# Proof of personhood

A **Proof of Personhood** is a set of data that guarantees the authenticity of an account. Typically, it should guarantee that the account is controlled by a human that does not control any other account. **Proof of Personhood** is often proposed to combat Sybil attacks by fake accounts, which may want to control a system through a 51% attack.

## Proof of Personhood on Tournesol

Tournesol uses **Proof of Personhood** to defend against the 51% attack.

Tournesol's main solution to **Proof of Personhood** is the validation of emails from a trusted email domain.

Tournesol is currently also looking into enabling accounts to vouch for other accounts. In particular, an account that is vouched by numerous certified accounts may become certified. In the long run, instead of a binary validation system, we consider using a Bayesian Proof of Personhood, which will assess the probability that an account is authentic. Such probabilities may then be turned into appropriate voting rights. However, determining how to do so is still a major research challenge.