add memory limit check for scrypt (#3328)
* add memory limit check for scrypt
fixes #3323
* test a pass
* move _MEM_LIMIT to the scrypt module
diff --git a/src/cryptography/hazmat/backends/openssl/backend.py b/src/cryptography/hazmat/backends/openssl/backend.py
index 76ecc08..397a021 100644
--- a/src/cryptography/hazmat/backends/openssl/backend.py
+++ b/src/cryptography/hazmat/backends/openssl/backend.py
@@ -9,7 +9,6 @@
import collections
import contextlib
import itertools
-import sys
from contextlib import contextmanager
import six
@@ -59,6 +58,7 @@
from cryptography.hazmat.primitives.ciphers.modes import (
CBC, CFB, CFB8, CTR, ECB, GCM, OFB
)
+from cryptography.hazmat.primitives.kdf import scrypt
_MemoryBIO = collections.namedtuple("_MemoryBIO", ["bio", "char_ptr"])
@@ -1833,9 +1833,10 @@
def derive_scrypt(self, key_material, salt, length, n, r, p):
buf = self._ffi.new("unsigned char[]", length)
- res = self._lib.EVP_PBE_scrypt(key_material, len(key_material), salt,
- len(salt), n, r, p, sys.maxsize // 2,
- buf, length)
+ res = self._lib.EVP_PBE_scrypt(
+ key_material, len(key_material), salt, len(salt), n, r, p,
+ scrypt._MEM_LIMIT, buf, length
+ )
self.openssl_assert(res == 1)
return self._ffi.buffer(buf)[:]
diff --git a/src/cryptography/hazmat/primitives/kdf/scrypt.py b/src/cryptography/hazmat/primitives/kdf/scrypt.py
index 2093540..77dcf9a 100644
--- a/src/cryptography/hazmat/primitives/kdf/scrypt.py
+++ b/src/cryptography/hazmat/primitives/kdf/scrypt.py
@@ -4,6 +4,8 @@
from __future__ import absolute_import, division, print_function
+import sys
+
from cryptography import utils
from cryptography.exceptions import (
AlreadyFinalized, InvalidKey, UnsupportedAlgorithm, _Reasons
@@ -13,6 +15,11 @@
from cryptography.hazmat.primitives.kdf import KeyDerivationFunction
+# This is used by the scrypt tests to skip tests that require more memory
+# than the MEM_LIMIT
+_MEM_LIMIT = sys.maxsize // 2
+
+
@utils.register_interface(KeyDerivationFunction)
class Scrypt(object):
def __init__(self, salt, length, n, r, p, backend):
diff --git a/tests/hazmat/primitives/test_scrypt.py b/tests/hazmat/primitives/test_scrypt.py
index 49b304e..87aee1f 100644
--- a/tests/hazmat/primitives/test_scrypt.py
+++ b/tests/hazmat/primitives/test_scrypt.py
@@ -14,7 +14,7 @@
AlreadyFinalized, InvalidKey, UnsupportedAlgorithm
)
from cryptography.hazmat.backends.interfaces import ScryptBackend
-from cryptography.hazmat.primitives.kdf.scrypt import Scrypt
+from cryptography.hazmat.primitives.kdf.scrypt import Scrypt, _MEM_LIMIT
from tests.utils import load_nist_vectors, load_vectors_from_file
@@ -22,10 +22,30 @@
os.path.join("KDF", "scrypt.txt"), load_nist_vectors)
+def _skip_if_memory_limited(memory_limit, params):
+ # Memory calc adapted from OpenSSL (URL split over 2 lines, thanks PEP8)
+ # https://github.com/openssl/openssl/blob/6286757141a8c6e14d647ec733634a
+ # e0c83d9887/crypto/evp/scrypt.c#L189-L221
+ blen = int(params["p"]) * 128 * int(params["r"])
+ vlen = 32 * int(params["r"]) * (int(params["n"]) + 2) * 4
+ memory_required = blen + vlen
+ if memory_limit < memory_required:
+ pytest.skip("Test exceeds Scrypt memory limit. "
+ "This is likely a 32-bit platform.")
+
+
+def test_memory_limit_skip():
+ with pytest.raises(pytest.skip.Exception):
+ _skip_if_memory_limited(1000, {"p": 16, "r": 64, "n": 1024})
+
+ _skip_if_memory_limited(2 ** 31, {"p": 16, "r": 64, "n": 1024})
+
+
@pytest.mark.requires_backend_interface(interface=ScryptBackend)
class TestScrypt(object):
@pytest.mark.parametrize("params", vectors)
def test_derive(self, backend, params):
+ _skip_if_memory_limited(_MEM_LIMIT, params)
password = params["password"]
work_factor = int(params["n"])
block_size = int(params["r"])
@@ -77,6 +97,7 @@
@pytest.mark.parametrize("params", vectors)
def test_verify(self, backend, params):
+ _skip_if_memory_limited(_MEM_LIMIT, params)
password = params["password"]
work_factor = int(params["n"])
block_size = int(params["r"])