Update ed25519 backend

[robert-zaremba]

Summary

Tendermint v0.35 (scheduled post Stargate) changed ed25519 backend to according to zip215
Details: tendermint/tendermint#5632

Problem Definition

For compatibility with other libraries we need to have more strict signature verification than the default one provided by stdlib.

Proposal

Simple task: use github.com/hdevalence/ed25519consensus (instead of stdlib) for ed25519 signature verification.

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[robert-zaremba]

@marbar3778 - is Tendermint v0.35 scheduled for SDK 0.40.1 or 0.41.0?

[tac0turtle]

Does the sdk have a timetable for 0.41. It's hard to say when 0.35 will be ready

[robert-zaremba]

We have a task list https://github.com/cosmos/cosmos-sdk/milestone/26 :D
But I think we can do it earlier. It should be compatible, right?

[tac0turtle]

Yea it should be compatible. I dont think the sdk does any key verification for tm ed25519 keys? If this is the case, it is safe to make this update now.

[robert-zaremba]

I'm not aware about any such place. @aaronc - do you know if we do that ?

[robert-zaremba]

There is also a security discussion about ed25519 in #4789