Patent ID: 8625806

Claim:
A data-processing apparatus comprising: a data provider implemented to provide an input datum encrypted by an encryption key; a key stream generator implemented to generate a key stream in a predetermined deterministic manner such that the key stream sequentially comprises a decryption key corresponding to the encryption key and an output key; and a data processor implemented to process the encrypted input datum in a masked manner using the decryption key as a temporary key to obtain an output datum encrypted by the output key such that the encrypted output datum corresponds to a result, encrypted by the output key, of a predetermined operation on the encrypted input datum having been decrypted by the decryption key, wherein the data processor comprises a first branch data processor implemented to apply a first mathematical or logical operation to the encrypted input datum to obtain first branch data which corresponds to a result, encrypted by second branch data, of the predetermined operation on the encrypted input datum having been decrypted by the decryption key; a second branch data processor implemented to apply a second mathematical or logical operation to the decryption key to obtain the second branch data, the first mathematical or logical operation and the second mathematical or logical operation being separated from each other in that the first mathematical or logical operation does neither involve the decryption key nor any data derived from the decryption key, and the second mathematical or logical operation does neither depend on the encrypted input datum nor any data derived from the encrypted input datum; and an XOR generator implemented to generate the encrypted output datum by XORing the first branch data, the second branch data and the output key, wherein the first branch data processor and the second branch data processor are implemented to execute as a first operation and as a second operation operational steps corresponding to operational steps of a third operation which would be applied to generate second plain text data from first plain text data, wherein the first plain text data would correspond to that data which would correspond to a decryption of the data of the encrypted input data stream by the decryption key and the second plain text data would correspond to a combination of the first branch data and the second branch data.