Somitra Kumar Sanadhya Palash Sarkar Non-linear Reduced Round Attacks against SHA-2 Hash Family. 254-266 2008 ACISP http://dx.doi.org/10.1007/978-3-540-70500-0_19 conf/acisp/2008 db/conf/acisp/acisp2008.html#SanadhyaS08