|Lars R. Knudsen|
|Born||21 February 1962|
|Alma mater||Aarhus University|
|Institutions||Technical University of Denmark|
|Doctoral advisor||Ivan Damgård|
|Doctoral students||Søren Thomsen|
Lars Ramkilde Knudsen (born 21 February 1962) is a Danish researcher in cryptography, particularly interested in the design and analysis of block ciphers, hash functions and message authentication codes (MACs).
After some early work in banking, Knudsen enrolled at Aarhus University in 1984 studying mathematics and computer science, gaining an MSc in 1992 and a PhD in 1994. From 1997-2001, he worked at the University of Bergen, Norway. Currently, Knudsen is a professor in the Department of Mathematics at the Technical University of Denmark. Ivan Damgård was Lars' teacher and mentor during his studies at Aarhus University, and according to Lars was a deciding factor in his choice to study differential cryptanalysis. His Ph.D. was refereed by Bart Preneel.
Knudsen has published analyses of a wide variety of cryptographic designs, including the R-MAC scheme, the SHA-1 and MD2 hash functions, and at least a dozen block ciphers: DES, DFC, IDEA, ICE, LOKI, MISTY, RC2, RC5, RC6, SC2000, Skipjack, Square and SAFER—it has been hinted that the "SK" in the "SAFER-SK" variant means Stop Knudsen after he had found weaknesses in a previous version.
Knudsen has also designed ciphers, including the AES candidates DEAL and Serpent (the latter in conjunction with Ross Anderson and Eli Biham). He is one of the designers of Grøstl, a hash function which was one of the five finalists in the NIST SHA-3 competition.