This paper gives a survey of the random oracle model, which is an important tool in provable security. The random oracle model is introduced on several aspects, including its origin and development, basic properties and methodology, representative schemes, plaintext awareness, random oracle instantiation, the uninstantiable properties and related negative results, and the research of weakened random oracle models. Besides, other ideal models are compared with the random oracle model, and the construction of encryption schemes in the standard model is also referred.