Why does being able to load websites / browse internet depend on my computer’s clock being right?

Question

I notice that if I’ve traveled and my computer’s system clock is wrong by time zone, or I have not started up a computer in a long time (battery went dead) and its clock is wrong, that computer will not even be able to visit regular old websites on the internet (to look up information, what time it is, etc).

But if I reset the clock to approximately the correct time, things are back to normal. Why does it depend on this?

In: Technology

Answer 1

Suppose Alice and Bob came up with a secret language for talking to each other. As long as nobody figures out their secret language, everything is peachy, right? Not quite.

One day, Eve the Hacker sees Alice say something to Bob in their secret language, and then Bob says something back and hands Alice some money. A month later, the same thing happens. Eve has no idea what either of them said, but the next month, she records what Alice says to Bob. Then she waits another month, dresses up as Alice, walks up to Bob, and plays the recording.

To Bob, it sounds like his roommate “Alice” (who is actually Eve in disguise) is asking him for his half of this month’s rent. “Alice” is speaking the secret language, and nobody but Alice and himself should know it, so it must be Alice, right? So Bob hands her the rent money, and Eve runs off with it. The real Alice shows up a couple hours later, asks Bob for his half of the rent, and they both realize they’ve been scammed.

So they change the protocol: Now any time they start talking in the secret language, they say the current date first, also in the secret language. That way if Alice says “May 1, 2024. Could you please give me your half of this month’s rent?” and Eve records it and plays it back to Bob on June 1, Bob knows something’s not right. The downside is that now if Bob sets his watch wrong and he thinks it’s May 1, 2025 when it’s actually May 1, 2024, he’s going to think the real Alice is a scammer too.

In this analogy, Bob is your computer, Alice is the website, the rent money is your password/credit card info/etc., and Eve the Hacker is, well, a hacker. And the months are more like minutes or even seconds.