A method includes receiving a request by a second user through a uniform resource locator (URL) for a user key of a shared file of a first user. The second user is a legitimate user authorized by the first user through a trust center to access the shared file. The shared file is a shared file encrypted by using the user key of the first user. A file description of the corresponding shared file is obtained from a cloud server according to the URL. The file description is a file description obtained by encrypting the user key by using a public key of the trust center. The file description is decrypted using a private key corresponding to the public key of the trust center to obtain the user key of the first user. The user key is sent to the second user.