The Standard Transfer Specification (STS) describes a secure message system for carrying information between a point-of-sale and a meter, and is currently finding wide application in electricity metering and payment systems. STS is not limited to this application (see the section: Future enhancements), but because of the wide interest in this area, this document describes the electricity application. STS is an international industry standard described in IEC62055-41, -51 and -52.