RSA public key cryptosystem is a cryptosystem that uses different encryption keys and decryption keys. "It is computationally infeasible to derive the decryption key from the known encryption key."
1. Detailed introduction
In the public key cryptography system, the encryption key (i.e., the public key) PK is public information, and the decryption key (i.e., the secret key) SK needs to keep it confidential.
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 based on 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 and is saved by the user; the other is a public key. The key can be made public or even registered in a network server.
To improve confidentiality, the RSA key must be at least 500 bits long. This makes encryption computationally expensive. In order to reduce the amount of calculation, when transmitting information, a combination of traditional encryption methods and public key encryption methods is often used.
That is, the information is encrypted using an improved DES or IDEA conversation key, and then an RSA key is used to encrypt the conversation key and message digest. After the other party receives the message, it uses different keys to decrypt it and can check the message summary.
RSA is the most widely studied public key algorithm. It has been nearly thirty years since it was proposed. It has experienced various attacks and has gradually been accepted by people. It is generally considered to be the best public key algorithm at present. One of the key schemes. In 1983, MIT applied for a patent for the RSA algorithm in the United States.
RSA allows you to choose the size of the public key. 512-bit keys are considered insecure; 768-bit keys do not need to be compromised by anything other than the National Security Administration (NSA);
RSA is embedded in some major products , like Windows, Netscape Navigator, Quicken and Lotus Notes.
Since the 1024-bit key of the RSA algorithm faces serious security threats, in order to ensure the safe application of electronic authentication services, on December 5, 2016, the Shanghai Cryptozoology Administration issued an announcement on its official website, stating that from Starting from January 1, 2017, we will stop providing RSA algorithm 1024-bit key pair services.