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# Copyright (C) 2006, 2007, 2010, 2011 Google Inc.

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# General Public License for more details.

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"""Utility functions for hashing.

"""

import os

import hmac

from ganeti import compat

def Sha1Hmac(key, text, salt=None):

  """Calculates the HMAC-SHA1 digest of a text.

  HMAC is defined in RFC2104.

  @type key: string

  @param key: Secret key

  @type text: string

  """

  if salt:

    salted_text = salt + text

  else:

    salted_text = text

  return hmac.new(key, salted_text, compat.sha1).hexdigest()

def VerifySha1Hmac(key, text, digest, salt=None):

  """Verifies the HMAC-SHA1 digest of a text.

  HMAC is defined in RFC2104.

  @type key: string

  @param key: Secret key

  @type text: string

  @type digest: string

  @param digest: Expected digest

  @rtype: bool

  @return: Whether HMAC-SHA1 digest matches

  """

  return digest.lower() == Sha1Hmac(key, text, salt=salt).lower()

def _FingerprintFile(filename):

  """Compute the fingerprint of a file.

  If the file does not exist, a None will be returned

  instead.

  @type filename: str

  @param filename: the filename to checksum

  @rtype: str

  @return: the hex digest of the sha checksum of the contents

      of the file

  """

  if not (os.path.exists(filename) and os.path.isfile(filename)):

    return None

  f = open(filename)

  fp = compat.sha1_hash()

  while True:

    data = f.read(4096)

    if not data:

      break

    fp.update(data)

  return fp.hexdigest()

def FingerprintFiles(files):

  """Compute fingerprints for a list of files.

  @type files: list

  @param files: the list of filename to fingerprint

  @rtype: dict

  @return: a dictionary filename: fingerprint, holding only

      existing files

  """

  ret = {}

  for filename in files:

    cksum = _FingerprintFile(filename)

    if cksum:

      ret[filename] = cksum

  return ret