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RC2

RC2 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 RC2 rather than just read about it. In short: In cryptography, RC2 (also known as ARC2) is a symmetric-key block cipher designed by Ron Rivest in 1987. "RC" stands for "Ron's Code" (see also RC2, RC5 and RC6), but generally called simply RC2. Other ciphers designed by Ron Rivest include RC4, RC5, and RC6.

RC2 — main illustration
RC2 — illustration

Key takeaways

  • RC2 belongs to science; place it in that map before memorising details.
  • Learn the definition first, then one example that makes the definition concrete.
  • Connect RC2 to a quantity you can measure, compute or draw — that is where exam questions come from.
  • Reproduce the core statement of RC2 from memory before moving on to harder problems.

Reference excerpt

In cryptography, RC2 (also known as ARC2) is a symmetric-key block cipher designed by Ron Rivest in 1987. "RC" stands for "Ron's Code" (see also RC2, RC5 and RC6), but generally called simply RC2. Other ciphers designed by Ron Rivest include RC4, RC5, and RC6. The development of RC2 was sponsored by Lotus, who were seeking a custom cipher that, after evaluation by the NSA, could be exported as part of their Lotus Notes software. The NSA suggested a few changes, which Rivest incorporated. After further negotiations, the cipher was approved for export in 1989. Along with RC4, RC2 with a 40-bit key size was treated favourably under US export regulations for cryptography. Initially, the details of the algorithm were kept secret — proprietary to RSA Security — but on 29 January 1996, source code for RC2 was anonymously posted to the Internet on the Usenet forum sci.crypt. Mentions of CodeView and SoftICE (popular debuggers) suggest that it had been reverse engineered. A similar disclosure had occurred earlier with RC4. In March 1998, Ron Rivest authored an RFC publicly describing RC2 himself. RC2 is a 64-bit block cipher with a variable size key. Its 18 rounds are arranged as a source-heavy unbalanced Feistel network, with 16 rounds of one type (MIXING) punctuated by two rounds of another type (MASHING). A MIXING round consists of four applications of the MIX transformation, as shown in the diagram. RC2 is vulnerable to a related-key attack using 234 chosen plaintexts.

References

Bibliography

External links RFC 2268 - A Description of the RC2(r) Encryption Algorithm RSA FAQ: What is RC2? Archived 2016-03-03 at the Wayback Machine sci.crypt posting revealing the RC2 algorithm

Illustrations

RC2 illustration

Worked examples

Example 1 — a first encounter with RC2

Start with the simplest possible case. Write down what RC2 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 RC2 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 RC2 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 RC2

In research
RC2 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 RC2 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
RC2 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 RC2 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 RC2 in 20 minutes

  1. Read the reference excerpt below once, without taking notes.
  2. Close the page and write down what RC2 means in your own words.
  3. Compare your version with the excerpt and mark what you missed.
  4. Work through the three examples above with pen and paper.
  5. Explain RC2 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is RC2 in simple terms?

In cryptography, RC2 (also known as ARC2) is a symmetric-key block cipher designed by Ron Rivest in 1987. "RC" stands for "Ron's Code" (see also RC2, RC5 and RC6), but generally called simply RC2. Other ciphers designed by Ron Rivest include RC4, RC5, and RC6.

Why does RC2 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 RC2?

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 RC2.

Tags

  • Block ciphers
  • Broken block ciphers

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