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.
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