keybase allows users to "prove" a link between certain online identities (such as a twitter or reddit account) and their encryption keys. instead of using a system such as oauth, identities are proven by posting a signed statement as the account a user wishes to prove ownership of. this makes identity proofs publicly verifiable – instead of having to trust that the service is being truthful, a user can find and check the relevant proof statements themselves, and the keybase client does this automatically.