RSA public key cryptosystem is a cryptosystem that uses different encryption keys and decryption keys. It is computationally infeasible to derive decryption keys from known encryption keys. .
In a public key cryptosystem, the encryption key PK is public information, while the decryption key SK needs to be kept secret. An encryption algorithm e and a decryption algorithm d are also disclosed. Although the decryption key SK is determined by the public key PK, it cannot be calculated from PK.
Based on this theory, the famous RSA algorithm appeared in 1978, which is usually a pair of RSA keys, one of which is a secret key and kept by the user. The other is the public key, which can be made public or even registered on the network server. In order to improve the security strength, the length of RSA key should be at least 500 bits. This makes the calculation of encryption very large.
In order to reduce the amount of calculation, when transmitting information, the traditional encryption method is often combined with the public key encryption method, that is, the information is encrypted with the improved DES or IDEA dialogue key, and then the dialogue key and message digest are encrypted with RSA key. After receiving the message, the other party can decrypt it with different keys and view the message summary.
RSA is the most widely studied public key algorithm. It has been nearly 30 years since it was put forward. Tested by various attacks, it is gradually accepted by people. It is generally considered as one of the best public key schemes at present. 1983 MIT applied for RSA algorithm patent in the United States? .