[Tutorial] Understand the authentication principle of public key cryptography

 This article is continue of encryption principle of public key cryptography :

[Tutorial] Understand the encryption principle of public key cryptography 

Then how Sarah can identify the message is from John but not from Tom, Timmy and Sam ?
John can create a pairs of key (public key and private) and a box.

1. John put his message into a box created by him,
2. lock his box by his private key he just created.
3. and put this box and a copy of public key created by John inside Sarch's box.
4. Lock Sarah's box by Sarah's public key provided from Sarah

After these steps, what john send Sarah would look like this:

When Sarah receive the box from John, She use her private key to unlock her outer box, and then use public key provided by John to unlock John 's box.

Since there is only one private key and owned by John, only John can lock message (encrypt) with his private key. If Sarah able use a public key received by John to unlock (decrypt) message, This mean message are from John.

Reference 

https://www.thenewslens.com/article/31591