science

LOKI97

LOKI97 is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand LOKI97 rather than just read about it. In short: In cryptography, LOKI97 is a block cipher which was a candidate in the Advanced Encryption Standard competition. It is a member of the LOKI family of ciphers, with earlier instances being LOKI89 and LOKI91.

Key takeaways

LOKI97 belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect LOKI97 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of LOKI97 from memory before moving on to harder problems.

Reference excerpt

In cryptography, LOKI97 is a block cipher which was a candidate in the Advanced Encryption Standard competition. It is a member of the LOKI family of ciphers, with earlier instances being LOKI89 and LOKI91. LOKI97 was designed by Lawrie Brown, assisted by Jennifer Seberry and Josef Pieprzyk. Like DES, LOKI97 is a 16-round Feistel cipher, and like other AES candidates, has a 128-bit block size and a choice of a 128-, 192- or 256-bit key length. It uses 16 rounds of a balanced Feistel network to process the input data blocks (see diagram right). The complex round function f incorporates two substitution-permutation layers in each round. The key schedule is also a Feistel structure – an unbalanced one unlike the main network — but using the same F-function.

The LOKI97 round function (shown right) uses two columns each with multiple copies of two basic S-boxes. These S-boxes are designed to be highly non-linear and have a good XOR profile. The permutations before and between serve to provide auto-keying and to diffuse the S-box outputs as quickly as possible. The authors have stated that, "LOKI97 is a non-proprietary algorithm, available for royalty-free use worldwide as a possible replacement for the DES or other existing block ciphers." It was intended to be an evolution of the earlier LOKI89 and LOKI91 block ciphers. It was the first published candidate in the Advanced Encryption Standard competition, and was quickly analysed and attacked. An analysis of some problems with the LOKI97 design, which led to its rejection when shortlisting candidates, is given in a paper (Rijmen & Knudsen 1999). It was found to be susceptible to an effective theoretical differential cryptanalysis attack considerably faster than an exhaustive search.

See also LOKI Advanced Encryption Standard competition

References L. Brown, J. Pieprzyk: Introducing the new LOKI97 Block Cipher L.R. Knudsen and V. Rijmen, "Weaknesses in LOKI97", Proceedings of the 2nd AES Candidate Conference, Rome, March 22–23, 1999, pp. 168–174. Wenling Wu, Bao Li, Denguo Feng, Sihan Qing, "Cryptanalysis of some AES candidate algorithms", Information and Communication Security - ICICS'99, LNCS 1726, pp 13–21, V Varadharajan (ed), Springer-Verlag 1999. Wenling Wu, Bao Li, Denguo Feng, Sihan Qing, "Linear cryptanalysis of LOKI97", Journal of Software, vol 11 no 2, pp 202–6, Feb 2000.

External links The LOKI97 homepage The design of LOKI97 SCAN's entry for LOKI97 John Savard's Description of LOKI97 Online-implementation of LOKI97 at serversniff.net

Illustrations

LOKI97: Overall LOKI97 cipher structure — Overall LOKI97 cipher structure

Worked examples

Example 1 — a first encounter with LOKI97

Start with the simplest possible case. Write down what LOKI97 claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to LOKI97 before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about LOKI97 ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of LOKI97

In research: LOKI97 appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses LOKI97 in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: LOKI97 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Block ciphers, Broken block ciphers, Feistel ciphers, so understanding it makes those chapters shorter.
In everyday life: Look for LOKI97 outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study LOKI97 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what LOKI97 means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain LOKI97 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is LOKI97 in simple terms?

Why does LOKI97 matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study LOKI97?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on LOKI97.