In this work an efficient format-compliant encryption approach for regular languages is proposed, block-based cycle-walking. The approach can transparently trade-off security for efficiency and can be adjusted to the desired level of security. The relationship between the encryption of regular languages and the encryption of JPEG2000 bitstreams is established. Block-based cycle-walking for the regular language of JPEG2000 bitstreams is compared to the extensive previous work from the multimedia security community and to the previous work from the cryptographic community, which is analyzed and evaluated.