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Get a base implementation of the spec

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mratsim 2018-12-03 16:09:28 +01:00
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# beacon_chain
# Copyright (c) 2018 Status Research & Development GmbH
# Licensed and distributed under either of
# * MIT license (license terms in the root directory or at http://opensource.org/licenses/MIT).
# * Apache v2 license (license terms in the root directory or at http://www.apache.org/licenses/LICENSE-2.0).
# at your option. This file may not be copied, modified, or distributed except according to those terms.
# This file implements a test vectors generator for the shuffling algorithm described in the Ethereum
# specs as of https://github.com/ethereum/eth2.0-specs/blob/2983e68f0305551083fac7fcf9330c1fc9da3411/specs/core/0_beacon-chain.md#get_new_shuffling
# Reference picture: http://vitalik.ca/files/ShuffleAndAssign.png
# and description from Py-EVM: https://github.com/ethereum/py-evm/blob/f2d0d5d187400ba46a6b8f5b1f1c9997dc7fbb5a/eth/beacon/helpers.py#L272-L344
#
# validators:
# [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]
# After shuffling:
# [6, 0, 2, 12, 14, 8, 10, 4, 9, 1, 5, 13, 15, 7, 3, 11]
# Split by slot:
# [
# [6, 0, 2, 12, 14], [8, 10, 4, 9, 1], [5, 13, 15, 7, 3, 11]
# ]
# Split by shard:
# [
# [6, 0], [2, 12, 14], [8, 10], [4, 9, 1], [5, 13, 15] ,[7, 3, 11]
# ]
# Fill to output:
# [
# # slot 0
# [
# ShardAndCommittee(shard_id=0, committee=[6, 0]),
# ShardAndCommittee(shard_id=1, committee=[2, 12, 14]),
# ],
# # slot 1
# [
# ShardAndCommittee(shard_id=2, committee=[8, 10]),
# ShardAndCommittee(shard_id=3, committee=[4, 9, 1]),
# ],
# # slot 2
# [
# ShardAndCommittee(shard_id=4, committee=[5, 13, 15]),
# ShardAndCommittee(shard_id=5, committee=[7, 3, 11]),
# ],
# ]
# Note that as of 2018-12-03, several implementations are outdated
# as they are still using dynasty or min_committee_size that are not in the specs
# ################################################################
#
# Imports and simplified types
#
# ################################################################
from typing import(
List, Any, Dict, NewType
)
from enum import IntEnum
Hash32 = NewType('Hash32', bytes)
class ValidatorStatus(IntEnum):
PENDING_ACTIVATION = 0
ACTIVE = 1
EXITED_WITHOUT_PENALTY = 2
EXITED_WITH_PENALTY = 3
# Not in specs anymore - https://github.com/ethereum/eth2.0-specs/issues/216
PENDING_EXIT = 255
class ValidatorRecord:
fields = {
# Status code
'status': 'ValidatorStatus'
}
def __init__(self, **kwargs):
for k in self.fields.keys():
assert k in kwargs or k in self.defaults
setattr(self, k, kwargs.get(k, self.defaults.get(k)))
def __setattr__(self, name: str, value: Any) -> None:
super().__setattr__(name, value)
def __getattribute__(self, name: str) -> Any:
return super().__getattribute__(name)
class ShardAndCommittee:
fields = {
# Shard number
'shard': 'uint64',
# Validator indices
'committee': ['uint24'],
# Total validator count (for proofs of custody)
'total_validator_count': 'uint64',
}
def __init__(self, **kwargs):
for k in self.fields.keys():
assert k in kwargs or k in self.defaults
setattr(self, k, kwargs.get(k, self.defaults.get(k)))
def __setattr__(self, name: str, value: Any) -> None:
super().__setattr__(name, value)
def __getattribute__(self, name: str) -> Any:
return super().__getattribute__(name)
# ################################################################
#
# Environment variables
#
# ################################################################
SHARD_COUNT = 2**10 # 1024
EPOCH_LENGTH = 2**6 # 64 slots, 6.4 minutes
TARGET_COMMITTEE_SIZE = 2**8 # 256 validators
# ################################################################
#
# Procedures (copy-pasted from specs)
#
# ################################################################
def get_active_validator_indices(validators: [ValidatorRecord]) -> List[int]:
"""
Gets indices of active validators from ``validators``.
"""
return [i for i, v in enumerate(validators) if v.status in [ACTIVE, PENDING_EXIT]]
def shuffle(values: List[Any], seed: Hash32) -> List[Any]:
"""
Returns the shuffled ``values`` with ``seed`` as entropy.
"""
values_count = len(values)
# Entropy is consumed from the seed in 3-byte (24 bit) chunks.
rand_bytes = 3
# The highest possible result of the RNG.
rand_max = 2 ** (rand_bytes * 8) - 1
# The range of the RNG places an upper-bound on the size of the list that
# may be shuffled. It is a logic error to supply an oversized list.
assert values_count < rand_max
output = [x for x in values]
source = seed
index = 0
while index < values_count - 1:
# Re-hash the `source` to obtain a new pattern of bytes.
source = hash(source)
# Iterate through the `source` bytes in 3-byte chunks.
for position in range(0, 32 - (32 % rand_bytes), rand_bytes):
# Determine the number of indices remaining in `values` and exit
# once the last index is reached.
remaining = values_count - index
if remaining == 1:
break
# Read 3-bytes of `source` as a 24-bit big-endian integer.
sample_from_source = int.from_bytes(source[position:position + rand_bytes], 'big')
# Sample values greater than or equal to `sample_max` will cause
# modulo bias when mapped into the `remaining` range.
sample_max = rand_max - rand_max % remaining
# Perform a swap if the consumed entropy will not cause modulo bias.
if sample_from_source < sample_max:
# Select a replacement index for the current index.
replacement_position = (sample_from_source % remaining) + index
# Swap the current index with the replacement index.
output[index], output[replacement_position] = output[replacement_position], output[index]
index += 1
else:
# The sample causes modulo bias. A new sample should be read.
pass
return output
def split(values: List[Any], split_count: int) -> List[Any]:
"""
Splits ``values`` into ``split_count`` pieces.
"""
list_length = len(values)
return [
values[(list_length * i // split_count): (list_length * (i + 1) // split_count)]
for i in range(split_count)
]
def clamp(minval: int, maxval: int, x: int) -> int:
"""
Clamps ``x`` between ``minval`` and ``maxval``.
"""
if x <= minval:
return minval
elif x >= maxval:
return maxval
else:
return x
def get_new_shuffling(seed: Hash32,
validators: List[ValidatorRecord],
crosslinking_start_shard: int) -> List[List[ShardAndCommittee]]:
"""
Shuffles ``validators`` into shard committees using ``seed`` as entropy.
"""
active_validator_indices = get_active_validator_indices(validators)
committees_per_slot = clamp(
1,
SHARD_COUNT // EPOCH_LENGTH,
len(active_validator_indices) // EPOCH_LENGTH // TARGET_COMMITTEE_SIZE,
)
# Shuffle with seed
shuffled_active_validator_indices = shuffle(active_validator_indices, seed)
# Split the shuffled list into epoch_length pieces
validators_per_slot = split(shuffled_active_validator_indices, EPOCH_LENGTH)
output = []
for slot, slot_indices in enumerate(validators_per_slot):
# Split the shuffled list into committees_per_slot pieces
shard_indices = split(slot_indices, committees_per_slot)
shard_id_start = crosslinking_start_shard + slot * committees_per_slot
shards_and_committees_for_slot = [
ShardAndCommittee(
shard=(shard_id_start + shard_position) % SHARD_COUNT,
committee=indices,
total_validator_count=len(active_validator_indices),
)
for shard_position, indices in enumerate(shard_indices)
]
output.append(shards_and_committees_for_slot)
return output