ITM 820 Lecture Notes - Lecture 2: Symmetric-Key Algorithm, Message Authentication, Ciphertext

• School: Ryerson University
• Department: Information Technology Management
• Course: ITM 820
• Professor: Nurul Huda

Document Summary

It(cid:859)s the u(cid:374)i(cid:448)e(cid:396)sal te(cid:272)h(cid:374)i(cid:395)ue fo(cid:396) p(cid:396)o(cid:448)idi(cid:374)g (cid:272)o(cid:374)fide(cid:374)tialit(cid:455) fo(cid:396) t(cid:396)a(cid:374)s(cid:373)itted o(cid:396) sto(cid:396)ed data. The exact substitutions and transformations performed by the algorithm depend on the key: ciphertext is the scrambled message produced as output. It depends on the plaintext and secret key. For a given message, 2 diff. keys will produce 2 diff. ciphertexts: decryption algorithm takes the ciphertext and secret key and produces the plaintext. The one-time pad: he(cid:396)e the ke(cid:455) does(cid:374)(cid:859)t (cid:396)epeat itself, the le(cid:374)gth of plai(cid:374)te(cid:454)t e(cid:395)uals the le(cid:374)gth of the ke(cid:455), every plaintext will have one ciphertext, example: plain = heilhitler, key = wclnbtdefj, cipher = dgtyibwpja. Message authentication: encryption protects against passive attack (eavesdropping). To protect against active attacks (falsification), we use message or data authentication: message authentication is a procedure that verifies if a received message is authentic. It (cid:448)e(cid:396)ifies if the (cid:373)essage has(cid:374)(cid:859)t (cid:271)ee(cid:374) alte(cid:396)ed, if it(cid:859)s f(cid:396)o(cid:373) a(cid:374) authe(cid:374)ti(cid:272) sou(cid:396)(cid:272)e, a(cid:374)d (cid:448)e(cid:396)ifies if it(cid:859)s i(cid:374) a ti(cid:373)el(cid:455) a(cid:374)d (cid:272)o(cid:396)(cid:396)e(cid:272)t se(cid:395)ue(cid:374)(cid:272)e.