Browser cryptography is an evolving field. What was secure yesterday may not be secure today since both malicious actors and security researchers are looking for ways to break new encryption techniques or discover flaws in older algorithms. That’s the case with SHA-1 certificates: While theoretically broken for more than a decade, it’s only recently the cost of a collision attack became something most cybercrime groups and government agencies could afford.
Big browsers have committed to rejecting these certs by the start of 2017. But according to SC Magazine, Mozilla now is talking about moving up the timeline because costs keep falling and the chances of a malicious attack are rising. By June 2016, SHA-1 may be sidelined.
Much of the work done on SHA-1 came form security researcher Bruce Schneier. In 2012, he predicted that the cost of creating a collision attack — which forces two inputs to produce the same hash, giving attackers the ability to swap out benign functions for malicious content — would be $700,000 in 2015 but could quickly fall to just $143,000 by 2018. That meant SHA-1 collisions as a practical form of attack were at least three years away.
As reported by ZDNet, however, new data suggested that the price of collision is already down in the $120,000 range, and possibly as low as $75,000. Using a freestart collision model on a 64-GPU Kraken cluster, researchers found that it took only a few months to achieve a successful hack. More worrisome is that nearly 1 million websites still use signed SHA-1 certificates, giving cybercriminals ample attack surface once they’re able to front the (steadily falling) cost of needed compute power.
According to CSO Online, there’s already a consensus among major browser-makers and certificate authorities (CAs) that the time of SHA-1 is over. The CA/Browser Forum has decided that new SHA-1 certs should not be issued after Jan. 1, 2016, while browser-makers agreed that a year later — Jan. 1, 2017 — these certificates will no longer be trusted even if their end date extends past the January cutoff. Now, Mozilla is talking about moving up the cutoff date by six months, meaning that by July 1, 2016, SHA-1 could be on the outs.
Thomas Peyrin of Nanyang Technological University, one of the researchers who demonstrated the new risk of SHA-1 collisions, argued the tech industry should “accelerate the migration process toward SHA-2 and SHA-3 before such dramatic attacks become feasible.” And while there’s no doubt a Mozilla decision to move up the cutoff date would cause some inconvenience, the CA/Browser Forum seems to be backing the idea since it just withdrew a proposal from several major players to keep SHA-1 certs valid throughout 2016. With 24 percent of the top HTTPS websites still using the compromised certs, this is probably a good idea.
SHA-1 is out, and SHA-2 and 3 are in development. The cost of a collision attack is down — way down — and Mozilla wants to step up. Time will tell if security or simplicity carries the day.