basic functionalty

modules/Crypto/Random/Fortuna/FortunaAccumulator.py

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+# -*- coding: ascii -*-
+#
+#  FortunaAccumulator.py : Fortuna's internal accumulator
+#
+# Written in 2008 by Dwayne C. Litzenberger <dlitz@dlitz.net>
+#
+# ===================================================================
+# The contents of this file are dedicated to the public domain.  To
+# the extent that dedication to the public domain is not available,
+# everyone is granted a worldwide, perpetual, royalty-free,
+# non-exclusive license to exercise all rights associated with the
+# contents of this file for any purpose whatsoever.
+# No rights are reserved.
+#
+# 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 AUTHORS OR COPYRIGHT HOLDERS
+# BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+# ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+# CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+# SOFTWARE.
+# ===================================================================
+
+__revision__ = "$Id$"
+
+import sys
+if sys.version_info[0] == 2 and sys.version_info[1] == 1:
+    from Crypto.Util.py21compat import *
+from Crypto.Util.py3compat import *
+    
+from binascii import b2a_hex
+import time
+import warnings
+
+from Crypto.pct_warnings import ClockRewindWarning
+import SHAd256
+
+# If the system has monotonic time, we'll use it.
+from Crypto.Util._time import maybe_monotonic_time
+
+import FortunaGenerator
+
+class FortunaPool(object):
+    """Fortuna pool type
+
+    This object acts like a hash object, with the following differences:
+
+        - It keeps a count (the .length attribute) of the number of bytes that
+          have been added to the pool
+        - It supports a .reset() method for in-place reinitialization
+        - The method to add bytes to the pool is .append(), not .update().
+    """
+
+    digest_size = SHAd256.digest_size
+
+    def __init__(self):
+        self.reset()
+
+    def append(self, data):
+        self._h.update(data)
+        self.length += len(data)
+
+    def digest(self):
+        return self._h.digest()
+
+    def hexdigest(self):
+        if sys.version_info[0] == 2:
+            return b2a_hex(self.digest())
+        else:
+            return b2a_hex(self.digest()).decode()
+
+    def reset(self):
+        self._h = SHAd256.new()
+        self.length = 0
+
+def which_pools(r):
+    """Return a list of pools indexes (in range(32)) that are to be included during reseed number r.
+
+    According to _Practical Cryptography_, chapter 10.5.2 "Pools":
+
+        "Pool P_i is included if 2**i is a divisor of r.  Thus P_0 is used
+        every reseed, P_1 every other reseed, P_2 every fourth reseed, etc."
+    """
+    # This is a separate function so that it can be unit-tested.
+    assert r >= 1
+    retval = []
+    mask = 0
+    for i in range(32):
+        # "Pool P_i is included if 2**i is a divisor of [reseed_count]"
+        if (r & mask) == 0:
+            retval.append(i)
+        else:
+            break   # optimization.  once this fails, it always fails
+        mask = (mask << 1) | 1L
+    return retval
+
+class FortunaAccumulator(object):
+
+    # An estimate of how many bytes we must append to pool 0 before it will
+    # contain 128 bits of entropy (with respect to an attack).  We reseed the
+    # generator only after pool 0 contains `min_pool_size` bytes.  Note that
+    # unlike with some other PRNGs, Fortuna's security does not rely on the
+    # accuracy of this estimate---we can accord to be optimistic here.
+    min_pool_size = 64  # size in bytes
+
+    # If an attacker can predict some (but not all) of our entropy sources, the
+    # `min_pool_size` check may not be sufficient to prevent a successful state
+    # compromise extension attack.  To resist this attack, Fortuna spreads the
+    # input across 32 pools, which are then consumed (to reseed the output
+    # generator) with exponentially decreasing frequency.
+    #
+    # In order to prevent an attacker from gaining knowledge of all 32 pools
+    # before we have a chance to fill them with enough information that the
+    # attacker cannot predict, we impose a rate limit of 10 reseeds/second (one
+    # per 100 ms).  This ensures that a hypothetical 33rd pool would only be
+    # needed after a minimum of 13 years of sustained attack.
+    reseed_interval = 0.100     # time in seconds
+
+    def __init__(self):
+        self.reseed_count = 0
+        self.generator = FortunaGenerator.AESGenerator()
+        self.last_reseed = None
+
+        # Initialize 32 FortunaPool instances.
+        # NB: This is _not_ equivalent to [FortunaPool()]*32, which would give
+        # us 32 references to the _same_ FortunaPool instance (and cause the
+        # assertion below to fail).
+        self.pools = [FortunaPool() for i in range(32)]     # 32 pools
+        assert(self.pools[0] is not self.pools[1])
+
+    def _forget_last_reseed(self):
+        # This is not part of the standard Fortuna definition, and using this
+        # function frequently can weaken Fortuna's ability to resist a state
+        # compromise extension attack, but we need this in order to properly
+        # implement Crypto.Random.atfork().  Otherwise, forked child processes
+        # might continue to use their parent's PRNG state for up to 100ms in
+        # some cases. (e.g. CVE-2013-1445)
+        self.last_reseed = None
+
+    def random_data(self, bytes):
+        current_time = maybe_monotonic_time()
+        if (self.last_reseed is not None and self.last_reseed > current_time): # Avoid float comparison to None to make Py3k happy
+            warnings.warn("Clock rewind detected. Resetting last_reseed.", ClockRewindWarning)
+            self.last_reseed = None
+        if (self.pools[0].length >= self.min_pool_size and
+            (self.last_reseed is None or
+             current_time > self.last_reseed + self.reseed_interval)):
+            self._reseed(current_time)
+        # The following should fail if we haven't seeded the pool yet.
+        return self.generator.pseudo_random_data(bytes)
+
+    def _reseed(self, current_time=None):
+        if current_time is None:
+            current_time = maybe_monotonic_time()
+        seed = []
+        self.reseed_count += 1
+        self.last_reseed = current_time
+        for i in which_pools(self.reseed_count):
+            seed.append(self.pools[i].digest())
+            self.pools[i].reset()
+
+        seed = b("").join(seed)
+        self.generator.reseed(seed)
+
+    def add_random_event(self, source_number, pool_number, data):
+        assert 1 <= len(data) <= 32
+        assert 0 <= source_number <= 255
+        assert 0 <= pool_number <= 31
+        self.pools[pool_number].append(bchr(source_number))
+        self.pools[pool_number].append(bchr(len(data)))
+        self.pools[pool_number].append(data)
+
+# vim:set ts=4 sw=4 sts=4 expandtab:

modules/Crypto/Random/Fortuna/FortunaGenerator.py

@@ -0,0 +1,132 @@
+# -*- coding: ascii -*-
+#
+#  FortunaGenerator.py : Fortuna's internal PRNG
+#
+# Written in 2008 by Dwayne C. Litzenberger <dlitz@dlitz.net>
+#
+# ===================================================================
+# The contents of this file are dedicated to the public domain.  To
+# the extent that dedication to the public domain is not available,
+# everyone is granted a worldwide, perpetual, royalty-free,
+# non-exclusive license to exercise all rights associated with the
+# contents of this file for any purpose whatsoever.
+# No rights are reserved.
+#
+# 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 AUTHORS OR COPYRIGHT HOLDERS
+# BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+# ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+# CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+# SOFTWARE.
+# ===================================================================
+
+__revision__ = "$Id$"
+
+import sys
+if sys.version_info[0] == 2 and sys.version_info[1] == 1:
+    from Crypto.Util.py21compat import *
+from Crypto.Util.py3compat import *
+
+import struct
+
+from Crypto.Util.number import ceil_shift, exact_log2, exact_div
+from Crypto.Util import Counter
+from Crypto.Cipher import AES
+
+import SHAd256
+
+class AESGenerator(object):
+    """The Fortuna "generator"
+
+    This is used internally by the Fortuna PRNG to generate arbitrary amounts
+    of pseudorandom data from a smaller amount of seed data.
+
+    The output is generated by running AES-256 in counter mode and re-keying
+    after every mebibyte (2**16 blocks) of output.
+    """
+
+    block_size = AES.block_size     # output block size in octets (128 bits)
+    key_size = 32                   # key size in octets (256 bits)
+
+    # Because of the birthday paradox, we expect to find approximately one
+    # collision for every 2**64 blocks of output from a real random source.
+    # However, this code generates pseudorandom data by running AES in
+    # counter mode, so there will be no collisions until the counter
+    # (theoretically) wraps around at 2**128 blocks.  Thus, in order to prevent
+    # Fortuna's pseudorandom output from deviating perceptibly from a true
+    # random source, Ferguson and Schneier specify a limit of 2**16 blocks
+    # without rekeying.
+    max_blocks_per_request = 2**16  # Allow no more than this number of blocks per _pseudo_random_data request
+
+    _four_kiblocks_of_zeros = b("\0") * block_size * 4096
+
+    def __init__(self):
+        self.counter = Counter.new(nbits=self.block_size*8, initial_value=0, little_endian=True)
+        self.key = None
+
+        # Set some helper constants
+        self.block_size_shift = exact_log2(self.block_size)
+        assert (1 << self.block_size_shift) == self.block_size
+
+        self.blocks_per_key = exact_div(self.key_size, self.block_size)
+        assert self.key_size == self.blocks_per_key * self.block_size
+
+        self.max_bytes_per_request = self.max_blocks_per_request * self.block_size
+
+    def reseed(self, seed):
+        if self.key is None:
+            self.key = b("\0") * self.key_size
+
+        self._set_key(SHAd256.new(self.key + seed).digest())
+        self.counter()  # increment counter
+        assert len(self.key) == self.key_size
+
+    def pseudo_random_data(self, bytes):
+        assert bytes >= 0
+
+        num_full_blocks = bytes >> 20
+        remainder = bytes & ((1<<20)-1)
+
+        retval = []
+        for i in xrange(num_full_blocks):
+            retval.append(self._pseudo_random_data(1<<20))
+        retval.append(self._pseudo_random_data(remainder))
+        
+        return b("").join(retval)  
+
+    def _set_key(self, key):
+        self.key = key
+        self._cipher = AES.new(key, AES.MODE_CTR, counter=self.counter)
+
+    def _pseudo_random_data(self, bytes):
+        if not (0 <= bytes <= self.max_bytes_per_request):
+            raise AssertionError("You cannot ask for more than 1 MiB of data per request")
+
+        num_blocks = ceil_shift(bytes, self.block_size_shift)   # num_blocks = ceil(bytes / self.block_size)
+
+        # Compute the output
+        retval = self._generate_blocks(num_blocks)[:bytes]
+
+        # Switch to a new key to avoid later compromises of this output (i.e.
+        # state compromise extension attacks)
+        self._set_key(self._generate_blocks(self.blocks_per_key))
+
+        assert len(retval) == bytes
+        assert len(self.key) == self.key_size
+
+        return retval
+
+    def _generate_blocks(self, num_blocks):
+        if self.key is None:
+            raise AssertionError("generator must be seeded before use")
+        assert 0 <= num_blocks <= self.max_blocks_per_request
+        retval = []
+        for i in xrange(num_blocks >> 12):      # xrange(num_blocks / 4096)
+            retval.append(self._cipher.encrypt(self._four_kiblocks_of_zeros))
+        remaining_bytes = (num_blocks & 4095) << self.block_size_shift  # (num_blocks % 4095) * self.block_size
+        retval.append(self._cipher.encrypt(self._four_kiblocks_of_zeros[:remaining_bytes]))
+        return b("").join(retval)
+
+# vim:set ts=4 sw=4 sts=4 expandtab:

modules/Crypto/Random/Fortuna/SHAd256.py

@@ -0,0 +1,98 @@
+# -*- coding: ascii -*-
+#
+#  Random/Fortuna/SHAd256.py : SHA_d-256 hash function implementation
+#
+# Written in 2008 by Dwayne C. Litzenberger <dlitz@dlitz.net>
+#
+# ===================================================================
+# The contents of this file are dedicated to the public domain.  To
+# the extent that dedication to the public domain is not available,
+# everyone is granted a worldwide, perpetual, royalty-free,
+# non-exclusive license to exercise all rights associated with the
+# contents of this file for any purpose whatsoever.
+# No rights are reserved.
+#
+# 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 AUTHORS OR COPYRIGHT HOLDERS
+# BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+# ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+# CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+# SOFTWARE.
+# ===================================================================
+
+"""\
+SHA_d-256 hash function implementation.
+
+This module should comply with PEP 247.
+"""
+
+__revision__ = "$Id$"
+__all__ = ['new', 'digest_size']
+
+import sys
+if sys.version_info[0] == 2 and sys.version_info[1] == 1:
+    from Crypto.Util.py21compat import *
+from Crypto.Util.py3compat import *
+
+from binascii import b2a_hex
+
+from Crypto.Hash import SHA256
+
+assert SHA256.digest_size == 32
+
+class _SHAd256(object):
+    """SHA-256, doubled.
+
+    Returns SHA-256(SHA-256(data)).
+    """
+
+    digest_size = SHA256.digest_size
+
+    _internal = object()
+
+    def __init__(self, internal_api_check, sha256_hash_obj):
+        if internal_api_check is not self._internal:
+            raise AssertionError("Do not instantiate this class directly.  Use %s.new()" % (__name__,))
+        self._h = sha256_hash_obj
+
+    # PEP 247 "copy" method
+    def copy(self):
+        """Return a copy of this hashing object"""
+        return _SHAd256(SHAd256._internal, self._h.copy())
+
+    # PEP 247 "digest" method
+    def digest(self):
+        """Return the hash value of this object as a binary string"""
+        retval = SHA256.new(self._h.digest()).digest()
+        assert len(retval) == 32
+        return retval
+
+    # PEP 247 "hexdigest" method
+    def hexdigest(self):
+        """Return the hash value of this object as a (lowercase) hexadecimal string"""
+        retval = b2a_hex(self.digest())
+        assert len(retval) == 64
+        if sys.version_info[0] == 2:
+            return retval
+        else:
+            return retval.decode()
+
+    # PEP 247 "update" method
+    def update(self, data):
+        self._h.update(data)
+
+# PEP 247 module-level "digest_size" variable
+digest_size = _SHAd256.digest_size
+
+# PEP 247 module-level "new" function
+def new(data=None):
+    """Return a new SHAd256 hashing object"""
+    if not data:
+        data=b("")
+    sha = _SHAd256(_SHAd256._internal, SHA256.new(data))
+    sha.new = globals()['new']
+    return sha
+
+# vim:set ts=4 sw=4 sts=4 expandtab: