Secure applications for the Internet of Things (IoT) are constantly increasing and many of them require some lightweight cryptographic algorithms. Most lightweight cryptographic algorithms were not designed to be efficient in software platforms. As a result the throughput in software of these algorithms is low on recent IoT devices. In this paper we present optimization techniques for improving the software implementation of the QUARK functions. QUARK is a family of lightweight hash functions that is efficient in hardware but its design was not oriented for software platforms. We obtained a reduction on the number of binary operations required in each iteration of QUARK, and by computing in parallel some internal functions we achieved a further speed up. In addition, we also present the results of our optimized implementations of S-QUARK and D-QUARK on the 32-bit Intel Galileo platform.9542 1151304th International Workshop on Lightweight Cryptography for Security and Privacy (LightSec)SEP 10-11, 2015Bochum, GERMANY