Data processing method

A method for processing data in a system comprising two computers to obtain a result using at least one input data item to be supplied by at least one emitting client, the result being obtained by applying a combination of elementary operations to at least one input data item;

• wherein
• one of the computers is a server, and the other is a trusted execution environment, TEE;
• a first encryption [Enc1,Dec1] and a second encryption [Enc2,Dec2] are defined, one being indecipherable by the server, and the other being indecipherable by the TEE;
• the method includes the following steps:
• S1) at least one emitting client supplies a first input data item and applies the first encryption to it;
• S2) said at least one emitting client sends the input data item under the first encryption to one of the computers;
• S3) during a data processing operation, the two computers apply the combination of elementary operations to said encrypted data item received in step S2 so as to obtain a ciphertext of the result, and send this result to at least one receiving client, step S3 including the following elementary steps:
• S31) the first computer encrypts the processed data item under second encryption;
• S32) the first computer sends the second computers the processed data item obtained, encrypted under first and second encryption;
• and
• S33) the second computer removes the first encryption from the processed data item received;
• S4) said at least one receiving client deciphers the ciphertext of the result and obtains the result;
• during the data processing performed in step S3, the server only processes processed data under at least the encryption indecipherable by the server, and the TEE only processes processed data under at least the encryption indecipherable by the TEE, which may be in particular be masking encryption;
• and
• the first and the second encryption verify the property, for any processed data item x:
• Dec2(Dec1(Enc2(Enc1(x))))=Dec2(Enc2(x)).