Key Expansion in Cryptographic Systems

The manner in which a secret key is used in symmetric cryptographic systems is a permanent challenge for cryptographers due to its importance in overall security required for information protection. In order to mitigate the success rate of an attacker, a key expansion stage is included in cryptographic algorithms. This article presents an innovative solution that maximizes the key space, without reveal any information to an attacker who might monitor the communication channel. The prerequisites of this approach are the secret keys, a pseudorandom numbers generator and a random number generator, all of these being aggregate by a challenge-response mutual authentication protocol and a permutation function. For an efficient implementation, the already existing conductive mesh and the associated electronic circuits, dedicated to protect the cryptographic module against physical intrusion attempts of an attacker, are used to generate random numbers, without being necessary other electronic circuits. The numbers established as a result of the mutual authentication protocol will be used further to permute the secret key so, after each logical (re)synchronization, different keys will be used in cipher algorithm. Due to this key space extension process, the confusion and diffusion properties belonging to cypher algorithm are improved.