Enrico Thomae Christopher Wolf Roots of Square: Cryptanalysis of Double-Layer Square and Square+. 83-97 2011 PQCrypto http://dx.doi.org/10.1007/978-3-642-25405-5_6 conf/pqcrypto/2011 db/conf/pqcrypto/pqcrypto2011.html#ThomaeW11