Lars Knudsen
Encyclopedia
Denmark
Denmark is a Scandinavian country in Northern Europe. The countries of Denmark and Greenland, as well as the Faroe Islands, constitute the Kingdom of Denmark . It is the southernmost of the Nordic countries, southwest of Sweden and south of Norway, and bordered to the south by Germany. Denmark...
researcher in cryptography
Cryptography
Cryptography is the practice and study of techniques for secure communication in the presence of third parties...
, particularly interested in the design and analysis
Cryptanalysis
Cryptanalysis is the study of methods for obtaining the meaning of encrypted information, without access to the secret information that is normally required to do so. Typically, this involves knowing how the system works and finding a secret key...
of block cipher
Block cipher
In cryptography, a block cipher is a symmetric key cipher operating on fixed-length groups of bits, called blocks, with an unvarying transformation. A block cipher encryption algorithm might take a 128-bit block of plaintext as input, and output a corresponding 128-bit block of ciphertext...
s, hash functions
Cryptographic hash function
A cryptographic hash function is a deterministic procedure that takes an arbitrary block of data and returns a fixed-size bit string, the hash value, such that an accidental or intentional change to the data will change the hash value...
and message authentication code
Message authentication code
In cryptography, a message authentication code is a short piece of information used to authenticate a message.A MAC algorithm, sometimes called a keyed hash function, accepts as input a secret key and an arbitrary-length message to be authenticated, and outputs a MAC...
s (MACs).
Academic
After some early work in banking, Knudsen enrolled at Aarhus University in 1984 studying mathematicsMathematics
Mathematics is the study of quantity, space, structure, and change. Mathematicians seek out patterns and formulate new conjectures. Mathematicians resolve the truth or falsity of conjectures by mathematical proofs, which are arguments sufficient to convince other mathematicians of their validity...
and computer science
Computer science
Computer science or computing science is the study of the theoretical foundations of information and computation and of practical techniques for their implementation and application in computer systems...
, gaining an MSc in 1992 and a PhD in 1994. From 1997-2001, he worked at the University of Bergen
University of Bergen
The University of Bergen is located in Bergen, Norway. Although founded as late as 1946, academic activity had taken place at Bergen Museum as far back as 1825. The university today serves more than 14,500 students...
, Norway
Norway
Norway , officially the Kingdom of Norway, is a Nordic unitary constitutional monarchy whose territory comprises the western portion of the Scandinavian Peninsula, Jan Mayen, and the Arctic archipelago of Svalbard and Bouvet Island. Norway has a total area of and a population of about 4.9 million...
. Currently, Knudsen is a professor in the Department of Mathematics
Mathematics
Mathematics is the study of quantity, space, structure, and change. Mathematicians seek out patterns and formulate new conjectures. Mathematicians resolve the truth or falsity of conjectures by mathematical proofs, which are arguments sufficient to convince other mathematicians of their validity...
at the Technical University of Denmark
Technical University of Denmark
The Technical University of Denmark , often simply referred to as DTU, is a university just north of Copenhagen, Denmark. It was founded in 1829 at the initiative of Hans Christian Ørsted as Denmark's first polytechnic, and is today ranked among Europe's leading engineering institutions, and the...
. His Erdős number
Erdos number
The Erdős number describes the "collaborative distance" between a person and mathematician Paul Erdős, as measured by authorship of mathematical papers.The same principle has been proposed for other eminent persons in other fields.- Overview :...
is 3, via his work with noted cryptographers Don Coppersmith
Don Coppersmith
Don Coppersmith is a cryptographer and mathematician. He was involved in the design of the Data Encryption Standard block cipher at IBM, particularly the design of the S-boxes, strengthening them against differential cryptanalysis...
and Ivan Damgård
Ivan Damgård
Ivan Bjerre Damgård is a Danish cryptographer and currently a professor at the Department of Computer Science , Aarhus University, Denmark....
. Ivan 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
Differential cryptanalysis
Differential cryptanalysis is a general form of cryptanalysis applicable primarily to block ciphers, but also to stream ciphers and cryptographic hash functions. In the broadest sense, it is the study of how differences in an input can affect the resultant difference at the output...
. His Ph.D. was refereed by Bart Preneel
Bart Preneel
Bart Preneel is a Belgian cryptographer and cryptanalyst. He is a professor at Katholieke Universiteit Leuven, in the COSIC group, president of the International Association for Cryptologic Research, and project manager of ECRYPT....
.
Publications
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 cipherCipher
In cryptography, a cipher is an algorithm for performing encryption or decryption — a series of well-defined steps that can be followed as a procedure. An alternative, less common term is encipherment. In non-technical usage, a “cipher” is the same thing as a “code”; however, the concepts...
s: DES
Data Encryption Standard
The Data Encryption Standard is a block cipher that uses shared secret encryption. It was selected by the National Bureau of Standards as an official Federal Information Processing Standard for the United States in 1976 and which has subsequently enjoyed widespread use internationally. It is...
, DFC
DFC (cipher)
In cryptography, DFC is a block cipher which wascreated in 1998 by a group of researchers from École Normale Supérieure, CNRS, and France Télécom and submitted to the AES competition.Like other AES candidates, DFC operates on blocks of 128 bits, using a key of 128, 192, or 256 bits...
, IDEA, ICE
ICE (cipher)
In cryptography, ICE is a block cipher published by Kwan in 1997. The algorithm is similar in structure to DES, but with the addition of a key-dependent bit permutation in the round function. The key-dependent bit permutation is implemented efficiently in software...
, LOKI
LOKI
In cryptography, LOKI89 and LOKI91 are block ciphers designed as possible replacements for the Data Encryption Standard . The ciphers were developed based on a body of work analysing DES, and are very similar to DES in structure...
, MISTY
Misty
Misty may refer to:* Misty , a United States satellite program* Misty , a British comic published from 1978 to 1984* Misty , a 1961 adaptation of the book Misty of Chincoteague by Marguerite Henry...
, RC2
RC2
In cryptography, RC2 is a block cipher designed by Ron Rivest in 1987. "RC" stands for "Ron's Code" or "Rivest Cipher"; other ciphers designed by Rivest include RC4, RC5 and RC6....
, RC5
RC5
In cryptography, RC5 is a block cipher notable for its simplicity. Designed by Ronald Rivest in 1994, RC stands for "Rivest Cipher", or alternatively, "Ron's Code"...
, RC6
RC6
In cryptography, RC6 is a symmetric key block cipher derived from RC5. It was designed by Ron Rivest, Matt Robshaw, Ray Sidney, and Yiqun Lisa Yin to meet the requirements of the Advanced Encryption Standard competition. The algorithm was one of the five finalists, and was also submitted to the...
, SC2000
SC2000
In cryptography, SC2000 is a block cipher invented by a research group at Fujitsu Labs. It was submitted to the NESSIE project, but was not selected. SC2000 is one of the cryptographic techniques recommended for Japanese government use by CRYPTREC....
, Skipjack
Skipjack (cipher)
In cryptography, Skipjack is a block cipher—an algorithm for encryption—developed by the U.S. National Security Agency . Initially classified, it was originally intended for use in the controversial Clipper chip...
, Square
Square (cipher)
In cryptography, Square is a block cipher invented by Joan Daemen and Vincent Rijmen. The design, published in 1997, is a forerunner to the Rijndael algorithm, which has been adopted as the Advanced Encryption Standard...
and SAFER
SAFER
In cryptography, SAFER is the name of a family of block ciphers designed primarily by James Massey on behalf of Cylink Corporation. The early SAFER K and SAFER SK designs share the same encryption function, but differ in the number of rounds and the key schedule...
—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
DEAL
In cryptography, DEAL is a block cipher derived from the Data Encryption Standard . The design was proposed in a report by Lars Knudsen in 1998, and was submitted to the AES contest by Richard Outerbridge .DEAL is a Feistel network which uses DES as the...
and Serpent
Serpent (cipher)
Serpent is a symmetric key block cipher which was a finalist in the Advanced Encryption Standard contest, where it came second to Rijndael. Serpent was designed by Ross Anderson, Eli Biham, and Lars Knudsen....
(the latter in conjunction with Ross Anderson and Eli Biham
Eli Biham
Eli Biham is an Israeli cryptographer and cryptanalyst, currently a professor at the Technion Israeli Institute of Technology Computer Science department. Starting from October 2008, Biham is the dean of the Technion Computer Science department, after serving for two years as chief of CS graduate...
). He is one of the designers of Grøstl
Grøstl
Grøstl is a cryptographic hash function submitted to the NIST hash function competition by Praveen Gauravaram, Lars Knudsen, Krystian Matusiewicz, Florian Mendel, Christian Rechberger, Martin Schläffer, and Søren S. Thomsen. Grøstl was chosen as one of the five finalists of the competition. It uses...
, a hash function which is one of the five finalists in the NIST SHA-3 competition.
He introduced the technique of impossible differential cryptanalysis
Impossible differential cryptanalysis
In cryptography, impossible differential cryptanalysis is a form of differential cryptanalysis for block ciphers. While ordinary differential cryptanalysis tracks differences that propagate through the cipher with greater than expected probability, impossible differential cryptanalysis exploits...
and integral cryptanalysis
Integral cryptanalysis
In cryptography, integral cryptanalysis is a cryptanalytic attack that is particularly applicable to block ciphers based on substitution-permutation networks. It was originally designed by Lars Knudsen as a dedicated attack against Square, so is commonly known as the Square attack. It was also...
.