Merge mintkey in

[jaekwon]

We need to use bcrypt for cryptostore.
Lets merge in https://github.com/tendermint/mintkey/blob/master/cmd/mintkey/common.go

[ethanfrey]

This is noted in a comment. I wasn't sure how to set up bcrypt securely, so I left it as a TODO until someone did it wrtie. (Better missing than buggy). Could you make a PR to show me how?

The code to modify is here:
https://github.com/tendermint/go-crypto/blob/master/keys/cryptostore/encoder.go#L23-L26

I guess it should do something like:
https://github.com/tendermint/mintkey/blob/master/cmd/mintkey/common.go#L68-L77

But not sure how to deal with salts and headers. Also, we need to clean up the local file format as per #13 so maybe we should do that to add support for salts.

I don't know the proper design here. Very happy to have someone with more experience in cryptography work on this.

[ethanfrey]

Is bcrypt even the right choice?

Scrypt seems much better against GPU cracking, and is in the go/x/crypto libs:
https://godoc.org/golang.org/x/crypto/scrypt

Or even other algorithms like argon2, the winner of the password hashing competition:
https://news.ycombinator.com/item?id=10863131

Notes on go implementations, which seem not really production-ready:
https://github.com/magical/argon2
golang/go#19896

[adrianbrink]

This is implemented in #38

[adrianbrink]

I think we should stick with the proven crypto, which in this case is bcrypt. It has aged nicely for 14 years without any theoretical vulnerabilities. Scrypt with 3-4 is much less proven. It is more memory heavy and hence better against FPGA cracking.

Some sources:
https://security.stackexchange.com/questions/26245/is-bcrypt-better-than-scrypt#26253

[ethanfrey]

It would be great to make this configurable somehow. At least bcrypt and scrypt. But I think that is related to #13

[adrianbrink]

I'll look into that once I have some time

[zramsay]

#38

[ebuchman]

configurable kdf is done in #58 via the armor headers. we can add support for scrypt if we like down the road.