Contact your intended conversation partner via some other authenticated channel, such as OpenPGP-signed email or over the phone. You should tell each other your fingerprints. (A fingerprint is a checksum that identifies an encryption key.) If the fingerprint matches, you should indicate in the dialog below that you have verified the fingerprint.
Nermes bab n udiwenni i d-teɛniḍ seg ubadu-nniḍen yettussetben  am yiznan yettuzemlen OpenPGP neɣ am tilifun. Ilaq ad temyinim idsilen-nwen umḍinen. (Adsil umḍin d taqrumma n yisenqaden i d-yebadun tasarut n uwgelhen.) Ma yella adsil umḍin yemṣada, ilaq-ak·am ad tesbegneḍ deg udiwenni ddaw, tesneqdeḍ adsil umḍin.