In 1993, Rijmen obtained a degree in electronics engineering at the Katholieke Universiteit Leuven. Afterwards, he was a PhD student at the ESAT/COSIC lab of the K.U.Leuven. In 1997, Rijmen finished his doctoral dissertation titled Cryptanalysis and design of iterated block ciphers.
Since 1 August 2001, Rijmen has been working as chief cryptographer at Cryptomathic where he cooperated with cryptographers such as Peter Landrock.[2] From 2001 to 2003, Rijmen was a visiting professor at the Institute for Applied Information Processing and Communications at Graz University of Technology (Austria), and a full professor there from 2004 to 2007. Since October 2007, Rijmen has worked again with the COSIC lab and currently holds a professor position (gewoon hoogleraar) at K.U.Leuven. Since January 2019 he is also an adjunct professor at Selmer Center (the secure communication group at the University of Bergen, Norway).
In 2002, he was named by the MITTechnology ReviewTR100 as one of the top 100 innovators in the world under the age of 35.[3]
^"Announcing the ADVANCED ENCRYPTION STANDARD (AES)"(PDF). NIST Federal Information Processing Standards Publication 197. United States National Institute of Standards and Technology (NIST). November 26, 2001. Retrieved October 2, 2012.