page = a few thoughts on cryptographic engineering – some …
url = https://blog.cryptographyengineering.com
DKIM allows providers to periodically “rotate”, or replace, the keys that they use to sign outgoing emails. The frequency of this rotation is slightly limited by the caching behavior of the DNS infrastructure, but these limits aren’t very tight. Even a big provider like Google can easily replace its signing keys at least every few weeks without disrupting email transit. This sort of key replacement is good practice in any case, and it represents part of the solution.
Attack of the week: Voice calls in LTE
I haven’t written an “ attack of the week ” post in a while, and it’s been bumming me out. This is not because there’s been a lack of attacks, but mostly because there hasn’t been an attack on something sufficiently widely-used that it can rouse me out of my blogging torpor.
The scariest attacks against SGX rely on “ speculative execution ” side channels, which can allow an attacker to extract secrets from SGX — up to and including basically all of the working memory used by an enclave. This could allow extraction of values like the seed keys used by Signal’s SVR, or the sealing keys (used to encrypt that data on disk.) Worse, these attacks have not once but twice been successful at extracting cryptographic signing keys used to perform cryptographic attestation. The most recent one was patched just a few weeks ago. These are very much live attacks, and you can bet that more will be forthcoming.
My major issue with SVR is that it’s something I basically don’t want, and don’t trust. I’m happy with Signal offering it as an option to users, as long as users are allowed to choose not to use it . Unfortunately, up until this week, Signal was not giving users that choice.
More concretely: a few weeks ago Signal began nagging users to create a PIN code. The app itself didn’t really explain well that setting this PIN would start SVR backups. Many people I spoke to said they believed that the PIN was for protecting local storage, or to protect their account from hijacking .
A few weeks ago, U.S. Attorney General William Barr joined his counterparts from the U.K. and Australia to publish an open letter addressed to Facebook. The Barr letter represents the latest salvo in an ongoing debate between law enforcement and the tech industry over the deployment of end-to-end (E2E) encryption systems — a debate that will soon be moving into Congress .
Yahoo!, post-Snowden. And in case you believe that this all ended after Snowden’s leaks, we’ve learned even more disturbing things since. For example, in 2015, Yahoo got caught installing what has been described as a “rootkit” that scanned every single email in its database for specific selectors , at the request of the U.S. government. This was so egregious that the company didn’t even tell it’s CISO, who left the next week. In fact, we know a lot more about Yahoo’s collaboration during this time period , thanks to Snowden.
Attack of the week: RC4 is kind of broken in TLS