1. Choose two big prime numbers, p and q.

2. calculation: n = p * q (p and q are two different big prime numbers and must be kept secret. Generally, P and Q are required to be safe prime numbers, and the length of N is greater than 5 12bit, mainly because the security of RSA algorithm depends on the factorization of large numbers). There is Euler function (n)=(p- 1)(q- 1).

3. Then the encryption key E is randomly selected, and it is required that E and (p- 1) * (q- 1) are prime numbers.

4. Finally, use Euclid algorithm to calculate the decryption key D, which satisfies de≡ 1(mod φ(n)). Where n and d are also coprime. Numbers e and n are public keys and d is private key. Two prime numbers, P and Q, are no longer needed and should be discarded so that no one knows.

Encryption and decryption algorithm:

1. When encrypting information m (binary representation), first divide m into equal-length data blocks m 1, m2, ..., mi, with block length of s, where 2 s.

2. The corresponding ciphertext is: ci ≡mi^e (mod n) (a (a).

3. The following calculation is made during decryption: m ≡ ci d (mod n) (b) RSA can be used for digital signature, and the scheme is to use (a) signature and (b) verification.