Source code for spiral.keys

import fcntl
import os
import struct

from nacl.public import PrivateKey
from zope.interface import implementer, Attribute, Interface


counterStruct = struct.Struct('<Q')


class IKeyAndNonceScheme(Interface):
    """
    A key and nonce generation scheme.
    """

    key = Attribute('A nacl.public.PrivateKey instance.')

    def nonce(longterm=False):
        """
        Generate a nonce.

        :param longterm: True to increment the long-term counter; False to
            increment the short-term counter.
        :returns: 16 bytes.
        """


@implementer(IKeyAndNonceScheme)
class Keydir(object):
    """
    A key loaded from disk, probably generated by ``curvecpmakekey``.

    Nonces are eight random bytes concatenated to a counter persisted to disk.

    :param keydir: The path to a key directory.
    """

    def __init__(self, keydir):
        self.keydir = keydir
        with open(self.expertsFile('secretkey')) as infile:
            self.key = PrivateKey(infile.read())

    def expertsFile(self, name):
        return os.path.join(self.keydir, '.expertsonly', name)

    def nonce(self, longterm=False):
        with open(self.expertsFile('lock'), 'r+') as lockfile:
            fcntl.lockf(lockfile, fcntl.LOCK_EX)
            with open(self.expertsFile('noncecounter'), 'rb+') as noncefile:
                data = noncefile.read()
                counter, = counterStruct.unpack(data)
                counter += 1048576 if longterm else 1
                noncefile.seek(0)
                data = counterStruct.pack(counter)
                noncefile.write(data)
        return os.urandom(8) + data


@implementer(IKeyAndNonceScheme)
class EphemeralKey(object):
    """
    An unpersisted, randomly-generated key.

    Nonces are 16 random bytes.
    """

    def __init__(self):
        self.key = PrivateKey.generate()

    def nonce(self, longterm=False):
        return os.urandom(16)