PoS - verify validator keys ownership with signatures

[tzemanovic]

For the on-chain validator account creation and for transactions to change consensus key (pending on #36), we must also require that a signature with the consensus key is attached to the transactions to verify the key's ownership. Depends on #85 to be able to attach multiple signatures to a tx.

For this, we should update the client commands and the PoS VP to enforce this rule.

[tzemanovic]

another way would be to have some "challenge" in the ledger's state that init-validator txs would have to sign over to verify ownership of the relevant PKs that they're trying to use for their validator account - sketched out here https://excalidraw.com/#json=GzskiES12LxvLl-7Y_wGk,qPn9jmoqX2VUnMbJSm86hQ

Other PKs we might want to verify are the protocol key and eth bridge cold and hot key.

For genesis validators, we might need to do something else as those are created before there's any ledger or chain ID. We can e.g. have some pseudo random hash that we ask validators to sign over with those keys.

[cwgoes]

@brentstone can you take this on as part of the PoS work?

[tzemanovic]

The genesis part will be solved by #685, now #1840, but we'll still need something for init-validator tx. I think we could use multisig signatures for this (#81/#85)

[tzemanovic]

in #1840 we're authorizing pre-genesis init-validator tx with all these validator keys:

namada/genesis/localnet/src/pre-genesis/validator-0/transactions.toml

Lines 9 to 31 in 3968fef

	[validator_account.account_key]
	pk = "pktest1qpqznlesv6fcgsz9x4rsn7l4dsnp7h5sswvs9atw0zgq3uwp0jll2r42szz"
	authorization = "sigtest1qrcy6a095uj6n8ryc9fkfw3hn2jn285g82hdratzrvmg22xp5qdmyr7e9q97t77v4zr8a73x4c3k53pcec3mp4ugt5jqd2w0fvd7nhcp0ajsk4"
	[validator_account.consensus_key]
	pk = "pktest1qpk2a5m26cgnrp32l2c2hss03draxwnctu92llhlr6kjesn2kt892k2kklp"
	authorization = "sigtest1qzajuey408zf66wgw8x3awd5jx9x249csx63n80clehj238qqpsf9cdr630edqjr8fw95vywlngy368r087sge2xy89qpcsrxvwtm3gr0h6g79"
	[validator_account.protocol_key]
	pk = "pktest1qpfv9pj4zmelcg98rtw8wezztzdgpuczuxjmx946klkxajmvvcxjz3vsv63"
	authorization = "sigtest1qz0aerskgtzwmgxwgml72zyz4974njfz6s9dl7r399d0v64pzsmctkwe8f28dwyef52hklj6r2fqmeypncvv3qg2x4hg4u3g23kw23qt73uzmy"
	[validator_account.tendermint_node_key]
	pk = "pktest1qp7shxxfdkp8ft8xfkgf2vqy7u6effdp82w0cq6aq8575txul33t63dyd68"
	authorization = "sigtest1qq87l6zjuswmrfeysxp8j0tu5zlklnswzaqgcuyaq23p49hhvupa57r3rwrh3txfuvq8lh5e7wu7d90js8cn7a7dygs7v5yx2a9ljtqxwl0chr"
	[validator_account.eth_hot_key]
	pk = "pktest1qypdzza7uqtklzzs50hhy07h5ru9p0v8y5666wwulqnd3mdpuj0tcxsgck694"
	authorization = "sigtest1q9qtzvwlqhnft5jgeyms2w757dlly8rjg4g89593ayhan0fx7uvjzvm7r7ltgsly9tp6783pqpl6ezxty240udrrknxmunymz6lm523qqqwx72ra"
	[validator_account.eth_cold_key]
	pk = "pktest1qypzca0n6l890jc83nk5lljuzps04xmfccz3f87xc6ez40t2wvql48s52cx8r"
	authorization = "sigtest1q8qmjstc2jtt3dwueepv0njk9te5qpj6z9yj6w0duhagswz80vyws3ywdsy9n49qnjecvnpxwlna3578vn423tgd4rrtss06ejgkj7c5qyv22nm6"

We should use multisig to do the same for the regular init-validator tx

[tzemanovic]

we still need on-chain init-validator sigs check