<div dir="ltr">It appears Ofek got the help he needed here.<br><a href="https://github.com/pyca/cryptography/pull/3287">https://github.com/pyca/cryptography/pull/3287</a><br><br><div class="gmail_quote"><div dir="ltr">On Sat, Dec 3, 2016 at 6:08 PM Ofek Lev <<a href="mailto:ofekmeister@gmail.com">ofekmeister@gmail.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr" class="gmail_msg"><div style="font-size:12.8px" class="gmail_msg">I understand for prime curves it is just `bytes(0x02 + flag) + bytes(x)` where flag is the LSB of y. For the F2m curves I cannot make out how to do it.</div><div style="font-size:12.8px" class="gmail_msg"><br class="gmail_msg"></div><div style="font-size:12.8px" class="gmail_msg"><a href="http://grouper.ieee.org/groups/1363/IBC/material/P1363.3-D1-200805.pdf%20section%205.6.6.1.2" class="gmail_msg" target="_blank">IEEE P1363</a> section 5.6.6.1.2 appears to say flag is '1 if y of point > y of inverse point else 0' which I think just means `if y > x`.<br class="gmail_msg"></div><div style="font-size:12.8px" class="gmail_msg"><br class="gmail_msg"></div><div style="font-size:12.8px" class="gmail_msg"><a href="http://cs.ucsb.edu/~koc/ccs130h/projects/03-ecc-protocols/Julio_Slides.pdf" class="gmail_msg" target="_blank">these slides</a> (slide 15) by Julio Lopez and Ricardo Dahab appear to suggest my interpretation of the IEEE method is off (I think).<br class="gmail_msg"></div><div style="font-size:12.8px" class="gmail_msg"><br class="gmail_msg"></div><div style="font-size:12.8px" class="gmail_msg"><a href="http://www.secg.org/sec1-v2.pdf%20section%202.3.3%20part%202.2.2" class="gmail_msg" target="_blank">http://www.secg.org/sec1-v2.pdf</a> (which I think is the standard reference) section 2.3.3 part 2.2.2 has yet another notation that I do not understand.<br class="gmail_msg"></div><div style="font-size:12.8px" class="gmail_msg"><br class="gmail_msg"></div><div style="font-size:12.8px" class="gmail_msg">I was told there are multiple ways. Can someone please explain the most *standard* (or easiest) way requiring size <span style="font-size:12.8px" class="gmail_msg">m + 1</span><span style="font-size:12.8px" class="gmail_msg">, preferably from a programmer's perspective? This math is beyond me :)</span></div><div style="font-size:12.8px" class="gmail_msg"><br class="gmail_msg"></div><div style="font-size:12.8px" class="gmail_msg">Any insight would be greatly appreciated.</div></div>
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