A safety number is a short string derived from the public keys of both sides of an encrypted conversation, which the two people compare through a separate channel to confirm that no third party has interposed itself.
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Also called
Security code · Fingerprint verification
What Safety numbers means
End-to-end encryption guarantees that only the holders of the keys can read a conversation. It does not, on its own, guarantee that the keys belong to the person you think they do. If the service that distributes public keys hands you the wrong one, the encryption works perfectly and protects a conversation with an impostor. This is the machine-in-the-middle problem, and the only complete answer to it is verification outside the system.
Safety numbers make that verification possible without asking anybody to read a hexadecimal fingerprint aloud. Both sides compute the same number from the same inputs, so it can be compared over the phone, in person, or by scanning a code. If the numbers match, no substitution has occurred. If they differ, something has changed and the conversation should stop until it is explained.
A safety number changing is not automatically an attack — reinstalling an application or adding a device usually changes it too. What matters is that the change is surfaced rather than silently absorbed, so that a genuine substitution cannot be hidden among routine ones.
How Enclessa uses it
Enclessa computes a safety number for each end-to-end encrypted conversation and shows it to both sides, and it pins the other person’s user key on first contact. A key that changes afterwards blocks the conversation with a warning rather than quietly re-establishing it, which is the behaviour the architecture requires rather than an option an administrator can switch off.
Where Safety numbers is specified
Related terms
Read further
The security page explains how Enclessa protects data and which certifications it does not hold. The trust centre covers the processing agreement, the subprocessors and the residency position. The FAQ answers the questions buyers ask most often.
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