Know the moment
your file was opened.
Starkive Certified (.ssz) is an encrypted delivery format that tracks opens and generates a signed PDF receipt — automatically.
Starkive is free on the Microsoft Store. Pro features from $2.99/mo.
The problem
You sent it. But did they open it?
Email attachments get ignored. Downloads happen silently. A ZIP file has no proof of anything. When you need to know your document was received and opened, a regular file is not enough.
No confirmation
You send a ZIP. It sits in their downloads folder. You have no idea if they ever opened it.
No paper trail
If a dispute happens, you have no proof of delivery. Just your word against theirs.
No security
Anyone who gets the file can open it. No password, no encryption, no control over who sees what.
Who uses it
Built for situations where “I think they got it” is not good enough.
Real scenarios where open tracking changes the outcome.
Sarah
Freelance Designer
“I send contracts before starting any project. With Starkive Certified I know exactly when my client opened it, so I know when to follow up.”
Marcus
HR Manager
“Offer letters are sensitive. I use .ssz so only the candidate can open it and I get a receipt the moment they do.”
James
Consultant
“I deliver final reports to clients. The PDF receipt gives me proof of delivery if there is ever a billing dispute.”
How it works
Three steps. No extra tools.
From your file to verified delivery in under a minute.
Create
Select your file in Starkive, choose Starkive Certified, set a passphrase. Your file is encrypted with AES-256 and packaged into a .ssz container.
Send
Share the .ssz file however you like — email, Google Drive, OneDrive, USB, anything. Send the passphrase separately.
Proof
The moment your recipient opens it in Starkive, you get an email notification and a signed PDF receipt with the timestamp.
A ZIP file is a container.
A .ssz file is a receipt.
For professionals who need more than hope.
Comparison
ZIP vs Starkive Certified
Same idea on the surface. Completely different in practice.
The one tradeoff: recipients need the free Starkive app on Windows to open .ssz files.
Under the hood
Technical specs
Built to be auditable, not just marketable.
Container format
Proprietary binary (.ssz) — not a ZIP variant
Encryption
AES-256-CBC with PBKDF2 key derivation
Passphrase
4-word EFF diceware wordlist (~51 bits entropy) or user-defined password
Open tracking
Encrypted ping to Starkive cloud on first open — no IP addresses stored
PDF receipt
Digitally signed, includes file name, timestamp, and recipient hint
Tamper detection
SHA-256 hash verified on open — modified files are rejected
Platform
Windows 10/11 (Starkive app required to open)
File types
Any file — PDFs, Word docs, images, spreadsheets, executables
SSZ file structure
Total header: 100 bytes · Payload: variable
Start sending files you can prove were opened.
Starkive Pro includes Starkive Certified, open notifications, PDF receipts, and cloud drive sync.
Starkive is free on the Microsoft Store. Pro features require a subscription at $2.99/mo.