[Free/Open Source] RSA asymmetric cryptography extension. Encrypt, decrypt, sign and check signatures with asymmetric cryptography, direct and asynchronous

Symmetric encryption like AES. Still you need to know a lot about (a)symmetric encryption, otherwise it is possible that the encryption used, is not safe enough at all.
https://www.wikiwand.com/en/Advanced_Encryption_Standard

What is the difference between Encrypt and Async Encrypt ??

Have you read the first and fourth post?

Yes, but I did not understand what was meant by * Performs encryption and decryption asynchronously to avoid blocking the UI and * Raises events Encrypted and Decrypted with the result.