science

ICE (cipher)

ICE (cipher) 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 ICE (cipher) rather than just read about it. In short: In cryptography, ICE (Information Concealment Engine) is a symmetric-key block cipher published by Matthew 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.

Key takeaways

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

Reference excerpt

In cryptography, ICE (Information Concealment Engine) is a symmetric-key block cipher published by Matthew 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. The ICE algorithm is not subject to patents, and the source code has been placed into the public domain. ICE is a Feistel network with a block size of 64 bits. The standard ICE algorithm takes a 64-bit key and has 16 rounds. A fast variant, Thin-ICE, uses only 8 rounds. An open-ended variant, ICE-n, uses 16n rounds with 64n bit key. Van Rompay et al. (1998) attempted to apply differential cryptanalysis to ICE. They described an attack on Thin-ICE which recovers the secret key using 223 chosen plaintexts with a 25% success probability. If 227 chosen plaintexts are used, the probability can be improved to 95%. For the standard version of ICE, an attack on 15 out of 16 rounds was found, requiring 256 work and at most 256 chosen plaintexts.

Structure ICE is a 16-round Feistel network. Each round uses a 32→32 bit F function, which uses 60 bits of key material. The structure of the F function is somewhat similar to DES: The input is expanded by taking overlapping fields, the expanded input is XORed with a key, and the result is fed to a number of reducing S-boxes which undo the expansion. First, ICE divides the input into 4 overlapping 10-bit values. They are bits 30, 31 and 0–7 of the input for the first 10-bit value and for the next values 6–15, 14–23, and 22–31. Second is a keyed permutation, which is unique to ICE. Using a 20-bit permutation subkey, bits are swapped between halves of the 40-bit expanded input. (If subkey bit i is 1, then bits i and i+20 are swapped.) Third, the 40-bit value is XORed with 40 more subkey bits. Fourth, the value is fed through 4 10-bit S-boxes, each of which produces 8 bits of output. (These are much larger than DES's 8 6→4 bit S-boxes.) Fifth, the S-box output bits are permuted so that each S-box's outputs are routed to each 4-bit field of 32-bit word, including 2 of the 8 "overlap" bits duplicated during the next round's expansion. Like DES, a software implementation would typically store the S-boxes pre-permuted, in 4 1024×32 bit lookup tables.

References Matthew Kwan, The Design of the ICE Encryption Algorithm, Fast Software Encryption 1997, pp. 69–82 [1]. Bart van Rompay, Lars R. Knudsen and Vincent Rijmen, Differential Cryptanalysis of the ICE Encryption Algorithm, Fast Software Encryption 1998, pp270–283 (PDF).

External links The ICE Home Page The ICE information slides

Illustrations

Worked examples

Example 1 — a first encounter with ICE (cipher)

Start with the simplest possible case. Write down what ICE (cipher) 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 ICE (cipher) 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 ICE (cipher) 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 ICE (cipher)

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

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

Frequently asked questions

What is ICE (cipher) in simple terms?

Why does ICE (cipher) 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 ICE (cipher)?

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 ICE (cipher).