The goal of the Tahoe-LAFS 100 Year Cryptography project is to \"enhance Tahoe-L

Question

The goal of the Tahoe-LAFS 100 Year Cryptography project is to "enhance Tahoe-LAFS's cryptographic system so that Tahoe shipped today/next year might remain safe from cryptographic attacks for a 100 years." Its developers are openly collaborating knowledgeable experts in the field, with at least all the information on the internet today at their disposal.

How long would such a project have secured its data had it been started 100 years ago?

Is the length of the secure period monotonically increasing as we ask the question with starting points less distant in the past?

Explanation / Answer

In 1911, there was no computer either. With much more modest goals of security for the next few months, the German army came up with the Enigma, which was broken. Before the 1970s, cryptography was essentially a military-only domain, so there were no "openly collaborating knowledgeable experts". The situation was qualitatively different. So it is a bit unfair, and of limited scientific value, to try to compare cryptographic systems before and after the seventies.

Moore's law was published by Gordon Moore in 1965, and thus was quite well known 10 years later. In 1976, people trying to build a system which would still be safe 100 years later would have accounted for Moore's law, meaning an extra 100 bits for symmetric keys, and 200 bits for hash functions (there are several variants of Moore's law, but one of the most optimistic says that every two years you can put twice as many transistors on a given die and clock them twice faster, leading to a doubling of CPU power every year). Symmetric encryption was beginning to be understood; DES had just been approved as a US standard, so, presumably, people aiming for 100-year security would have proposed something like 5-DES. They might have missed the point about block size: DES has 64-bit blocks, making it unsuitable for securely encrypting more than a few dozen gigabytes with a given key. Even if believing Moore's law, the sheer volume of today's data was not envisioned at that time.

In 1976, there was no hash function worth speaking of. The Merkle-Damg

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