Plain English — promise
What is Ed25519?
It's the digital signature Omitly uses to prove a redacted document hasn't been altered since it was sealed — not by a single character. Here's what that means, with no maths and no jargon.
It's a signature a computer can check
Ed25519 is a way of signing things digitally. Like a handwritten signature, it says “this really came from me”. Unlike a handwritten signature, it can't be traced, copied, or forged.
It works with a pair of keys. The private key is like a personal stamp: it stays secret, and it is the only thing in the world that can make your signature. The public key is like a photograph of that stamp: anyone can use it to check a signature is real, but nobody can use it to make one.
Think of a wax seal
For centuries, a letter was sealed with wax pressed by a signet ring. The ring makes the seal; anyone who knows the pattern can recognise it. Ed25519 is that idea, made of mathematics — with one upgrade: this seal also breaks if anyone changes so much as a single letter inside the envelope.
How it works, in three steps
Two keys are made
Your copy of Omitly creates a matched pair of keys: a private key that never leaves your Mac, and a public key that can be shown to anyone.
The document is signed
When Omitly seals a redaction, the private key produces a signature — a short code that depends on every single character of the document.
Anyone can check it
Anyone with the public key can confirm the signature matches the document. If even one character changed after signing, the check fails. Loudly.
Why it matters
It can't be forged
Nobody can produce a valid signature without the private key — not with any computer available today. A signature that checks out really was made by the key holder.
It can't be quietly edited
Change anything in a signed document — one word, one number, one pixel — and the signature stops matching. Tampering isn't just difficult; it's visible.
Checking is free and safe
Verifying needs only the public key, which is public. You never share a secret, create an account, or trust someone's server to be told the truth.
It's boring, in the best way
Ed25519 is an open design, published in 2011, that anyone can inspect. It secures much of the internet's own plumbing — including SSH, the tool engineers use to log in to servers.
Where Omitly uses it
Sealing redaction reports
Every redaction produces a report of what was removed. Omitly signs it with your install's Ed25519 key and embeds the signed copy inside the redacted PDF itself — so the proof travels with the document and can't be quietly separated from it.
Signing licences
Omitly licence keys are Ed25519-signed too. The app checks a licence's signature against the public key it ships with, right on your machine — the same idea, pointed at a different document.
Quick questions
Is Ed25519 encryption?
No. Encryption hides information. A signature proves it. Ed25519 doesn't scramble your document — it lets anyone confirm the document is exactly what was signed, and that the right key signed it.
Why not just hash the file? What does a signature add?
A hash (a checksum) is a fingerprint of the file — and Omitly does compute one. But a hash alone only proves the file matches that hash, and anyone who edits the document can simply compute a fresh hash of their edited version and hand you that instead. A signature closes the loop: Omitly hashes the document, then signs the hash with the private key. Nobody can re-sign a tampered copy without that key — so the fingerprint itself becomes something you can trust, not just something you can compare.
What does the name mean?
“Ed” comes from the Edwards curve, the piece of mathematics it's built on, and 25519 comes from a prime number used in that curve. You don't need to remember either — the name is the least important part.
Who else uses Ed25519? Is it new?
It was published in 2011 and is now everywhere: SSH (how engineers log in to servers), the Signal protocol, Tor, parts of the internet's naming system, and several major blockchains. The US government approved it as a federal signature standard in 2023. The PDF standard itself added Ed25519 in 2022 — though most big-name PDF tools still sign with older algorithms, which is why Omitly's use of it is worth explaining rather than assuming.
Do I have to do anything?
No. Omitly makes the keys, signs the reports, and embeds the proof automatically. The only time you'll notice Ed25519 is when it catches a document that has been altered.
Redact with proof, not promises.
Every document Omitly redacts carries an Ed25519-signed report of exactly what was removed. On your Mac, never uploaded.