In this paper
we present a new formulation
and its simpler analysis of the lattice based attack of Boneh and Durfee
for the RSA cryptography [BD00].
We follow the same approach of Boneh and Durfee,
however we propose
a new way of defining a lattice
with which we can achieve the same solvable key bound d<N^{0.292}.
Our lattice is represented as a lower triangle matrix,
which makes its analysis much simpler that of [BD00].
We think that
this simpler analysis would be useful
for considering applications/generalisations of this approach.
In fact,
as an example of such applications,
we give a way of attacking RSA secret key
with a certain repetitive structure.