The concept of public library are the "super-relays", which are always available and basically accept any note you send their way.
It is "kind of" like reinventing email with PGP. Main difference is that you can choose to send the message in plain text with a cryptographic signature that proves it was sent from you or full encrypted like PGP.
There is still (in my opinion) a disadvantage when compared to PGP: key rotation. Once you create a key pair in NOSTR it is your identity forever, whereas in PGP you have mechanisms to declare a key obsolete and generate a new one.
In overall PGP failed over the last 30 years, sharing public keys with other people was always the biggest difficulty for real adoption. With NOSTR this process is kind of solved but we are yet to see about adoption.
It is "kind of" like reinventing email with PGP. Main difference is that you can choose to send the message in plain text with a cryptographic signature that proves it was sent from you or full encrypted like PGP.
There is still (in my opinion) a disadvantage when compared to PGP: key rotation. Once you create a key pair in NOSTR it is your identity forever, whereas in PGP you have mechanisms to declare a key obsolete and generate a new one.
In overall PGP failed over the last 30 years, sharing public keys with other people was always the biggest difficulty for real adoption. With NOSTR this process is kind of solved but we are yet to see about adoption.