What does a signed meter value look like?

An OCMF dataset: a JSON section with the gateway, the meter, how the user was identified and the readings at start and end, followed by the meter's signature. The meter's public key verifies it. The deep dive reads one line by line.

Explained in

Payments and billing · Deep diveThe signed meter values of one sessionThe commuter's 38.20 kWh as the charger's meter signed them: one OCMF dataset with gateway, meter, identification, two readings and the signature, and the public key that verifies it.
  • Covered. The readings, their times, the register, the meter's identity and the identification of the user, all in one hash. A changed digit anywhere breaks the signature.
  • Not covered. The price, the tariff, the driver's name and the invoice. Those come from the backend and the provider; measuring law protects the measurement, contract law the price.
  • The charger around the meter. The charge controller supplies the card's identifier and passes the signed dataset on over OCPP, but cannot change it without breaking the signature. When the meter is the signing component, its serial number alone identifies the public key.
From “What the signature covers, and what it leaves out”, stop 09

Terms

  1. OCPPOpen Charge Point Protocol: the open protocol between a charger and its operator's backend.
  2. OCMFOpen Charge Metering Format: the common container for signed meter readings of a charging session, with gateway, meter, identification, readings and signature, kept by SAFE e.V.
  1. How is a charging price made up?From a price per kWh, per minute, per session and any other component. At 50 kW and above, the ad hoc price is based on kWh, with an optional fee per minute.
  2. Can I pay by bank card at a charger?At public charge points deployed since April 2024, yes: operators must accept card readers, contactless devices or, below 50 kW, internet payment such as a QR code.
  3. Is charging abroad more expensive with my card?Providers must show all price components before a session and may not apply extra charges for cross-border e-roaming in the EU.
  4. What must be on a charging invoice?On a full invoice under the EU VAT Directive: date, sequential number, VAT numbers, names and addresses, quantity, unit price, VAT rate and amount; up to 100 EUR, a simplified invoice with fewer details is allowed. Session details such as site, times and kWh make it easy to check.
  1. SAFE e.V.: OCMF, Open Charge Metering Format: specification on GitHub. https://github.com/SAFE-eV/OCMF-Open-Charge-Metering-Format. Checked 13 Oct 2026.