Méndez-Ramírez et al. / Front Inform Technol Electron Eng 2018 19(2):165-179 165 Chaotic digital cryptosystem using serial peripheral interface protocol and its dsPIC implementation * Rodrigo MÉNDEZ-RAMÍREZ 1 , Adrian ARELLANO-DELGADO 2 , César CRUZ-HERNÁNDEZ †‡1 , Fausto ABUNDIZ-PÉREZ 3 , Rigoberto MARTÍNEZ-CLARK 1 1 Electronics and Telecommunications Department, Scientific Research and Advanced Studies Center of Ensenada, Ensenada 22860, Mexico 2 CONACYT-UABC Engineering, Architecture, and Design Faculty, Autonomous University of Baja California, Ensenada 22860, Mexico 3 Engineering, Architecture and Design Faculty, Autonomous University of Baja California, Ensenada 22860, Mexico † E-mail: ccruz@cicese.mx Received June 17, 2016; Revision accepted Jan. 23, 2017; Crosschecked Feb. 15, 2018 Abstract: The current massive use of digital communications demands a secure link by using an embedded system (ES) with data encryption at the protocol level. The serial peripheral interface (SPI) protocol is commonly used by manufacturers of ESs and integrated circuits for applications in areas such as wired and wireless communications. We present the design and experimental implementation of a chaotic encryption and decryption algorithm applied to the SPI communication protocol. The design of the chaotic encryption algorithm along with its counterpart in the decryption is based on the chaotic Hénon map and two methods for blur and permute (in combination with DNA sequences). The SPI protocol is configured in 16 bits to synchronize a transmitter and a receiver considering a symmetric key. Results are experimentally proved using two low-cost dsPIC microcontrollers as ESs. The SPI digital-to-analog converter is used to process, acquire, and reconstruct confidential messages based on its properties for digital signal processing. Finally, security of the cryptogram is proved by a statistical test. The digital processing capacity of the algorithm is validated by dsPIC microcontrollers. Key words: Chaotic systems; Statistical tests; Embedded systems; dsPIC microcontroller; Serial peripheral interface (SPI) protocol https://doi.org/10.1631/FITEE.1601346 CLC number: TP309.7 1 Introduction Embedded systems (ESs) are increasingly used to develop and integrate a large number of electronic devices for wired and wireless communication applications. Depending on the application, it is more convenient and economical to use a communication protocol that allows the use of fewer communication lines and in which the transmitted information is secure (Barr and Massa, 2006). Within the commu- nication protocols there are the inter-integrated circuit (I²C) and the serial peripheral interface (SPI) proto- cols. Both are suitable for data transfer among pe- ripherals with low or medium speed for communica- tions of electronic integrated circuits (ICs). The I²C protocol was created by Philips Semiconductors (1995, 2003), and the SPI protocol was created by Motorola Inc. (2003). Both types of protocols coexist in modern digital electronic systems, and probably these protocols will continue complementing each other in the future because they are inexpensive for implementation (Oudjida et al., 2009). The SPI protocol allows communication among peripherals and electronic devices. The mode of connection between these devices can be assigned in master and slave modes. The devices are controlled, Frontiers of Information Technology & Electronic Engineering www.jzus.zju.edu.cn; engineering.cae.cn; www.springerlink.com ISSN 2095-9184 (print); ISSN 2095-9230 (online) E-mail: jzus@zju.edu.cn ‡ Corresponding author * Project supported by the CONACYT, México (No. 166654) ORCID: Rodrigo MÉNDEZ-RAMÍREZ, http://orcid.org/0000- 0002-2593-8658 © Zhejiang University and Springer-Verlag GmbH Germany, part of Springer Nature 2018