science

RC6

RC6 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 RC6 rather than just read about it. In short: 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 (AES) competition.

RC6 — main illustration — RC6 — illustration

Key takeaways

RC6 belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect RC6 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of RC6 from memory before moving on to harder problems.

Reference excerpt

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 (AES) competition. The algorithm was one of the five finalists, and also was submitted to the NESSIE and CRYPTREC projects. It was a proprietary algorithm, patented by RSA Security. According to Ron Rivest, the RC stands for Ron's Code, but the RC documentation says simply RC6. RC6 proper has a block size of 128 bits and supports key sizes of 128, 192, and 256 bits up to 2040-bits, but, like RC5, it may be parameterised to support a wide variety of word-lengths, key sizes, and number of rounds. RC6 is very similar to RC5 in structure, using data-dependent rotations, modular addition, and XOR operations; in fact, RC6 could be viewed as interweaving two parallel RC5 encryption processes, although RC6 does use an extra multiplication operation not present in RC5 in order to make the rotation dependent on every bit in a word, and not just the least significant few bits.

Encryption/decryption The key expansion algorithm is practically identical to that of RC5. The only difference is that for RC6, more words are derived from the user-supplied key.

Possible use in NSA "implants" In August 2016, code reputed to be Equation Group or NSA "implants" for various network security devices was disclosed. The accompanying instructions revealed that some of these programs use RC6 for confidentiality of network communications.

Licensing As RC6 was not selected for the AES, it was not guaranteed that RC6 is royalty-free. As of January 2017, a web page on the official web site of the designers of RC6, RSA Laboratories, states the following:

"We emphasize that if RC6 is selected for the AES, RSA Security will not require any licensing or royalty payments for products using the algorithm". The emphasis on the word "if" suggests that RSA Security Inc. may have required licensing and royalty payments for any products using the RC6 algorithm. RC6 was a patented encryption algorithm (U.S. patent 5,724,428 and U.S. patent 5,835,600); however, the patents expired between 2015 and 2017.

References

Bibliography

External links "Cryptography - 256 bit Ciphers: Reference source code and submissions to international cryptographic designs contests". "Symmetric Ciphers: RC6". Standard Cryptographic Algorithm Naming (SCAN). 2009-04-15. "RC6® Block Cipher". RSA Laboratories. Archived from the original on 2016-03-04.

Illustrations

Worked examples

Example 1 — a first encounter with RC6

Start with the simplest possible case. Write down what RC6 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 RC6 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 RC6 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 RC6

In research: RC6 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 RC6 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: RC6 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Block ciphers, so understanding it makes those chapters shorter.
In everyday life: Look for RC6 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 RC6 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what RC6 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 RC6 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is RC6 in simple terms?

Why does RC6 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 RC6?

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 RC6.

RC6