NIST SP 800-108 Counter Mode KDF (#2748)

* NIST SP 800-108 Counter Mode and Feedback Mode KDF

* CounterKDF unit tests

* Refactor to support multiple key based KDF modes.

* Extracting supported algorithms for KBKDF Counter Mode test vectors

* Adding support for different rlen and counter location in KBKDF

* support for multiple L lengths and 24 bit counter length.

* Adding KBKDF Documentation.

* Refactoring KBKDF to KBKDFHMAC to describe hash algorithm used.

1 files changed, 148 insertions, 0 deletions

diff --git a/src/cryptography/hazmat/primitives/kdf/kbkdf.py b/src/cryptography/hazmat/primitives/kdf/kbkdf.py
new file mode 100644
index 00000000..70a0fdc6
--- /dev/null
+++ b/src/cryptography/hazmat/primitives/kdf/kbkdf.py
@@ -0,0 +1,148 @@
+# This file is dual licensed under the terms of the Apache License, Version
+# 2.0, and the BSD License. See the LICENSE file in the root of this repository
+# for complete details.
+
+from __future__ import absolute_import, division, print_function
+
+from enum import Enum
+
+from six.moves import range
+
+from cryptography import utils
+from cryptography.exceptions import (
+    AlreadyFinalized, InvalidKey, UnsupportedAlgorithm, _Reasons
+)
+from cryptography.hazmat.backends.interfaces import HMACBackend
+from cryptography.hazmat.primitives import constant_time, hashes, hmac
+from cryptography.hazmat.primitives.kdf import KeyDerivationFunction
+
+
+class Mode(Enum):
+    CounterMode = "ctr"
+
+
+class CounterLocation(Enum):
+    BeforeFixed = "before_fixed"
+    AfterFixed = "after_fixed"
+
+
+@utils.register_interface(KeyDerivationFunction)
+class KBKDFHMAC(object):
+    def __init__(self, algorithm, mode, length, rlen, llen,
+                 location, label, context, fixed, backend):
+        if not isinstance(backend, HMACBackend):
+            raise UnsupportedAlgorithm(
+                "Backend object does not implement HMACBackend.",
+                _Reasons.BACKEND_MISSING_INTERFACE
+            )
+
+        if not isinstance(algorithm, hashes.HashAlgorithm):
+            raise UnsupportedAlgorithm(
+                "Algorithm supplied is not a supported hash algorithm.",
+                _Reasons.UNSUPPORTED_HASH
+            )
+
+        if not backend.hmac_supported(algorithm):
+            raise UnsupportedAlgorithm(
+                "Algorithm supplied is not a supported hmac algorithm.",
+                _Reasons.UNSUPPORTED_HASH
+            )
+
+        if not isinstance(mode, Mode):
+            raise TypeError("mode must be of type Mode")
+
+        if not isinstance(location, CounterLocation):
+            raise TypeError("location must be of type CounterLocation")
+
+        if (label or context) and fixed:
+            raise ValueError("When supplying fixed data, "
+                             "label and context are ignored.")
+
+        if rlen is None or not self._valid_byte_length(rlen):
+            raise ValueError("rlen must be between 1 and 4")
+
+        if llen is None and fixed is None:
+            raise ValueError("Please specify an llen")
+
+        if llen is not None and not isinstance(llen, int):
+            raise TypeError("llen must be an integer")
+
+        if label is None:
+            label = b''
+
+        if context is None:
+            context = b''
+
+        if (not isinstance(label, bytes) or
+                not isinstance(context, bytes)):
+            raise TypeError('label and context must be of type bytes')
+
+        self._algorithm = algorithm
+        self._mode = mode
+        self._length = length
+        self._rlen = rlen
+        self._llen = llen
+        self._location = location
+        self._label = label
+        self._context = context
+        self._backend = backend
+        self._used = False
+        self._fixed_data = fixed
+
+    def _valid_byte_length(self, value):
+        if not isinstance(value, int):
+            raise TypeError('value must be of type int')
+
+        value_bin = utils.int_to_bytes(1, value)
+        if not 1 <= len(value_bin) <= 4:
+            return False
+        return True
+
+    def derive(self, key_material):
+        if self._used:
+            raise AlreadyFinalized
+
+        if not isinstance(key_material, bytes):
+            raise TypeError('key_material must be bytes')
+        self._used = True
+
+        # inverse floor division (equivalent to ceiling)
+        rounds = -(-self._length // self._algorithm.digest_size)
+
+        output = [b'']
+
+        # For counter mode, the number of iterations shall not be
+        # larger than 2^r-1, where r ≤ 32 is the binary length of the counter
+        # This ensures that the counter values used as an input to the
+        # PRF will not repeat during a particular call to the KDF function.
+        r_bin = utils.int_to_bytes(1, self._rlen)
+        if rounds > pow(2, len(r_bin) * 8) - 1:
+            raise ValueError('There are too many iterations.')
+
+        for i in range(1, rounds + 1):
+            h = hmac.HMAC(key_material, self._algorithm, backend=self._backend)
+
+            counter = utils.int_to_bytes(i, self._rlen)
+            if self._location == CounterLocation.BeforeFixed:
+                h.update(counter)
+
+            h.update(self._generate_fixed_input())
+
+            if self._location == CounterLocation.AfterFixed:
+                h.update(counter)
+
+            output.append(h.finalize())
+
+        return b''.join(output)[:self._length]
+
+    def _generate_fixed_input(self):
+        if self._fixed_data and isinstance(self._fixed_data, bytes):
+            return self._fixed_data
+
+        l = utils.int_to_bytes(self._length * 8, self._llen)
+
+        return b"".join([self._label, b"\x00", self._context, l])
+
+    def verify(self, key_material, expected_key):
+        if not constant_time.bytes_eq(self.derive(key_material), expected_key):
+            raise InvalidKey