This Recommendation describes the confidentiality part of a privacy system suitable for use in narrow-band audiovisual services conforming to ITU-T Recs H.320, H.221, H.230 and H.242. Although an encryption algorithm is required for such a privacy system, the specifications of such algorithms are not all included here: the system caters for more than one specific algorithm. Some of those algorithms and their parameters are defined in Annex A. A privacy system consists of two parts, the confidentiality mechanism or encryption process for the data, and a key management subsystem as described in ITU-T Rec. H.234. This revised version of ITU-T Rec. H.233 introduces a number of corrections and clarifications to the original version and, more importantly, introduces the description on the usage of Triple DES and AES encryption in applicable H.320.x-series Recommendations.