HSMs are tamper-resistant/tamper-responding devices with memory/processor inside the protected envelope. With an HSM, your key lives inside, and all operations happen on the security processor.
HSA is an Amazon term for a PC with an HSM inside. The data-at-rest might be protected by the HSM (full disk crypto with a dongle used to decrypt at boot), but the actual keys get decrypted into the host PC's RAM, and further customer-accessible calculations happen in the PC CPU.
Anyone who can tamper with the PC can read the keys!
There are two risks this exposes you to:
1) Someone goes into the datacenter and physically attacks the HSA.
2) Someone legally compels the owner of the HSA to subvert the HSA.
I'm not as worried about #1 (these are equinix tier-4 datacenters; someone rolling in with some M4s and a bulldozer and such is great for Hollywood. Insider threat probably still exists with the HSA even though normal operation is two-employee, though.) I'm incredibly worried about #2, since the bar for #2 is hella low for emails older than 6mo.
I believe ECPA older-than-6mo would be sufficient to compel the email KMS key as mere instrumentality, so even a the fairly low bar today of warrant wouldn't be required.
3) Exploit programmatic access or side-channel attacks on the data.
If the server can decrypt the data and this is driven by code on the box, then you're in a DRM-like situation trying to hide data from a program that has legitimate access.
As you alluded to earlier protecting data at rest doesn't protecting during use.
Comments
Can you explain the difference between HSM and HSA, or at least point to a good resource for understanding the difference? Thanks.
HSMs are tamper-resistant/tamper-responding devices with memory/processor inside the protected envelope. With an HSM, your key lives inside, and all operations happen on the security processor.
HSA is an Amazon term for a PC with an HSM inside. The data-at-rest might be protected by the HSM (full disk crypto with a dongle used to decrypt at boot), but the actual keys get decrypted into the host PC's RAM, and further customer-accessible calculations happen in the PC CPU.
Anyone who can tamper with the PC can read the keys!
There are two risks this exposes you to:
1) Someone goes into the datacenter and physically attacks the HSA.
2) Someone legally compels the owner of the HSA to subvert the HSA.
I'm not as worried about #1 (these are equinix tier-4 datacenters; someone rolling in with some M4s and a bulldozer and such is great for Hollywood. Insider threat probably still exists with the HSA even though normal operation is two-employee, though.) I'm incredibly worried about #2, since the bar for #2 is hella low for emails older than 6mo.
I believe ECPA older-than-6mo would be sufficient to compel the email KMS key as mere instrumentality, so even a the fairly low bar today of warrant wouldn't be required.
There's a third risk here.
3) Exploit programmatic access or side-channel attacks on the data.
If the server can decrypt the data and this is driven by code on the box, then you're in a DRM-like situation trying to hide data from a program that has legitimate access.
As you alluded to earlier protecting data at rest doesn't protecting during use.