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discuss using the block header to randomize the distribution index

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Jude Nelson
2019-01-06 00:44:15 -05:00
parent 220a4676ad
commit 027ff1571e
1 changed files with 21 additions and 3 deletions
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24
sip/sip-001-burn-election.md
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@@ -380,6 +380,8 @@ all chain tips). The next block is determined with the following algorithm:
```python
# inputs:
# * BLOCK_HEADER -- the burn chain block header, which contains the PoW nonce
#
# * BURNS -- a mapping from public keys to burn amounts and block hashes,
# generated from the valid set of commit & burn transaction pairs.
#
@@ -394,10 +396,13 @@ all chain tips). The next block is determined with the following algorithm:
# * BLOCK_HASH -- the winning block hash
# * NEW_SEED -- the new public seed
def make_distribution(BURNS):
def make_distribution(BURNS, BLOCK_HEADER):
DISTRIBUTION = []
BURN_OFFSET = 0
for (PUBKEY, (BURN_AMOUNT, BLOCK_HASH)) in sorted(BURNS.items()):
BURN_ORDER = dict([(hash(PUBKEY + BLOCK_HEADER.nonce),
(PUBKEY, BURN_AMOUNT, BLOCK_HASH))
for (PUBKEY, (BURN_AMOUNT, BLOCK_HASH)) in BURNS.items()])
for (_, (PUBKEY, BURN_AMOUNT, BLOCK_HASH)) in sorted(BURN_ORDER.items()):
DISTRIBUTION.append((BURN_OFFSET, PUBKEY, BLOCK_HASH))
BURN_OFFSET += BURN_AMOUNT
return DISTRIBUTION
@@ -421,7 +426,12 @@ Only one leader will win an election. It is not guaranteed that the block the
leader produces is valid or builds off of the best Stacks fork. However,
once a leader is elected, all peers will know enough information about the
leader's decisions that the block data can be submitted and relayed by any other
peer in the network.
peer in the network. Crucially, the winner of the sortition will be apparent to
any peer without each candidate needing to submit their blocks beforehand.
The distribution is sampled using the _previous VRF seed_ and the _current block
PoW solution_. This ensures that no one -- not even the PoW miner -- knows
which public key in the burn distribution will be selected with the PoW seed.
Leaders can make their burn chain transactions and
construct their blocks however they want. So long as the burn chain transactions
@@ -471,6 +481,14 @@ without a valid block being produced, because (1) attempting to produce a block
is costly and (2) users can easily form burning pools to advance the
state of the Stacks chain even if the "usual" leaders go offline.
As an added security measure, the distribution into which the previous epoch's
VRF seed will index will be randomly structured using the VRF seed and the PoW
nonce. This dissuades PoW miners from omitting or including burn transactions
in order to influence where the VRF seed will index into the weight
distribution. Since the PoW miner is not expected to be able
to generate more than one PoW nonce per epoch, the burn chain miners won't know
in advance which leader will be elected.
# Operation as a leader
The Stacks blockchain uses a hybrid approach for generating block data: it can