Fruit-80: A Secure Ultra-Lightweight Stream Cipher for Constrained Environments

Area of Science:

• Cryptography
• Computer Science
• Information Security

Background:

• The Sprout stream cipher, introduced in 2015, had security vulnerabilities.
• An improved version of Sprout was presented in 2017.
• The Fruit stream cipher was informally introduced in 2016, with its core structure proving resistant to cryptanalysis.

Purpose of the Study:

• To present Fruit-80, a final, secure, and easier-to-implement version of the Fruit stream cipher.
• To address the challenges of designing ultra-lightweight stream ciphers, particularly resistance to time-memory-data tradeoff (TMDTO) attacks.
• To introduce new design ideas for stream ciphers, focusing on small internal states and efficient hardware implementation.

Main Methods:

• Design of Fruit-80 with an 80-bit internal state (LFSR and NFSR) for an 80-bit security level.
• Incorporation of new design strategies to ensure resistance against TMDTO attacks, requiring an internal state at least twice the security level.
• Development of countermeasures against TMDTO distinguishing attacks.

Main Results:

• Fruit-80 is presented as a secure and easily implementable stream cipher.
• The cipher utilizes an 80-bit internal state, balancing security with lightweight requirements.
• Fruit-80 demonstrates superior initialization speed and smaller hardware area size compared to other small-state stream ciphers.
• The proposed design ideas have the potential to significantly reduce the area size of existing stream ciphers.

Conclusions:

• Fruit-80 offers a secure and efficient solution for ultra-lightweight stream cipher applications.
• The design effectively mitigates TMDTO distinguishing attacks, a key challenge in lightweight cryptography.
• The novel design principles employed in Fruit-80 can be applied to redesign other stream ciphers for improved hardware efficiency.