A white-box cryptographic system (600) is presented for performing a key-dependent cryptographic operation, such as AES. The system comprises a network of a plurality of look-up tables (640) arranged for collectively performing the cryptographic operation, the network being adapted for a particular cryptographic key. By sending a key substitute (664) which represents to the network a further cryptographic key a key translation unit can arrange the effect of the network on the cryptographic operation such that is adapted for a further cryptographic key. In this way the system can be updated to use the further key instead of the particular key.