An Algebraic Approach to NTRU (q = 2~n) via Witt Vectors and Overdetermined Systems of Nonlinear Equations

摘要

We use the theory of Witt vectors to develop an algebraic approach for studying the NTRU primitive with q parameter equal to a power of two. This results in a system of nonlinear algebraic equations over F_2 having many symmetries, which is reminiscent of the approach of Courtois, Murphy, Pieprzyk, Robshaw and others for studying the structure of block ciphers such as the AES. We study whether this approach to NTRU provides any immediate security threat and conclude that under the most favourable assumptions, the method is of asymptotic interest but is completely impractical at current or likely future parameter sizes.