  Internet of Things connects lots of small constrained devices to the
Internet. As in any other environment, communication security is important and
cryptographic algorithms are one of many elements that we use in order to keep
messages secure. Because of the constrained nature of these environments, it is
necessary to use algorithms that do not require high computational power.
Lightweight ciphers are therefore ideal candidates for this purpose.
  In this paper, we explore a possibility of attacking an ultra-lightweight
cipher PRESENT by using a multiple fault attack. Utilizing the Differential
Fault Analysis technique, we were able to recover the secret key with two
faulty encryptions and an exhaustive search of 2^16 remaining key bits. Our
attack aims at four nibbles in the penultimate round of the cipher, causing
faulty output in all nibbles of the output. We also provide a practical attack
scenario by exploiting Hardware Trojan (HT) technique for the proposed fault
injection in a Xilinx Spartan-6 FPGA.
