<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class=""><br class=""><div><br class=""><blockquote type="cite" class=""><div class="">On Oct 31, 2018, at 3:03 PM, <a href="mailto:jamesd@echeque.com" class="">jamesd@echeque.com</a> wrote:</div><br class="Apple-interchange-newline"><div class=""><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;" class="">Launching a birthday attack on a </span></div></blockquote>perfectly secure<br class=""><blockquote type="cite" class=""><div class=""><span style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none; float: none; display: inline !important;" class="">128 bit hash would involve generating 2^64 hashes and sorting them. This requires 3*2^67 bytes of disk. The largest readily available hard disk is 16 terabytes, so this would require thirty million hard disks, which is only a concern for state level attacks on very high value targets, although with continued progress in hard disks, will come within range for normal attackers, but only if a birthday attack generates major value for the attacker.</span><br style="caret-color: rgb(0, 0, 0); font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration: none;" class=""></div></blockquote></div><br class=""><div class="">If you can guarantee that the hash is secure, sure. Running “at the edge” of security seems to be a dangerous thing to do. </div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span><a href="https://link.springer.com/content/pdf/10.1007/978-3-540-72540-4_1.pdf" class="">Chosen-prefix collisions for MD5 and colliding X. 509 certificates for different identities</a></div></body></html>