A cryptographic device (100) arranged to compute a target block cipher (Bt) on an input message (110), the device comprising a first and second block cipher unit (121, 122) arranged to compute the target block cipher (Bt) on the input message, and a first control unit (130) arranged to take the first block cipher result and the second block cipher result as input, and to produces the first block cipher result only if the block cipher results are equal.