&gt; Theoretically, attackers can send malicious NTP requests to adjust every iPhone&#x27;s time settings to January 1, 1970<p>Just to be clear, this (typically) isn&#x27;t possible. NTPD refuses to adjust the clock if the time difference is too large. (I don&#x27;t recall what the default threshold is, but IIRC it&#x27;s less than 24 hours, certainly less than 46 years.)<p>This is important for TLS - if an attacker could significantly roll back your system clock, they could trick your browser into accepting an expired certificate. Compromised certificates would be a problem forever, rather than just until they expired.