• Journal of the Korea Society of Computer and Information
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• v.23 no.10
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• pp.111-117
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• 2018

CHAM is a lightweight block cipher, proposed in ICISC 2017. CHAM-n/k has the n-bit block and the k-bit key, and designers recommend CHAM-64/128, CHAM-128/128, and CHAM-128/256. In this paper, we study how to make optimal software implementation of CHAM such that it has high encryption speed on CPUs with high computing power. The best performances of our CHAM implementations are 1.6 cycles/byte for CHAM-64/128, 2.3 cycles/byte for CHAM-128/128, and 3.8 cycles/byte for CHAM-128/256. The comparison with existing software implementation results for well-known block ciphers shows that our results are competitive.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.28 no.5
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• pp.1071-1078
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• 2018

Recently, a family of lightweight block ciphers CHAM that has effective performance on resource-constrained devices is proposed. The CHAM uses a stateless-on-the-fly key schedule method which can reduce the key storage areas. Furthermore, the core design of CHAM is based on ARX(Addition, Rotation and XOR) operations which can enhance the computational performance. Nevertheless, we point out that the CHAM algorithm may be vulnerable to the fault injection attack which can reveal 4 round keys and derive the secret key from them. As a simulation result, the proposed fault injection attack can extract the secret key of CHAM-128/128 block cipher using about 24 correct-faulty cipher text pairs.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.29 no.4
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• pp.709-718
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• 2019

A lightweight block cipher CHAM designed for suitability in resource-constrained environment has reasonable security level and high computational performance. Since this cipher may contain intrinsic weakness on side channel attack, it should adopt a countermeasure such as masking method. In this paper, we implement the masked CHAM cipher on 32-bit microprosessor Cortex-M3 platform to resist against side channel attack and analyze their computational performance. Based on the shortcoming of having many round functions, we apply reduced masking method to the implementation of CHAM cipher. As a result, we show that the CHAM-128/128 algorithm applied reduced masking technique requires additional operations about four times.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.30 no.6
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• pp.1217-1223
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• 2020

The Block cipher CHAM is lightweight block cipher for low-end processors, developed by National Security Research Institute from Korea. The mode of operation is necessity for efficient operation of block cipher, among them, the counter (CTR) mode has good efficiency because it is easy to implement and supporting parallel operation. In this paper, we propose the optimized implementation for block cipher CHAM-CTR. The proposed implementation can be skipped some rounds by pre-computation. Thus it has better calculating speed than existing CHAM. Also, this implementation pre-load some of round keys to registers, before entering round functions. It makes reduced 160cycles loading time for round key load. Finally, proposed implementation achieved higher performance about 6.8%, and 4.5% for fixed-key scenario, and variable-key scenario, respectively.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.28 no.3
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• pp.545-550
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• 2018

Ultra-lightweight block cipher CHAM, consisting of simple addition, rotation, and eXclusive-or operations, enables the efficient implementations over both low-end and high-end Internet of Things (IoT) platforms. In particular, the CHAM block cipher targets the enhanced computational performance for the low-end IoT platforms. In this paper, we introduce the efficient implementation techniques to minimize the memory consumption and optimize the execution timing over 8-bit AVR IoT platforms. To achieve the higher performance, we exploit the partly iterated expression and arrange the memory alignment. Furthermore, we exploit the optimal number of register and data update. Finally, we achieve the high RANK parameters including 29.9, 18.0, and 13.4 for CHAM 64/128, 128/128, and 128/256, respectively. These are the best implementation results in existing block ciphers.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.34 no.4
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• pp.629-639
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• 2024

CHAM is designed with an emphasis on encryption speed, considering that in the ISO/IEC standard block cipher operation mode, encryption functions are used more often than decryption functions. In the superscalar architecture of modern general-purpose processors, different ordering of operations can lead to different processing speeds, even if the computation configuration is the same. In this paper, we analyze the implementation efficiency and security of CHAM-like structures, which rearrange the order of operations in the ARX-based block cipher CHAM, for single-block and parallel implementations in a general-purpose processor environment. The proposed structures are at least 9.3% and at most 56.4%efficient in terms of encryption speed. The security analysis evaluates the resistance of the CHAM-like structures to differential and linear attacks. In terms of security margin, the difference is 3.4% for differential attacks and 6.8%for linear attacks, indicating that the security strength is similar compared to the efficiency difference. These results can be utilized in the design of ARX-based block ciphers.

• KIPS Transactions on Computer and Communication Systems
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• v.9 no.5
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• pp.107-112
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• 2020

Ultra-lightweight password CHAM is an algorithm with efficient addition, rotation and XOR operations on resource constrained devices. CHAM shows high computational performance, especially on IoT platforms. However, lightweight block encryption algorithms used on the Internet of Things may be vulnerable to side channel analysis. In this paper, we demonstrate the vulnerability to side channel attack by attempting a first power analysis attack against CHAM. In addition, a safe algorithm was proposed and implemented by applying a masking technique to safely defend the attack. This implementation implements an efficient and secure CHAM block cipher using the instruction set of an 8-bit AVR processor.

• Proceedings of the Korea Information Processing Society Conference
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• 2021.11a
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• pp.217-220
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• 2021

ICISC'19에서 기존 CHAM과 동일한 구조와 규격을 갖지만, 라운드 수만 증가시킨 revised CHAM이 발표되었다. CHAM은 사물인터넷에서 사용되는 저사양 프로세서에서 효율적인 구현이 가능한 특징을 갖고 있다. AVR, ARM 프로세서 상에서의 CHAM 암호 알고리즘에 대한 최적 구현은 존재하지만, 아직 RISC-V 프로세서 상에서의 CHAM 구현은 존재하지 않는다. 따라서, 본 논문에서는 RISC-V 프로세서 상에서의 Revised CHAM 알고리즘을 최초로 구현을 제안한다. CHAM 라운드 함수의 내부 구조의 일부를 생략하여 최적 구현하였다. 그리고 홀수 라운드와 짝수 라운드를 모듈별로 구현하여 필요에 따라 모듈을 호출하여 손쉽게 사용할 수 있게 하였다. 결과적으로, RISC-V 상에서 제안 기법 적용하기 전보다 제안 기법 적용 후에 12%의 속도 향상을 달성하였다.

• Proceedings of the Korea Information Processing Society Conference
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• 2020.11a
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• pp.434-437
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• 2020

블록암호는 정해진 길이의 평문을 암호화하는 암호 알고리즘으로 정해진 길이보다 더 긴 평문을 암호화하기 위해 다양한 운용모드가 제안되었다. 그 중에서 카운터 모드는 블록암호를 스트림암호 형태로 바꿔주는 모드로, 평문 대신 고정 값인 논스와 블록의 순번인 카운터를 입력 값으로 사용한다. 카운터 모드는 논스 값이 고정이기 때문에 암호 연산 중에 논스가 사용되는 부분의 다른 변수가 모두 고정 값이라면 결과가 항상 동일하다는 특성이 있다. 본 논문에서는 전술한 특성을 사용하여 카운터 모드 최적 구현을 한 블록암호에 대해 정리하며, 각각의 성능을 비교해볼 것이다. 개략적으로 AES 기존 구현물보다 약 16% ~ 32% 정도의 성능 향상을 보이고 CHAM은 약 10% ~ 13% 정도의 성능 향상을 보였다.