Klein Cipher advanced cryptography.pptx

Introduction
 Designed for resource-constrained devices like RFID, IoT, and sensors etc
 Places more emphasis on compact hardware/ software implementation
 Far lesser secure against sophisticated cryptanalysis attacks
 Proposed by Zheng Gong (University of Twente, Netherlands), Svetla Nikova (Katholieke
Universiteit Leuven, Belgium) and Yee Wei Law (The University of Melbourne, Australia) in
their publication titled ‘KLEIN: A New Family of Lightweight Block Ciphers’
 Paper was presented at IEEE Workshop at Massachusetts, Washington DC in 2011
 Still an ‘academic cipher’, not been adopted in industry or has achieved international
standardization as AES or other lightweight standards like PRESENT
Analysis - KLEIN Lightweight Block Cipher by Shahid & Mahnoor (MSIS 24)

Analysis - KLEIN Lightweight Block Cipher
Basic Parameters
Cipher Structure
Features of the Components
Security Analysis
Use Cases
Comparison with Contemporary Block Ciphers
S
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c
e

Parameters Structure Features Security Analysis Use Cases Comparison
KLEIN Cipher: 3 variants based on key size

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4

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Key Schedule
 Step 1: Division of master key in
two byte-oriented tuples
 Step 2: Cyclic left shift of one
byte in each tuple
 Step 3: Swap of tuples with
Feistel-like structure
 Step 4: Xor round counter i with
3rd
byte of the left tuple, and
substitute 2nd
and 3rd
byte of right
tuple
 Truncate left-most 64 bits for
respective round transformation

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SubNibbles
 KLEIN uses 4x4 S-Box involutive substitution, for non-linear
permutation
 Involutive S-Box saves the cost of implementation of its inverse

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Design of S-Box
Core Design Principle: Inversion in a Finite Field
 The core of KLEIN S-Box is based on mathematical operation of AES on a small scale
 AES calculates the multiplicative inverse in the finite field GF(2⁸)/ 8-bit followed by an affine
transformation
 Similarly, KLEIN calculates the multiplicative inverse in the finite field GF(2⁴)/ 4-bit followed by
a different, simpler affine transformation
Step-by-Step Construction of the KLEIN S-Box
• Step 1: Define the Finite Field GF(2⁴). KLEIN uses
P(x) = x⁴ + x + 1 (irreducible polynomial)
 Step 2: Compute the Multiplicative Inverse.
Finds an element `y` such that `x · y ≡ 1 mod P(x)`
 Step 3: Apply the Affine Transformation.
Calculates S(x) = A · x⁻¹ b
⊕
1 0 1 1 0
A = 1 1 0 1 , b = 1
1 1 1 0 1
0 1 1 1 0

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RotateNibbles
 16 nibbles will be rotated left 2 bytes
 For inverse operation, 2 bytes will be rotated right

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MixNibbles
 In this step, above equations are applied to the two tuples of state to get
intermediate state for the next round transformation
 This step is omitted in the last round
 We will get state for the next transformation round

 Confusion and Diffusion
o The SubNibble step offers ‘Confusion’ through its non-linearity, employed to confounding
the relationship between Cipher Text and Key
o RotateNibble and MixNibble steps add ‘Diffusion’ through infusing inter-byte diffusion
across rounds and employing multiplication of irreducible polynomial, respectively for
blurring the relationship between Plain and Cipher texts.
 Avalanche Effect
o Independent analyses have confirmed that after 4-6 rounds, KLEIN achieves a satisfactory
avalanche effect close to the ideal value, which validates its sound diffusion mechanism.

Known Weaknesses/ Vulnerabilities
 Weak Key Scheduling. The KeySchedule does not mix higher and lower nibbles, which helps a
reduced partial key search
 Limited Key Size. It is vulnerable to brute-force and related-key attacks, particularly as
computational capabilities advance.
 Weak Diffusion. 4-bit S-boxes utilizes an 8-bit S-box design and MixColumns inadequately
combines the higher and lower nibbles, allowing attackers to take advantage of structural
vulnerabilities
 Practical Attacks on Reduced Rounds. Analyses indicated that as many as 10 rounds of KLEIN-
64 could be susceptible to attacks prior to the completion of full-round cryptanalysis

Use Cases
 Practical Implementation. It is best suited to be used in resource-constrained systems like IoT
sensors, RFIDs, and embedded systems in smart cards, wearable devices, and other hardware
with small computational capabilities
 Research and Academic Benchmarking
o A valued case study in the design and cryptanalysis of lightweight block ciphers.
o Numerous researchers have tried hardware and software implementation of this cipher,
alongside comparison of efficiency and utility with other lightweight ciphers like PRESENT,
PICCOLO, and LBlock etc.

Any Question!

Thank You

Klein Cipher advanced cryptography.pptx

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