Okay, I can't explain it like you're 5... But here's as close as I can get. You've got DNA. Everyone's DNA is unique (shhh, just go with me for a minute). I

Okay, I can't explain it like you're 5... But here's as close as I can get. You've got DNA. Everyone's DNA is unique (shhh, just go with me for a minute). In fact, let's say that we found about 140 GATC pairs, which were also unique (we don't need your whole sequence, just those 140 pairs). Meaning, if we take your 140 GATC pairs, and we take my 140 GATC pairs, we'd be guaranteed to get different results. Now, if I want to refer uniquely to a person, I can just use those 140 GATC pairs, which looks roughly like QmXGTaGWTT1uUtfSb2sBAvArMEVLK4rQEcQg5bv7wwdzwU (when expressed with upper + lower + numbers). But, you've been thinking to yourself, WHAT ABOUT TWINS?!? Well, great question... ...but the cryptographic hash that we use is one where twins are EXCEEDINGLY UNLIKELY. Like, amazingly, shockingly, oh my god, unlikely. They exist, but in practice they're so uncommon that it doesn't matter. Maybe sometime, some unfortunate guy is going to request a picture of Natalie Portman, and get an MP3 of Ted Nugent. It could happen. It's just super unlikely to ever happen in practice. So, there you have it - a cryptographic hash is... excuse me, because this is a supremely flawed analogy... kind of like the DNA of a file.