seal a manuscript once and the offline-verifiable proof is yours for good.
Article certificates work differently. They are verified with the same behavioral analysis and are publicly resolvable through validdraft.com and the content checker, but they do not carry an Ed25519 signature.
How to verify a certificate yourself
You never have to take our word for it. To independently verify a manuscript master certificate:
Open the master certificate and note its signed record and the signature value.
Fetch ValidDraft's public key once from /.well-known/validdraft-issuer.json.
Run a standard Ed25519 verification of the signature against the signed record using any crypto library.
If it passes, the certificate is authentic and unaltered. If any chapter was edited, it fails.
A note on the humanity score
ValidDraft's public certificate pages no longer display the numeric humanity score — only the verified/not-verified result — to keep the public trust signal simple and hard to misread out of context. The signed record above still lists the fields that back the Merkle-root tamper-evidence property described here; a self-verification path for the score specifically is being revisited to match. The tamper-evidence guarantee itself is unaffected.
That is the entire point of public-key cryptography: trust is replaced by a check anyone can run. Your master certificate does not ask people to believe ValidDraft. It hands them the tools to confirm it themselves.
A certificate worth trusting is one you do not have to trust. The math does the trusting for you.