ethereum.forks.bpo3.vm.precompiled_contracts.p256verifyethereum.forks.bpo4.vm.precompiled_contracts.p256verify

Ethereum Virtual Machine (EVM) P256VERIFY PRECOMPILED CONTRACT.

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

Introduction

Implementation of the P256VERIFY precompiled contract.

p256verify

Verifies a P-256 signature.

Parameters

evm : The current EVM frame.

def p256verify(​evm: Evm​) -> None:
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    """
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    Verifies a P-256 signature.
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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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    # GAS
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    charge_gas(evm, GAS_P256VERIFY)
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    if len(data) != 160:
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        return
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    # OPERATION
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    message_hash_bytes = buffer_read(data, U256(0), U256(32))
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    message_hash = Hash32(message_hash_bytes)
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    r = U256.from_be_bytes(buffer_read(data, U256(32), U256(32)))
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    s = U256.from_be_bytes(buffer_read(data, U256(64), U256(32)))
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    public_key_x = U256.from_be_bytes(
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        buffer_read(data, U256(96), U256(32))
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    )  # qx
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    public_key_y = U256.from_be_bytes(
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        buffer_read(data, U256(128), U256(32))
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    )  # qy
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    # Signature component bounds:
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    # Both r and s MUST satisfy 0 < r < n and 0 < s < n
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    if r <= U256(0) or r >= SECP256R1N:
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        return
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    if s <= U256(0) or s >= SECP256R1N:
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        return
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    # Public key bounds:
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    # Both qx and qy MUST satisfy 0 ≤ qx < p and 0 ≤ qy < p
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    # U256 is unsigned, so we don't need to check for < 0
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    if public_key_x >= SECP256R1P:
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        return
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    if public_key_y >= SECP256R1P:
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        return
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    # Point should not be at infinity (represented as (0, 0))
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    if public_key_x == U256(0) and public_key_y == U256(0):
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        return
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    # Point validity: The point (qx, qy) MUST satisfy the curve equation
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    # qy^2 ≡ qx^3 + a*qx + b (mod p)
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    if not is_on_curve_secp256r1(public_key_x, public_key_y):
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        return
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    try:
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        secp256r1_verify(r, s, public_key_x, public_key_y, message_hash)
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    except InvalidSignatureError:
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        return
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    evm.output = left_pad_zero_bytes(b"\x01", 32)