What tamper-proof would claim
Tamper-proof would mean the file cannot be altered. A recipient can always save a PDF, edit a copy, or rename it. Nothing about sealing freezes the bytes on someone else’s device. Using tamper-proof for that would overclaim.
What tamper-evident means
Tamper-evident means a change is detectable when the recipient checks the seal. Opcilo stores a fingerprint of the sealed file. The check compares the file in hand to that fingerprint. A mismatch means this is not the sealed file. The evidence is the result of that check.
Opcilo’s wording, and the wording we do not use:
| Topic | Opcilo | Other |
|---|---|---|
| The claim | Tamper-evident: a change is detectable when the recipient checks the seal | Tamper-proof: the file cannot be altered |
| If someone edits a copy | The check reports it is not the sealed file | The edited copy still exists; the original bytes were not frozen |
- 1
The file is sealed
Safe pathOpcilo keeps a fingerprint of those bytes.
- 2
Someone edits a copy
Risk pointThe file on their device can change. Tamper-proof would deny this.
- 3
The recipient checks the seal
Safe pathNo account. The check compares the file in hand to the fingerprint.
- 4
The change is evident
Safe pathA mismatch means this is not the sealed file.
The file can be edited. The seal makes that edit evident when someone checks.
The check still has to happen
Tamper-evident does not mean an unchecked attachment announces itself. The evidence appears when someone opens the verification link and checks the file. Until that check, a swapped PDF can look ordinary.
That check is the sealing loop in what document sealing is.
Frequently asked questions
Why not say tamper-proof?
Tamper-proof would claim the file cannot be altered. A copy can still be edited. Tamper-evident is accurate: the change is detectable when the recipient checks the seal.
Does the file announce that it was changed?
No. The evidence appears when the recipient checks the seal. An attachment that nobody checks can still look ordinary.
What does a mismatch mean?
The file in hand is not the sealed file. The seal does not repair the copy. It makes the difference evident.