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"""Utilities for KNX Secure."""
from cryptography.hazmat.primitives import hashes
def bytes_xor(a: bytes, b: bytes) -> bytes: # pylint: disable=invalid-name
"""
XOR two bytes values.
Different lengths raise ValueError.
"""
if len(a) != len(b):
raise ValueError("Length of a and b must be equal.")
return (int.from_bytes(a, "big") ^ int.from_bytes(b, "big")).to_bytes(len(a), "big")
def byte_pad(data: bytes, block_size: int) -> bytes:
"""Pad data with 0x00 until its length is a multiple of block_size."""
if remainder := len(data) % block_size:
return data + bytes(block_size - remainder)
return data
def sha256_hash(data: bytes) -> bytes:
"""Calculate SHA256 hash of data."""
digest = hashes.Hash(hashes.SHA256())
digest.update(data)
return digest.finalize()
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