lib/utils/hash.py

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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