Source code for file_encryptor.key_generators

#!/usr/bin/env python
# -*- coding: utf-8 -*-

# The MIT License (MIT)
#
# Copyright (c) 2014 Storj Labs
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# of this software and associated documentation files (the "Software"), to deal
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# furnished to do so, subject to the following conditions:
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# The above copyright notice and this permission notice shall be included in
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# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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import hashlib
import hmac

from file_encryptor.settings import CHUNK_SIZE, DEFAULT_HMAC_PASSPHRASE


def sha256_file(path):
    """Calculate sha256 hex digest of a file.

    :param path: The path of the file you are calculating the digest of.
    :type path: str
    :returns: The sha256 hex digest of the specified file.
    :rtype: builtin_function_or_method
    """
    h = hashlib.sha256()

    with open(path, 'rb') as f:
        for chunk in iter(lambda: f.read(CHUNK_SIZE), b''):
            h.update(chunk)

    return h.hexdigest()


def key_from_file(filename, passphrase):
    """Calculate convergent encryption key.

    This takes a filename and an optional passphrase.
    If no passphrase is given, a default is used.
    Using the default passphrase means you will be
    vulnerable to confirmation attacks and
    learn-partial-information attacks.

    :param filename: The filename you want to create a key for.
    :type filename: str
    :param passphrase: The passphrase you want to use to encrypt the file.
    :type passphrase: str or None
    :returns: A convergent encryption key.
    :rtype: str
    """
    hexdigest = sha256_file(filename)

    if passphrase is None:
        passphrase = DEFAULT_HMAC_PASSPHRASE

    return keyed_hash(hexdigest, passphrase)


def keyed_hash(digest, passphrase):
    """Calculate a HMAC/keyed hash.

    :param digest: Digest used to create hash.
    :type digest: str
    :param passphrase: Passphrase used to generate the hash.
    :type passphrase: str
    :returns: HMAC/keyed hash.
    :rtype: str
    """
    encodedPassphrase = passphrase.encode()
    encodedDigest = digest.encode()

    return hmac.new(encodedPassphrase, encodedDigest, hashlib.sha256).digest()