Attaque algebrique de NTRU a l'aide des vecteurs de Witt

One improves an algebraic attack of NTRU due to Silverman, Smart and Vercauteren; the latter considered the first 2 bits of a Witt vector attached to the research of the secret key; here the first 4 bits are considered, which provides additional equations of degrees 4 and 8.Comment: 6 pages; correction of the miscalculation