Encryption is the science that enables digital items to be protected by a password. Standard encryption works well when only one person needs access to whatever is password protected. When multiple people need access to encrypted information, because sharing passwords is unsafe, a different type of encryption is needed. This type of encryption is called asymmetric encryption.
Asymmetric encryption works like a mailbox locked with a key. Anyone can deposit mail into the mailbox, but to get mail out, a key is required. Digitally, the mailbox is referred to as a “public key” and the key required to unlock it is the “private key”. These two keys are mathematically linked so that any information sent to a public key can always be unlocked with its unique private key.
Asymmetric encryption is one of the properties which makes cryptocurrencies the world’s most secure way to transact. It is what allows any user to have a shareable public key and address to which anyone can send funds and also a private key making the user the only one able to spend these funds.
To demonstrate how this works, let’s imagine that I live in California and my mother, father, and sister all live in North Carolina. Father’s day is coming up and I want to buy my dad some pottery made by his favorite local artist. This artist has no online shop and I can’t go to his store myself so I’ll have to have my mom or sister go in and buy it using my credit card number. I’m not easily accessible by phone, so they can’t just call me while they are in the shop to get my credit card number. The logical thing to do is the email them my credit card number so one of them can do it at their leisure. The problem with this is that emails get hacked all the time, what if my credit card number ends up in the wrong hands?
Instead of sending the credit card via an unencrypted message, I use my mom and sisters public keys to create an encrypted message containing my credit card information. Once they receive this message they can easily decrypt this message by unlocking it with their private key. This ensures that even if one of our emails were to be hacked, nobody would have my credit card information without also having access to one of our private keys!
If you are still confused or curious about this asymmetric encryption, here is a good YouTube video on the topic: https://www.youtube.com/watch?v=AQDCe585Lnc.