<HTML><BODY><div> <div class="js-helper js-readmsg-msg"><style type="text/css"></style><div><div id="style_16004134610021501982_BODY"><div class="cl_443492"><div><div class="js-helper_mr_css_attr js-readmsg-msg_mr_css_attr"><div><div id="style_16003755070463928171_BODY_mr_css_attr"><div class="cl_418772_mr_css_attr"><div><div class="js-helper_mr_css_attr_mr_css_attr js-readmsg-msg_mr_css_attr_mr_css_attr"><div><div id="style_16003752480099088103_BODY_mr_css_attr_mr_css_attr"><div class="cl_417290_mr_css_attr_mr_css_attr"><div><div class="js-helper_mr_css_attr_mr_css_attr_mr_css_attr js-readmsg-msg_mr_css_attr_mr_css_attr_mr_css_attr"><div><div id="style_16003750930556135926_BODY_mr_css_attr_mr_css_attr_mr_css_attr"><div class="cl_417155_mr_css_attr_mr_css_attr_mr_css_attr"><div><div class="js-helper_mr_css_attr_mr_css_attr_mr_css_attr_mr_css_attr js-readmsg-msg_mr_css_attr_mr_css_attr_mr_css_attr_mr_css_attr"><div><div id="style_16003609440700503826_BODY_mr_css_attr_mr_css_attr_mr_css_attr_mr_css_attr"><div class="cl_416652_mr_css_attr_mr_css_attr_mr_css_attr_mr_css_attr"><div>Good afternoon!<br>I with my friends-students got a task to investigate ciphering algorithm GEA3, using in GPRS/EDGE.</div><div>While communication MS and Osmocom base station (BS) we've got the LLC-message:</div><div>LLC MESSAGE (ciphered): 01C00F1840623297A594EE196714A2653D23D5A2AC52792F0434</div><div>with the following parameters:</div><div>Cipher Algorithm: GEA3<br>Kc_GPRS: A8FC3A996A80D000<br>SAPI: 1 <br>NU: 3 <br>IOV_UI: 0 <br>OC: 0 </div><div>After applying algorithm GEA3 we've got deciphered LLC-message:</div><div>LLC MESSAGE (deciphered): 01C00F0802012A0452F00300010017161805F4D7BF04CA 26176B<br> <br>We get, calculated FCS (6B1726) using deciphered LLC-message and contained in LLC-message FCS (6B1726) are equal.</div><div> </div><div>While communication MS and the real BS we've got the following LLC-message:</div><div>LLC MESSAGE (ciphered) 41C00B9299A1EB51A1AD1FE71633786B23CBD8E6D41C9F658C89C9544AF2BAAC35</div><div>with the following parameters:</div><div>Cipher Algorithm: GEA3<br>KC_GPRS: 8f94a69c3d9bdf48<br>SAPI: 1<br>NU: 2<br>IOV_UI: 0x10000000 (got from XID)<br>OC: from 0 to <span class="js-phone-number_mr_css_attr_mr_css_attr_mr_css_attr_mr_css_attr"><span class="js-phone-number_mr_css_attr_mr_css_attr_mr_css_attr"><span class="js-phone-number_mr_css_attr_mr_css_attr"><span class="js-phone-number_mr_css_attr"><span class="js-phone-number">8388608</span></span></span></span></span></div><div>So we tried to apply the OC parameter from 0 to <span class="js-phone-number_mr_css_attr_mr_css_attr_mr_css_attr_mr_css_attr"><span class="js-phone-number_mr_css_attr_mr_css_attr_mr_css_attr"><span class="js-phone-number_mr_css_attr_mr_css_attr"><span class="js-phone-number_mr_css_attr"><span class="js-phone-number">8388608</span></span></span></span></span> to decipher the message (other parameters were not been changed).<br>In every step, we calculated FCS and compared it with contained in LLC-message FCS and had no success.</div><div>Finally the question:<br>Can the value of IOV_UI (Osmocom BS: 0, real BS: 0x10000000) affect the deciphering, and if yes then how??</div><div>With regards, students of the telecommunication department.</div><div><br>Thank you for your attention!</div><div> </div><div>Best regards, Sergei</div></div></div></div></div></div></div></div></div></div><div> </div></div><style type="text/css"></style><style type="text/css"></style></div></div></div></div><div> </div></div></div></div></div></div></div></div></div></div></div><hr><div> </div> <div> </div></div><style type="text/css"></style><style type="text/css"></style><style type="text/css"></style></BODY></HTML>