Technical reports

Fragment-template power-analysis attacks against microcontroller implementations of the 32-bit stream cipher ChaCha

Henry Batchelor

July 2024, 59 pages

This technical report is based on a dissertation submitted May 2024 by the author for the degree of Master of Engineering (Computer Science Tripos) to the University of Cambridge, Selwyn College.

Abstract

ChaCha is a widely adopted stream cipher, used for both random number generation and encryption. I propose a factor graph of ChaCha to improve the success rate of side-channel attacks that provide leakages throughout the entire execution of the algorithm. I also assess (fragment) template attacks against several implementations of ChaCha to demonstrate that the factor graph is helpful when working with actual side-channel attacks.

These attacks could fully recover the correct key from an 8-bit implementation. In contrast, a 32-bit implementation, with most of the state held in registers, was significantly more challenging to attack. An adversary with access to 10 power traces and an incremented counter could achieve a success rate of 14.6%. For a 32-bit implementation, with lots of SRAM activity, an attacker could successfully recover the key in 2.6% of cases from a single trace.

Full text

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BibTeX record

@TechReport{UCAM-CL-TR-995,
  author =	 {Batchelor, Henry},
  title = 	 {{Fragment-template power-analysis attacks against
         	   microcontroller implementations of the 32-bit stream cipher
         	   ChaCha}},
  year = 	 2024,
  month = 	 jul,
  url = 	 {https://www.cl.cam.ac.uk/techreports/UCAM-CL-TR-995.pdf},
  institution =  {University of Cambridge, Computer Laboratory},
  doi = 	 {10.48456/tr-995},
  number = 	 {UCAM-CL-TR-995}
}