# Known Identifiers

The Known Identifiers tool can be a simple and very powerful way to confirm that a person is only using one BrightID account.

It relies on an Aura Player knowing which identifiers (such as social accounts, legal names, addresses, phone numbers) are associated with a person. This knowledge comes from an existing relationship with that person, since [Aura Players should not ask subjects for personally identifying information](../../intro/how-aura-works#privacy).

Using a [Socialist Millionaire Protocol](https://en.wikipedia.org/wiki/Socialist_millionaire_problem#Off-the-Record_Messaging_protocol), Aura Players can agree on the same BrightID account without revealing any new private information to each other.

[See the BrightID forum post on known identifiers for a full description.](https://forum.brightid.org/t/fighting-small-scale-sybil-attacks-with-known-identifiers/503)

{% embed url="https://forum.brightid.org/t/fighting-small-scale-sybil-attacks-with-known-identifiers/503" %}
