An optical encryption scheme based on a ghost imaging system with disordered speckles is proposed to obtain a higher security with a small key.In the scheme,Alice produces the random speckle pattes and obtains the detection results with the help of a computational ghost imaging (CGI) system.Then Alice permutes the order of the random speckle pattes and shares the permutation sequence as a secure key to the authorized users.With the secure key,Bob could recover the object with the principle of the CGI system,whereas,the unauthorized users could not obtain any information of the object.The numerical simulations and experimental results show that the proposed scheme is feasible with a small key,simultaneously,it has a higher security.When the eavesdropping ratio (ER) is less than 40％,the eavesdropper cannot acquire any useful information.Meanwhile,the authorized users could recover completely with the secure key.