  In this paper, we present a deterministic attack on (EC)DSA signature scheme,
providing that several signatures are known such that the corresponding
ephemeral keys share a certain amount of bits without knowing their value. By
eliminating the shared blocks of bits between the ephemeral keys, we get a
lattice of dimension equal to the number of signatures having a vector
containing the private key. We compute an upper bound for the distance of this
vector from a target vector, and next, using Kannan's enumeration algorithm, we
determine it and hence the secret key. The attack can be made highly efficient
by appropriately selecting the number of shared bits and the number of
signatures.
