What is RSA encryption? and how secure is it? what is it's main disadvantage(s)? and which encryption function could replace? :)

RSA is an Asymmetric encrytion function used to transfer information securely between two entities, mainly to exchange session keys (Like AES keys). The reason why its not used to transfer messages instead of AES is because it takes a lot of computation power to calculate one cipher block compared to symmetric cipher block calculations like AES. This disadvantage happened because of there is a weakness in RSA key size less than RSA-1024 makes subject to mathematical cryptanlysis Continues Fraction. The future asymmetric function could be NTRU or Elliptic Curve cryptography ECC

Thanks for the invitation. I support the answer given by Abdulla Alrashidi.