science

NewDES

NewDES 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 NewDES rather than just read about it. In short: In cryptography, NewDES is a symmetric key block cipher. It was created in 1984–1985 by Robert Scott as a potential DES replacement.

Key takeaways

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

Reference excerpt

In cryptography, NewDES is a symmetric key block cipher. It was created in 1984–1985 by Robert Scott as a potential DES replacement. Despite its name, it is not derived from DES and has quite a different structure. Its intended niche as a DES replacement has now mostly been filled by AES. The algorithm was revised with a modified key schedule in 1996 to counter a related-key attack; this version is sometimes referred to as NewDES-96. In 2004, Scott posted some comments on sci.crypt reflecting on the motivation behind NewDES's design and what he might have done differently so as to make the cipher more secure.

Algorithm NewDES, unlike DES, has no bit-level permutations, making it easy to implement in software. All operations are performed on whole bytes. It is a product cipher, consisting of 17 rounds performed on a 64-bit data block and makes use of a 120-bit key. In each round, subkey material is XORed with the 1-byte sub-blocks of data, then fed through an S-box, the output of which is then XORed with another sub-block of data. In total, 8 XORs are performed in each round. The S-box is derived from the United States Declaration of Independence (used as a nothing-up-my-sleeve number). Each set of two rounds uses seven 1-byte subkeys, which are derived by splitting 56 bits of the key into bytes. The key is then rotated 56 bits for use in the next two rounds.

Cryptanalysis Only a small amount of cryptanalysis has been published on NewDES. The designer showed that NewDES exhibits the full avalanche effect after seven rounds: every ciphertext bit depends on every plaintext bit and key bit. NewDES has the same complementation property that DES has: namely, that if

E K ( P ) = C , {\displaystyle E_{K}(P)=C,}

then

E K ¯ ( P ¯ ) = C ¯ , {\displaystyle E_{\overline {K}}({\overline {P}})={\overline {C}},}

where

x ¯ {\displaystyle {\overline {x}}}

is the bitwise complement of x. This means that the work factor for a brute force attack is reduced by a factor of 2. Eli Biham also noticed that changing a full byte in all the key and data bytes leads to another complementation property. This reduces the work factor by 28. Biham's related-key attack can break NewDES with 233 chosen-key chosen plaintexts, meaning that NewDES is not as secure as DES. John Kelsey, Bruce Schneier, and David Wagner used related-key cryptanalysis to develop another attack on NewDES; it requires 232 known plaintexts and one related key.

References

Scott, Robert (January 1985). "Wide Open Encryption Design Offers Flexible Implementations". Cryptologia. 9 (1): 75–91. doi:10.1080/0161-118591859799. Schneier, Bruce (1996). Applied Cryptography, Second Edition. John Wiley & Sons. pp. 306–308. ISBN 978-0-471-11709-4.

External links Scott, Robert (1996-03-02). "Revision of NEWDES". Newsgroup: sci.crypt. Usenet: 4hafm9$r51@condor.ic.net. Retrieved 2018-10-10. NewDES source code implementations

Worked examples

Example 1 — a first encounter with NewDES

Start with the simplest possible case. Write down what NewDES 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 NewDES 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 NewDES 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 NewDES

In research: NewDES 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 NewDES 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: NewDES is common in secondary-school and first-year university syllabi. It links to neighbouring topics Block ciphers, Broken block ciphers, so understanding it makes those chapters shorter.
In everyday life: Look for NewDES 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 NewDES in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what NewDES 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 NewDES out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is NewDES in simple terms?

In cryptography, NewDES is a symmetric key block cipher. It was created in 1984–1985 by Robert Scott as a potential DES replacement.

Why does NewDES 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 NewDES?

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 NewDES.