his M. Sc. thesis is based on the following papers: • Joux Antoine, “A new index calculus algorithm with complexity L(?/? amp;#??; o(?)) in very small characteristic”, Selected Areas in Cryptography–SAC ????, vol. ????, Springer, pp ???-???, ????. • Barbulescu Razvan, Gaudry Pierrick, Joux Antoine, Thomé Emmanuel, “A quasi-polynomial algorithm for discrete logarithm in finite fields of small characteristic”, Advances in Cryptology EUROCRYPT ????, vol. ????, Springer pp. ?-??, ????. Revealing transmitted messages between two communication parties could lead to Irreparable consequences. Therefore it is necessary to invent some procedures for concealing the content of communications.
