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Comment by spullara | Hacker News Reader

Encryption at rest (where the customer isn't the sole owner of the key) applies to a very dumb attack vector, disk drives found in a landfill that somehow weren't wiped and shredded as they left the DC.

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On the one hand, fair, I hadn't considered that eventuality. Still, I can't imagine a scenario where, "I need to be able to guard against [cloud provider] blobs being left unencrypted for the long-term" that doesn't also include "and protect against two of their internal services being co-compromised".

If I can't trust blobs in a landfill, I wouldn't trust blobs in a landfill that are decrypted by another blob in the same landfill. Just feels like smoke and mirrors that is purely about chasing CTOs and "CYA"-type decisions.

It's not usually landfills which are the vector for this kind of leak, it's second-hand disk sales. This includes both decommed hardware and items scavenged from failures: often the failure was transient, or in the chassis; the maintenance vendor will test and resell the disk if it passes. They are supposed to be wiped, but this takes a long time and is almost never verified so the process is often incomplete.

Some such vendors have a blanket destruction policy for old hardware, but this obviously means higher prices, so it's usually only borne by medical and military institutions. And there have been notable cases where this was supposed to happen but the disks ended up on eBay, unwiped, regardless.

SSDs make this even more likely because they have pools of storage which are screened off from normal access but are typically readable through special code in the firmware; as failing sectors are swapped out, sensitive plaintext can remain behind, unable to be wiped by a conventional dd-style blast. (HDDs have this too, but in much smaller quantities.)

I don't believe that AWS sells its retired equipment, at least I could find no evidence for it and thus I think the likelyhood that someone gets a hold of an unwiped/unshredded SSD from them to be exceedingly low.

I am surprised that drive manufacturers haven't built in encryption at rest though since it would be pretty easy to generate a key on first boot and then make it easy to wipe by just making a new key and thus essentially scrambling all the data on the disk instantly without having to wipe them at all.

That’s called a self-encrypting drive (SED) and is pretty common. It just costs more and/or is slower.

Common I think is a stretch but that is great.

Looks like this change is more to protect against Insider threats, ie Amazon employees or their infrastructure is compromised, and to make it easier to comply with some security policies that require EAR.

This doesn't protect against insider threats at all since the insider would likely have access to the key as well unless you mean someone taking a disk out of the datacenter which is pretty far fetched as an attack. Dunno if you have been in a serious DC before but the last one I was in had a retina scanner to enter and was under constant surveillance.

I 100% agree there are security policies specified by regulations that make very little sense and this might satisfy them.

Former AWS employee, this is very much not true. It doesn’t protect against every possible insider threat but does protect against a very large class of them. It is extremely not the case that you can assume an attacker who has access to the disk also has access to the key material, those are two very different things.

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