LEA (cipher)

Key takeaways

LEA (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 LEA (cipher) to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of LEA (cipher) from memory before moving on to harder problems.

Reference excerpt

The Lightweight Encryption Algorithm (also known as LEA) is a 128-bit block cipher developed by South Korea in 2013 to provide confidentiality in high-speed environments such as big data and cloud computing, as well as lightweight environments such as IoT devices and mobile devices. LEA has three different key lengths: 128, 192, and 256 bits. LEA encrypts data about 1.5 to 2 times faster than AES, the most widely used block cipher in various software environments. LEA is one of the cryptographic algorithms approved by the Korean Cryptographic Module Validation Program (KCMVP) and is the national standard of Republic of Korea (KS X 3246). LEA is included in the ISO/IEC 29192-2:2019 standard (Information security - Lightweight cryptography - Part 2: Block ciphers).

Specification The block cipher LEA consisting of ARX operations (modular Addition: ⊞ {\displaystyle \boxplus } , bitwise Rotation: ⋘ {\displaystyle \lll } , ⋙ {\displaystyle \ggg } , and bitwise XOR ⊕ {\displaystyle \oplus } ) for 32-bit words processes data blocks of 128 bits and has three different key lengths: 128, 192, and 256 bits. LEA with a 128-bit key, LEA with a 192-bit key, and LEA with a 256-bit key are referred to as “LEA-128”, “LEA-192”, and “LEA-256”, respectively. The number of rounds is 24 for LEA-128, 28 for LEA-192, and 32 for LEA-256.

Encryption Let P = P [ 0 ] ‖ P [ 1 ] ‖ P [ 2 ] ‖ P [ 3 ] {\displaystyle P=P[0]\|P[1]\|P[2]\|P[3]} be a 128-bit block of plaintext and C = C [ 0 ] ‖ C [ 1 ] ‖ C [ 2 ] ‖ C [ 3 ] {\displaystyle C=C[0]\|C[1]\|C[2]\|C[3]} be a 128-bit block of ciphertext, where P [ i ] {\displaystyle P[i]} and C [ i ] {\displaystyle C[i]} ( 0 ≤ i < 4 {\displaystyle 0\leq i<4} ) are 32-bit blocks. Let K i = K i [ 0 ] ‖ K i [ 1 ] ‖ K i [ 2 ] ‖ K i [ 3 ] ‖ K i [ 4 ] ‖ K i [ 5 ] {\displaystyle K_{i}=K_{i}[0]\|K_{i}[1]\|K_{i}[2]\|K_{i}[3]\|K_{i}[4]\|K_{i}[5]} ( 0 ≤ i < N r {\displaystyle 0\leq i<Nr} ) be 192-bit round keys, where K i [ j ] {\displaystyle K_{i}[j]} ( 0 ≤ j < 6 {\displaystyle 0\leq j<6} ) are 32-bit blocks. Here N r {\displaystyle Nr} is the number of rounds for the LEA algorithm. The encryption operation is described as follows:

X 0 [ 0 ] ‖ X 0 [ 1 ] ‖ X 0 [ 2 ] ‖ X 0 [ 3 ] ← P [ 0 ] ‖ P [ 1 ] ‖ P [ 2 ] ‖ P [ 3 ] {\displaystyle X_{0}[0]\|X_{0}[1]\|X_{0}[2]\|X_{0}[3]\leftarrow P[0]\|P[1]\|P[2]\|P[3]}

for i = 0 {\displaystyle i=0} to N r − 1 {\displaystyle Nr-1}

X i + 1 [ 0 ] ← ( ( X i [ 0 ] ⊕ K i [ 0 ] ) ⊞ ( X i [ 1 ] ⊕ K i [ 1 ] ) ) ⋘ 9 {\displaystyle X_{i+1}[0]\leftarrow \left(\left(X_{i}[0]\oplus K_{i}[0]\right)\boxplus \left(X_{i}[1]\oplus K_{i}[1]\right)\right)\lll 9}

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with LEA (cipher)

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

In research: LEA (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 LEA (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: LEA (cipher) 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 LEA (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.

How to study LEA (cipher) in 20 minutes

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

Frequently asked questions

What is LEA (cipher) in simple terms?

The Lightweight Encryption Algorithm (also known as LEA) is a 128-bit block cipher developed by South Korea in 2013 to provide confidentiality in high-speed environments such as big data and cloud computing, as well as lightweight environments such as IoT devices and mobile devices. LEA has three d…

Why does LEA (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 LEA (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 LEA (cipher).