Source code for lib.hashing
# -*- coding: utf-8 -*-
# Copyright Martin Manns
# Distributed under the terms of the GNU General Public License
# --------------------------------------------------------------------
# pyspread is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# pyspread is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with pyspread. If not, see <http://www.gnu.org/licenses/>.
# --------------------------------------------------------------------
"""
File hashing services
**Provides**
* :func:`genkey` - Generates hash key
* :func:`sign` - Returns a signature for a given file
* :func:`verify` - Verifies file against signature
"""
import ast
from hashlib import blake2b
from hmac import compare_digest
import secrets
[docs]
def genkey(nbytes: int = 64) -> bytes:
"""Returns a random byte sting that may be used as signature key
:param nbytes: Length of key
:return: Random byte string of length nbytes
"""
return secrets.token_bytes(nbytes)
[docs]
def sign(data: bytes, key: bytes) -> bytes:
"""Returns signature for file using blake2b
Note: 64 bytes is the maximum that is supported in Python's BLAKE2b
:param data: Data to be signed
:param key: Signature key, len(key) <= 64
:return: File signature hexdigest, encoded in utf-8
"""
if not key:
raise ValueError("No signature key defined")
if not isinstance(key, bytes):
key = ast.literal_eval(key)
if len(key) > blake2b.MAX_KEY_SIZE:
key = key[:blake2b.MAX_KEY_SIZE]
raise UserWarning("Key is too long and has been truncated")
signature = blake2b(digest_size=64, key=key)
signature.update(data)
return signature.hexdigest().encode('utf-8')
[docs]
def verify(data: bytes, signature: bytes, key: bytes) -> bool:
"""Verifies a signature
:param data: Data to be verified
:param signature: Signature for verification
:param key: Signature key, len(key) <= 64
:return: True if verification was successful else False
"""
data_signature = sign(data, key)
return compare_digest(data_signature, signature)
pyspread