Contract continuity & authentication with ST & PTs

[ch1bo]

What & Why

Previous work on the Plutus scripts ensured the Hydra Head is opened & closed on-chain honoring the off-chain agreed UTXO state. However, this was not covering two cases and goal of this feature is to

• ensure that the Hydra protocol transactions are submitted in order, and
• ensure that all participants had a chance to commit UTXOs to a Head

For that matter we will need to mint & use so-called state-thread tokens (ST) and participation tokens (PT) as described in the Hydra and eUTXO paper.

This will improve the Hydra Head security.

Functional requirements

• The Head can only be opened if all participants committed
• An open head state cannot be created "out of thin air" (skipping initial & commit stages)
• Only Head participants can do Head life-cycle transitions, e.g. abort a head.

Technical requirements

• The Hydra Head is uniquely identified by the policy id of the ST
• The ST is forwarded along the Head validator life cycle
• Each participant "receives" a PT via the v_initial script
• All PTs are required to collectCom or abort a Head All Head transactions need to be signed by one of the keys enumerated by spent PTs (token names == pkh)

Tasks

• Actually check the CollectCom transition consumes consistent PTs/STs #241
• Drop Party from ν_commit datum #242
• Check all Hydra txs signed by a Head participant #284
• Pass list of PKH to on-chain state and verify PTs minting using that #243
• MakeheadValidatorHash a parameter to the v_commit validator #259 (TBD)