Transformations and Crypto

So, I'm putting this here for lack of a better place to put it...

When discussing IPLD, @jbenet brought up the concept of graph transformation programs. Basically, an IPLD object could point to to a portable/secure (e.g. compiled to webasm) program that could take the IPLD object as an input and could lazily generate some a different object as output. This would allow arbitrarily flexible abstractions (literally, turing complete). This is really useful.

However, @jbenet then noted that this could be used to add support for encrypting objects. That is, a decryption program could be written as a graph transformation that takes a key in addition to the object. After thinking about this, I realized that this isn't actually possible to do securely. In general, it's impossible to securely run untrusted code (even in a sandbox) on private data (cipertext/key). There will always be side channels by which that untrusted code can communicate with the outside world (at the end of the day, the user is a viable side channel).

I'm leaving this here as a not to future persons so nobody tries this. Basically, crypto, even decryption, must always be done by a small, carefully verified library.