International Association
for Cryptologic Research

In this paper we study a scan based side channel attack

against the Grain family of stream ciphers. The attack works

because scan chain test of circuits can be transformed into a

powerful cryptographic attack due to the properties of scan

based technique. So as a result the attack targets the test

circuitry. We show how the attacker gains the knowledge about

the locations of internal state bits of the NFSR and the LFSR and

how he finds the secret key.