As the RSA systems is probably one of the most widely used and known public key cryptosystem in the world, today I will talk about it trying to explain in detail its characteristics and complexity in order to help people to understand better this algorithm and to separate the marketing around it from maths makes possible the cryptosystem to exist.
Basically, it provides digital signatures and public key encryption based on the difficulty of factoring very large numbers and its name RSA stands for the last names of its creators, Ronald Rivest, Adi Shamir, and Leonard Adleman in 1978. The expression for the algorithm to encrypt the plain text is the following:
It is often heard that for public key encryption is required a private key and a public key, and that the sender uses the public key to encrypt the original message and the receiver utilizes its private key to decrypt the message, also that is not possible to use the public key to decrypt the original message, but we never know how those keys look like in real life for better understanding. So, I will try to go from basic to the complex little by little in order to avoid make you get confused.
First, you must know that for the case of RSA, both keys, “public” and “private” can be used to encrypt the plain text.