Format-compliant encryption of JPEG2000 has attracted researchers for several years. Most benefits of format-compliant encryption result from the preservation of code-stream features, such as scalability. The possibility of reducing the complexity of encryption and to realize transparent encryption schemes are among the additional features of format-compliant selective encryption. Wu and Deng have proposed a format-compliant iterative encryption scheme for JPEG2000 on a CCP basis. In this paper we discuss whether it is possible to extend this approach to packet bodies and give an exact formula for the expected computational effort. The theoretical results are cross-verified by an experimental survey.