In 1980, he returned to Israel, joining the faculty of
Mathematics and
Computer Science at the
Weizmann Institute. Starting from 2006, he is also an invited professor at
École Normale Supérieure in Paris. In addition to
RSA, Shamir's other numerous inventions and contributions to cryptography include the
Shamir secret sharing scheme, the breaking of the
Merkle-Hellman knapsack cryptosystem,
visual cryptography, and the
TWIRL and
TWINKLE factoring devices. Together with
Eli Biham, he discovered
differential cryptanalysis in the late 1980s, a general method for attacking
block ciphers. It later emerged that differential cryptanalysis was already known — and kept a secret — by both
IBM and the
National Security Agency (NSA). Shamir has also made contributions to computer science outside of cryptography, such as finding the first
linear time algorithm for
2-satisfiability and showing the equivalence of the
complexity classes PSPACE and
IP. ==Awards and recognition ==