ethereum.forks.prague.vm.precompiled_contracts.point_evaluation

Ethereum Virtual Machine (EVM) POINT EVALUATION PRECOMPILED CONTRACT.

.. contents:: Table of Contents :backlinks: none :local:

Introduction

Implementation of the POINT EVALUATION precompiled contract.

FIELD_ELEMENTS_PER_BLOB

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FIELD_ELEMENTS_PER_BLOB = 4096

BLS_MODULUS

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BLS_MODULUS = 52435875175126190479447740508185965837690552500527637822603658699938581184513

VERSIONED_HASH_VERSION_KZG

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VERSIONED_HASH_VERSION_KZG = b"\x01"

point_evaluation

A pre-compile that verifies a KZG proof which claims that a blob (represented by a commitment) evaluates to a given value at a given point.

Parameters

evm : The current EVM frame.

def point_evaluation(​evm: Evm​) -> None:
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    """
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    A pre-compile that verifies a KZG proof which claims that a blob
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    (represented by a commitment) evaluates to a given value at a given point.
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    Parameters
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    ----------
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    evm :
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        The current EVM frame.
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    """
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    data = evm.message.data
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    if len(data) != 192:
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        raise KZGProofError
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    versioned_hash = data[:32]
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    z = Bytes32(data[32:64])
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    y = Bytes32(data[64:96])
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    commitment = KZGCommitment(data[96:144])
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    proof = Bytes48(data[144:192])
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    # GAS
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    charge_gas(evm, GAS_POINT_EVALUATION)
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    if kzg_commitment_to_versioned_hash(commitment) != versioned_hash:
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        raise KZGProofError
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    # Verify KZG proof with z and y in big endian format
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    try:
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        kzg_proof_verification = verify_kzg_proof(commitment, z, y, proof)
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    except Exception as e:
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        raise KZGProofError from e
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    if not kzg_proof_verification:
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        raise KZGProofError
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    # Return FIELD_ELEMENTS_PER_BLOB and BLS_MODULUS as padded
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    # 32 byte big endian values
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    evm.output = Bytes(
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        U256(FIELD_ELEMENTS_PER_BLOB).to_be_bytes32()
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        + U256(BLS_MODULUS).to_be_bytes32()
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    )