password, PIN, pattern, etc. • Something the user has:
SIM-card, OTP (one time password) generator, hardware token, etc. • A biometric property:
fingerprint, retina, voice, etc. • 2FA (2-Factor Authentication): • OTP by SMS or phone call • Hardware or software token • Push notifications in combination with PKI (public key infrastructure) and local authentication • Supplementary Authentication: • Geolocation • IP address • Time of the day • Device ID