66 lines
2.1 KiB
Markdown
66 lines
2.1 KiB
Markdown
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# Ethereum 2.0 Altair BLS extensions
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## Table of contents
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<!-- TOC -->
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<!-- START doctoc generated TOC please keep comment here to allow auto update -->
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<!-- DON'T EDIT THIS SECTION, INSTEAD RE-RUN doctoc TO UPDATE -->
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- [Introduction](#introduction)
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- [Constants](#constants)
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- [Extensions](#extensions)
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- [`eth2_aggregate_pubkeys`](#eth2_aggregate_pubkeys)
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- [`eth2_fast_aggregate_verify`](#eth2_fast_aggregate_verify)
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<!-- END doctoc generated TOC please keep comment here to allow auto update -->
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<!-- /TOC -->
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## Introduction
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A number of extensions are defined to handle BLS signatures in the Altair upgrade.
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Knowledge of the [phase 0 specification](../phase0/beacon-chain.md) is assumed, including type definitions.
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## Constants
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| Name | Value |
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| - | - |
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| `G2_POINT_AT_INFINITY` | `BLSSignature(b'\xc0' + b'\x00' * 95)` |
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## Extensions
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### `eth2_aggregate_pubkeys`
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An additional function `AggregatePKs` is defined to extend the
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[IETF BLS signature draft standard v4](https://tools.ietf.org/html/draft-irtf-cfrg-bls-signature-04)
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spec referenced in the phase 0 document.
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```python
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def eth2_aggregate_pubkeys(pubkeys: Sequence[BLSPubkey]) -> BLSPubkey:
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"""
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Return the aggregate public key for the public keys in ``pubkeys``.
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NOTE: the ``+`` operation should be interpreted as elliptic curve point addition, which takes as input
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elliptic curve points that must be decoded from the input ``BLSPubkey``s.
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This implementation is for demonstrative purposes only and ignores encoding/decoding concerns.
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Refer to the BLS signature draft standard for more information.
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"""
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assert len(pubkeys) > 0
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result = copy(pubkeys[0])
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for pubkey in pubkeys[1:]:
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result += pubkey
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return result
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```
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### `eth2_fast_aggregate_verify`
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```python
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def eth2_fast_aggregate_verify(pubkeys: Sequence[BLSPubkey], message: Bytes32, signature: BLSSignature) -> bool:
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"""
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Wrapper to ``bls.FastAggregateVerify`` accepting the ``G2_POINT_AT_INFINITY`` signature when ``pubkeys`` is empty.
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"""
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if len(pubkeys) == 0 and signature == G2_POINT_AT_INFINITY:
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return True
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return bls.FastAggregateVerify(pubkeys, message, signature)
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```
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