[Cryptography] Came up with a weird use case, got questions

Bill Frantz frantz at pwpconsult.com
Mon Jan 7 13:38:08 EST 2019


On 1/7/19 at 10:38 PM, phill at hallambaker.com (Phillip 
Hallam-Baker) wrote:

>The most robust schemes in practice are going to involve ceremony and some
>form of trusted hardware. We could build a HSM such that it will only
>release the data if it receives a signed statement of the current time from
>a trusted source. Throw it in a vault and bring it out after 100 years. It
>will probably work. If built right.
>
>Establishing a quorate notary that can be trusted to sign time is rather
>easier. Each notary would have to delegate its function to a successor
>periodically but that should not be too difficult to ensure.
>
>Of course there is then a real risk that the data is lost because the
>notaries don't continue their function.

There are a lot of causes of risk of data loss. Bit rot in 
storage media is a real worry. The best solution is to copy the 
data regularly. For the encrypted data, the only downside is the 
storage cost. For the keys it introduces a new complication in 
maintaining secrecy.

There is also risk of transistor failure in the HSM due to 
dopant migration over time. We don't have experience with 
transistor equipment over long periods of time. Our experience 
with tube equipment, which is about 100 years, is that 
electrolytic capacitors die unless treated with a low voltage 
for a while to rebuilt their insulation layer. Sometimes they 
die anyway. I can't think of a way of keeping a HSM alive over 
long periods of time, certainly not one that is anywhere near as 
easy as copying data.

Cheers - Bill

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