One of the great breakthroughs in the history of encryption was the invention of public key cryptography or asymmetrical cryptography in the 70’s. This is accomplished by the use of a pair of keys: one .
You have devices that use encryption all the time, even if you are not aware of it.
There are so many applications and systems using it that it’s hard to begin enumerating them.
Ranging from satellite television to your mobile phone, from smart power meters to your car keys, from your wireless router to your browser, and from your Visa to your Bitcoins — the list is endless.
Lets see an example: " 2048-bit RSA key, ID 96FE8CE5, created 2017-10-13 [email protected] ~ $ ls -l file* -rw-rw-r-- 1 alice alice 37 Out 13 -rw-rw-r-- 1 alice alice 287 Out 13 sig [email protected] ~ $ gpg --verify sig gpg: assuming signed data in `file.txt' gpg: Signature made Sex WEST using RSA key ID 96FE8CE5 gpg: Good signature from "Alice (Mushroom) [email protected] ~ $ gpg --verify sig gpg: assuming signed data in `file.txt' gpg: Signature made WEST using RSA key ID 96FE8CE5 gpg: BAD signature from "Alice (Mushroom) so that anyone can verify her signature.
So Alice can sign but before she can send Bob a message, Bob must also have a key pair and publish his public key somewhere or sent it to Alice.