Making prepayment meters future proof

State of the art encryption in a new edition of IEC 62055-41

IEC TC 13: Electrical energy management and control, has published a new Standard which significantly enhances the security of electricity metering prepayment systems, widely used in developing countries around the world.


electricity in South Africa
Many people in developing countries buy their electricity in advance (Photo: Graham Maclachlan)

IEC 62055-41, Electricity metering – Payment systems – Part 41: Standard transfer specification (STS) - Application layer protocol for one-way token carrier systems replaces the previous edition of the Standard published in 2014. It is also published as a Red Line Version (RLV), which clearly highlights all the changes in the new Standard. Additions and deletions are displayed in red, with deletions being struck through.

“We wanted to improve the encryption algorithms drastically and make them state of the art secure. The idea is for the encryption levels to be valid for the next 30 years,” explains Don Taylor, convenor of Joint Working Group (JWG)16 which was set up within IEC TC 57: Power systems management and associated information exchange. “TC 57 started looking at smart meters around ten years ago and we formed a joint working group to make sure that our smart metering and prepayment Standards were harmonized with their metering specifications,” he adds.

Don Taylor is also an active member of WG 14: Data exchange for meter reading, tariff and load control and of WG 15: Smart metering functions and processes. Furthermore, he is the chair of the Standard Transfer Specification (STS) association, the custodian of the STS prepayment metering technology Standard, initiated in South Africa and adopted by the IEC as IEC 62055-41 and IEC 62055-51 International Standards on prepayment meters.

According to Don Taylor, there are around 50 million prepayment meters deployed in 102 countries at present. “This comprises most African countries, many South East Asian and Middle Eastern nations as well as many South American countries,” he says.

A metering solution adapted to developing nations

Current prepayment systems are based on a 20 digit token solution which enables consumers to buy their electricity in advance. “Most people living in developing nations find it very difficult to predict how much money they will have left at the end of the month. Salaries are often paid in weekly wages and a monthly electricity billing system, similar to what exists in Europe or the USA, would be totally unpractical,” Taylor continues.

The previous edition of IEC 62055-41 made specifications based on the Data Encryption Standard (DES), an encryption algorithm which is now considered too weak. The new edition is based on the MISTY1 cryptographic algorithm which uses a 128-bit decoder key.

“We wanted  the encryption to be as future proof as possible. While there has yet to be any evidence of cyber attacks on metering prepayment systems, they could happen one day and we have to be prepared. We also want to be ready for smart grids and smart meters,” Taylor indicates.

While the new Standard is applicable only to one-way token carrier systems, the STS association is working on a two-way carrier system. “The STS association will make a proposal for TC 13 to consider. I would expect a two-way edition of the Standard to be published in a couple of years,” Taylor concludes.