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SIT: A Lightweight Encryption Algorithm for Secure Internet of Things
Muhammad Usman, Irfan Ahmed, M. Imran Aslam, Shujaat Khan, Usman Ali Shah
TL;DR
IoT requires secure communication and data handling, but its devices have limited energy and computational capability, making conventional encryption costly. The paper proposes SIT, a lightweight 64-bit block cipher combining Feistel and substitution-permutation structures, and reports security results from five encryption rounds.
Problem
IoT devices must protect data confidentiality, integrity, and authenticity despite limited energy and computational capability that constrain conventional encryption.
Method
The paper proposes SIT, a lightweight symmetric 64-bit block cipher using a 64-bit key, five rounds, and a hybrid Feistel and substitution-permutation architecture.
Results
49% of cipher bits change after a single-bit key or plaintext change, close to the ideal 50% avalanche change.
Takeaways & Limitations
The implementation shows promising results, making SIT a suitable candidate for adoption in IoT applications.
Abstract
from arXiv · showhide
The Internet of Things (IoT) being a promising technology of the future is expected to connect billions of devices. The increased number of communication is expected to generate mountains of data and the security of data can be a threat. The devices in the architecture are essentially smaller in size and low powered. Conventional encryption algorithms are generally computationally expensive due to their complexity and requires many rounds to encrypt, essentially wasting the constrained energy of the gadgets. Less complex algorithm, however, may compromise the desired integrity. In this paper we propose a lightweight encryption algorithm named as Secure IoT (SIT). It is a 64-bit block cipher and requires 64-bit key to encrypt the data. The architecture of the algorithm is a mixture of feistel and a uniform substitution-permutation network. Simulations result shows the algorithm provides substantial security in just five encryption rounds. The hardware implementation of the algorithm is done on a low cost 8-bit micro-controller and the results of code size, memory utilization and encryption/decryption execution cycles are compared with benchmark encryption algorithms. The MATLAB code for relevant simulations is available online at https://goo.gl/Uw7E0W.
I. INTRODUCTION
IoT connects physical devices that sense, communicate, and share data, but its scale and resource constraints create significant security and privacy challenges. Lightweight protection is needed to preserve confidentiality, integrity, and authenticity without overburdening constrained devices.
- I. INTRODUCTION: IoT connects ordinary physical entities that sense, communicate with other devices, and transmit data to integrated platforms.The platform integrates data from many devices and applies analytics for applications.
- I. INTRODUCTION: IoT security must protect confidentiality, data integrity, and authenticity as devices share large amounts of valuable data.The paper frames these properties as concerns arising from IoT security and privacy requirements.
- I. INTRODUCTION: 50 billion objects were estimated to be connected to the Internet by 2020, increasing the scale of data and communication.The estimate corresponds to approximately 6.6 connected objects per person.
- I. INTRODUCTION: IoT components are exposed to physical attacks, wireless eavesdropping, and resource limitations in energy and computational capability.Unsupervised components increase physical-attack exposure, while wireless communication makes eavesdropping simple.
- I. INTRODUCTION: Computationally expensive conventional security algorithms can hinder the performance of energy-constrained IoT devices.The paper identifies constrained energy and computation as barriers to deploying conventional cryptography.
C. Motivation And Organization of Paper
The paper motivates a security-efficiency trade-off for IoT hardware and proposes SIT as a lightweight cryptographic response. It positions the algorithm within prior lightweight-cipher research and evaluates its resource implications against existing approaches.
- C. Motivation And Organization of Paper: 70% of IoT devices were reported as vulnerable to attacks, underscoring the need for security mechanisms during storage and transmission.The paper also identifies man-in-the-middle attacks and data-integrity concerns as relevant threats.
- C. Motivation And Organization of Paper: SIT is proposed as a lightweight cryptographic algorithm designed to address IoT security and resource-utilization challenges.The paper organizes its presentation around related work, algorithm architecture, evaluation, and conclusions.
- Related Work: Existing lightweight ciphers do not always exploit security-efficiency trade-offs, while block ciphers are reported to offer comparatively better performance.The related work covers block ciphers, stream ciphers, and hash functions.
- Related Work: AES key size affects encryption, decryption, and key-setup execution, whereas XXTEA and Skipjack use less energy but provide lower security strength than AES and RC5.These comparisons were conducted on constrained hardware platforms using measurements of energy consumption, memory utilization, and execution time.
- Related Work: RC5 execution time increases with word size, illustrating how cipher parameters influence resource costs on constrained hardware.RC5 permits variation in key size, round count, and word size.
III. PROPOSED ALGORITHM
SIT combines Feistel and substitution-permutation structures in a lightweight 64-bit block cipher designed for IoT. Its five-round design uses compact transformations and key expansion to provide security while moderating computational complexity.
- III. PROPOSED ALGORITHM: SIT combines Feistel and substitution-permutation networks to provide confusion and diffusion with moderate computational complexity.The hybrid architecture also retains the near-identical encryption and decryption operations associated with Feistel designs.
- III. PROPOSED ALGORITHM: Five encryption rounds replace the typical 10 to 20 rounds, while each round operates on 4-bit data segments.The design targets improved energy efficiency for constrained IoT devices while maintaining confusion and diffusion through substitution-diffusion functions.
- A. Key Expansion: 64-bit cipher keys are expanded into five unique round keys required by the five-round encryption and decryption process.The 64-bit input key is divided into 4-bit segments, processed through four f-function blocks, and transformed into round keys.
- A. Key Expansion: The f-function uses P and Q tables for linear and nonlinear transformations that produce confusion and diffusion.The key-expansion architecture uses an f-function influenced by a tweaked Khazad block cipher.
- A. Key Expansion: Four 16-bit arrays are arranged as K1, K2, K3, and K4, then XORed to obtain the fifth key.The supplied key-expansion description specifies the bit arrangements for each of the first four round keys and the XOR operation for the fifth.
B. Encryption
SIT encrypts 64-bit plaintext through repeated rounds that combine segmentation, XNOR, substitution, swapping, and XOR operations before concatenating the final segments into ciphertext.
- 64-bit plaintext is divided into four 16-bit segments before the first encryption round.
- Each round applies bitwise XNOR with the round key to the first and fourth segments, then feeds the outputs into the f-function.
- The encryption f-function uses swapping and substitution, followed by XOR operations that combine its outputs with the second and third segments.
- Round transformation swaps the resulting segments so each succeeding round receives them in a changed order.
- The same steps are repeated for the remaining rounds, and the final results are concatenated to produce ciphertext.
IV. SECURITY ANALYSIS
The security analysis assumes an attacker can access transmitted data and relates SIT's security to existing analyses of its Feistel and uniform substitution-combination components.
- The security model assumes the attacker has complete access to information transmitted through the channel.
- SIT's combination of Feistel and uniform substitution-combination structures allows the analysis to draw on existing security analyses of those primitives.
A. Linear and Differential Cryptanalysis
The f-function is designed using a transformation whose reported cryptanalysis finds no successful differential or linear attacks against the complete cipher, while uniform round processing supports resistance to differential attacks.
- Cryptanalysis of the f-function's source reports that differential and linear attacks do not succeed against the complete cipher.
- Linear approximation across two rounds produces very large input-output correlation.
- The uniform round transformation treats every bit similarly and provides opposition to differential attacks.
B. Weak Keys
SIT avoids making nonlinear operations depend on the actual key value by XORing first and using fixed nonlinearity in the f-function.
- Dependence of nonlinear operations on the actual key value can create detectable weakness in a block cipher.
- SIT first XORs the input with the key and then applies an f-function whose nonlinearity is fixed.
- Because the f-function's nonlinearity is fixed, the algorithm imposes no limitation on key selection.
C. Related Keys
SIT addresses related-key and structural attacks through nonlinear key expansion, diffusion, and an S-box/diffusion-layer design. The evaluation includes key sensitivity and avalanche testing.
- SIT’s key expansion is designed for fast, nonlinear diffusion of key differences into round keys.
- The proposed S-box and diffusion layer make rational-expression attacks based on simple cipher structures impracticable.
- 2^8 key guesses using 2^8 plaintexts recover one byte of the last key, requiring 2^16 S-box lookups.
- Security testing evaluates key sensitivity, avalanche behavior, image statistics, and computational resource utilization.
- A one-bit key or plaintext change is assessed through the avalanche test, where 50% changed bits represents the ideal SAC result.
2) Execution Time:
The evaluation examines whether SIT provides secure image transformation while remaining suitable for resource-constrained IoT devices. It measures randomness, correlation, execution time, and memory use.
- Execution Time: SIT’s execution time is treated as a fundamental criterion because IoT devices require minimal processing time alongside security.
- Memory Utilization: Memory utilization is evaluated because computational rounds can occupy significant memory on constrained IoT devices.
- Histogram: A uniform encrypted-image histogram is interpreted as an indication of appreciable security.
- Entropy: Image entropy measures the amount of information, with higher entropy described as better security performance.
- Correlation: Correlation testing assesses dependency between original and encrypted images, with an ideal cipher coefficient γ = 0 and worst case γ = 1.
- Correlation: The correlation coefficient uses covariance normalized by the variances of variables x and y.
- Correlation: The covariance formulation is obtained by transforming the variance expression, with cov(x, y) denoting covariance between x and y.
B. Results
SIT is evaluated through hardware measurements and image-based security tests. The reported results indicate near-ideal avalanche behavior, near-maximum encrypted-image entropy, and weak encrypted-image correlation.
- 0.188 milliseconds encryption and 0.187 milliseconds decryption execution times are reported for SIT on an ATmega 328 platform.The implementation uses an Arduino Uno board and reports 22 bytes of memory utilization.
- Hardware implementation results are compared with other algorithms in Table IV.The table reports block and key sizes in bits, code and RAM in bytes, and cycles including key expansion, encryption, and decryption.
- 49% of cipher bits change after a single key or plaintext bit change, close to the ideal 50% avalanche result.
- Encrypted images have entropy close to the 8-bit maximum across the tested grayscale images.
- Encrypted images show little apparent correlation, contrasting with the high correlation observed in original images.
- Table V presents results for correlation and entropy.
VI. FUTURE WORK
Future work targets broader implementation and optimization of SIT across hardware and software environments. The authors also propose exploring FPGA throughput and adjustable rounds, architectures, and key lengths.
- Future research will implement SIT across various computation and network environments.
- The algorithm may be optimized for improved performance on different hardware platforms.
- FPGA implementation is expected to provide high throughput through parallel code execution.
- Scalability may be explored by changing the number of rounds, architecture, or supported key length.
- The conclusion calls for detailed performance evaluation and cryptanalysis on different hardware and software platforms for possible attacks.