Penumbra’s staking token, denoted
PEN, represents units of unbonded stake.
Penumbra treats stake bonded with a particular validator as a distinct asset,
PENb, with an epoch-varying exchange rate between
that prices in what would be a staking reward in other systems. This ensures
that all delegations to a particular validator are fungible, and can be
represented by a single token, in effect a first-class staking derivative
that represents fractional ownership of that validator’s delegation pool.
Stake bonded with different validators is not fungible, as different
validators may have different commission rates and different risk of
PENb is a shorthand for a class of assets (one per
validator), rather than a single asset.
PENb bonded to a specific
validator can be denoted
PENb(v) when it is necessary to be precise.
Each flavor of
PENb is its own first-class token, and like any other token
can be transferred between addresses, traded, sent over IBC, etc. Penumbra
itself does not attempt to pool risk across validators, but nothing prevents
third parties from building stake pools composed of these assets.
The base reward rate for bonded stake is a parameter indexed by epoch. This parameter can be thought of as a “Layer 1 Base Operating Rate”, or “L1BOR”, in that it serves as a reference rate for the entire chain. Its value is set on a per-epoch basis by a formula involving the ratio of bonded and unbonded stake, increasing when there is relatively less bonded stake and decreasing when there is relatively more. This formula should be decided and adjusted by governance.
Each validator declares a commission percentage , also indexed by epoch, which is subtracted from the base reward rate to get a validator-specific reward rate
The base exchange rate between
PENb is given by the function
which measures the cumulative
depreciation of unbonded
PEN relative to bonded
PENb from genesis up to
epoch . However, because
PENb is not a single asset but a family of
per-validator assets, this is only a base rate.
The actual exchange rate between
PENb(v) bonded to validator
accounts for commissions by substituting the validator-specific rate
in place of the base rate to get
PEN to validator at epoch results in
PENb(v) from validator at
epoch results in
PEN. Thus, delegating at epoch
and undelegating at epoch results in a return of i.e., the staking
reward compounded only over the period during which the stake was bonded.
Discounting newly bonded stake by the cumulative depreciation of unbonded stake since genesis means that all bonded stake can be treated as if it had been bonded since genesis, which allows newly unbonded stake to always be inflated by the cumulative appreciation since genesis. This mechanism avoids the need to track the age of any particular delegation to compute its rewards, and makes all shares of each validator’s delegation pool fungible.