RSA public key cryptosystem. The so-called public key cryptosystem uses different encryption keys and decryption keys.
In the
public
key cryptosystem , the encryption key (ie the public key) PK is public information, and the decryption key (ie the secret key) SK needs to be kept secret.
Both encryption algorithm
E and decryption algorithm D are also public. Although the decryption key SK is determined by the public key PK, SK cannot be calculated from the PK.
It is based on this theory that the famous RSA algorithm appeared in 1978. It usually generates a pair of RSA keys first, one of which is a secret key, which is kept by the user; the other is a public key, which can be disclosed to the public, even Can be registered in the
web
server . To improve confidentiality, the RSA key should be at least 500 bits long, and 1024 bits are generally recommended. This makes encryption computationally expensive. In order to reduce the amount of calculation, when transmitting information, a combination of
traditional encryption method and public key encryption method is often used, that is, the information is encrypted with an improved DES or IDEA session key
, and then the session key and information are encrypted with an RSA key. Summary. After receiving the information, the other party decrypts it with a different key and can check the information digest.
The RSA algorithm is the first algorithm that can be used for both encryption and
digital
signatures , and is also easy to understand and operate. RSA is the most widely studied
public key
algorithm. In the more than 30 years since it was proposed to the present, it has experienced the test of various attacks and has gradually been accepted by people. It is generally considered to be one of the best public key schemes at present.