[lkowalcz]

Anyone want to speculate about how the data is being "encrypted"? It seems like they don't want to say, which immediately sets off red flags in my head...

I am pretty sure homomorphic encryption is not being used. I think if they are doing anything rigorous, maybe they are using order-preserving encryption (http://www.cc.gatech.edu/~aboldyre/papers/bclo.pdf). This would mean that the only valid operations on the ciphertexts are comparison operations. I can't seem to find anywhere where numer.ai actually says how to interact with the "encrypted" data. I think it's a little strange that they would suggest that they are using homomorphic encryption yet have only comparison operations actually make sense on their "encrypted" data.

A second hypothesis would be that no encryption is being used at all, and this is just unlabeled features that have been renormalized within [0,1].

A third would be that order-preserving encryption is being used, but in an ineffective way which is basically just resulting in the second scenario. (understanding the security guarantees of order-preserving encryption is practice is very complicated)