| CPC H04L 9/008 (2013.01) [H04L 9/0822 (2013.01)] | 14 Claims |

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1. A method for encrypting data of a field device, comprising:
generating data using the field device;
encrypting the data by the field device using a non-homomorphic encryption method using a first key;
transmitting the non-homomorphically encrypted data to a first instance;
storing the non-homomorphically encrypted data in the first instance;
retrieving at least a part of the non-homomorphically encrypted data stored in the first instance by a second instance;
decrypting the retrieved, non-homomorphically encrypted data using the second instance using the first key;
encrypting the data by the second instance by means of a homomorphic encryption method using a second key;
transmitting the homomorphically encrypted data to the first instance or a third instance;
storing the homomorphically encrypted data in the first instance or in the third instance; and
supplying the field device with electrical energy required for operation from at least one of, an energy storage unit included as a part of the field device or a communication network wherein the field device is embedded.
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