Encryption and decryption information system

The invention discloses a file encryption method and device and a file decryption method and device. The file encryption method comprises the steps: receiving a file downloading request transmitted bya client, and obtaining a corresponding target file according to the file downloading request; determining the confidentiality level of the target file; when the confidentiality level of the target file is a first-level confidentiality level, generating a group of temporary key pairs; encrypting the first key by using a pre-stored server private key and a public key of the client, obtaining a first encrypted file, and transmitting the first encrypted file to the client, so as to enable the client to decrypt the first encrypted file by using a pre-stored server public key corresponding to theserver private key and a client private key corresponding to the public key of the client to obtain a first secret key; and encrypting the target file by using the second key to obtain a second encrypted file, and transmitting