add support for update_into on CipherContext

This allows you to provide your own buffer (like recv_into) to improve
performance when repeatedly calling encrypt/decrypt on large payloads.

docs/hazmat/primitives/symmetric-encryption.rst

@@ -456,6 +456,46 @@ Interfaces
         return bytes immediately, however in other modes it will return chunks
         whose size is determined by the cipher's block size.
 
+    .. method:: update_into(data, buf)
+
+        .. versionadded:: 1.6
+
+        .. warning::
+
+            This method allows you to avoid a memory copy by passing a writable
+            buffer and reading the resulting data. You are responsible for
+            correctly sizing the buffer and properly handling the data. This
+            method should only be used when extremely high performance is a
+            requirement.
+
+        :param bytes data: The data you wish to pass into the context.
+        :param buf: A writable Python buffer that the data will be written
+            into. This buffer should be ``n - 1`` bytes bigger than the size of
+            ``data`` where ``n`` is the block size (in bytes) of the cipher
+            and mode combination.
+        :return int: Number of bytes written.
+        :raises NotImplementedError: This is raised if the version of ``cffi``
+            used is too old (this can happen on older PyPy releases).
+        :raises ValueError: This is raised if the supplied buffer is too small.
+
+        .. doctest::
+
+            >>> import os
+            >>> from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
+            >>> from cryptography.hazmat.backends import default_backend
+            >>> backend = default_backend()
+            >>> key = os.urandom(32)
+            >>> iv = os.urandom(16)
+            >>> cipher = Cipher(algorithms.AES(key), modes.CBC(iv), backend=backend)
+            >>> encryptor = cipher.encryptor()
+            >>> buf = bytearray(31)
+            >>> len_encrypted = encryptor.update_into(b"a secret message", buf)
+            >>> ct = bytes(buf[:len_encrypted]) + encryptor.finalize()
+            >>> decryptor = cipher.decryptor()
+            >>> len_decrypted = decryptor.update_into(ct, buf)
+            >>> bytes(buf[:len_decrypted]) + decryptor.finalize()
+            'a secret message'
+
     .. method:: finalize()
 
         :return bytes: Returns the remainder of the data.

src/cryptography/hazmat/backends/commoncrypto/ciphers.py

@@ -4,6 +4,8 @@
 
 from __future__ import absolute_import, division, print_function
 
+import cffi
+
 from cryptography import utils
 from cryptography.exceptions import (
     InvalidTag, UnsupportedAlgorithm, _Reasons
@@ -86,6 +88,33 @@ def update(self, data):
         self._backend._check_cipher_response(res)
         return self._backend._ffi.buffer(buf)[:outlen[0]]
 
+    # cffi 1.7 supports from_buffer on bytearray, which is required. We can
+    # remove this check in the future when we raise our minimum PyPy version.
+    if utils._version_check(cffi.__version__, "1.7"):
+        def update_into(self, data, buf):
+            if len(buf) < (len(data) + self._byte_block_size - 1):
+                raise ValueError(
+                    "buffer must be at least {0} bytes for this "
+                    "payload".format(len(data) + self._byte_block_size - 1)
+                )
+            # Count bytes processed to handle block alignment.
+            self._bytes_processed += len(data)
+            outlen = self._backend._ffi.new("size_t *")
+            buf = self._backend._ffi.cast(
+                "unsigned char *", self._backend._ffi.from_buffer(buf)
+            )
+            res = self._backend._lib.CCCryptorUpdate(
+                self._ctx[0], data, len(data), buf,
+                len(data) + self._byte_block_size - 1, outlen)
+            self._backend._check_cipher_response(res)
+            return outlen[0]
+    else:
+        def update_into(self, data, buf):
+            raise NotImplementedError(
+                "update_into requires cffi 1.7+. To use this method please "
+                "update cffi."
+            )
+
     def finalize(self):
         # Raise error if block alignment is wrong.
         if self._bytes_processed % self._byte_block_size:
@@ -161,6 +190,33 @@ def update(self, data):
         self._backend._check_cipher_response(res)
         return self._backend._ffi.buffer(buf)[:]
 
+    # cffi 1.7 supports from_buffer on bytearray, which is required. We can
+    # remove this check in the future when we raise our minimum PyPy version.
+    if utils._version_check(cffi.__version__, "1.7"):
+        def update_into(self, data, buf):
+            if len(buf) < len(data):
+                raise ValueError(
+                    "buffer must be at least {0} bytes".format(len(data))
+                )
+
+            buf = self._backend._ffi.cast(
+                "unsigned char *", self._backend._ffi.from_buffer(buf)
+            )
+            args = (self._ctx[0], data, len(data), buf)
+            if self._operation == self._backend._lib.kCCEncrypt:
+                res = self._backend._lib.CCCryptorGCMEncrypt(*args)
+            else:
+                res = self._backend._lib.CCCryptorGCMDecrypt(*args)
+
+            self._backend._check_cipher_response(res)
+            return len(data)
+    else:
+        def update_into(self, data, buf):
+            raise NotImplementedError(
+                "update_into requires cffi 1.7+. To use this method please "
+                "update cffi."
+            )
+
     def finalize(self):
         # CommonCrypto has a yet another bug where you must make at least one
         # call to update. If you pass just AAD and call finalize without a call

src/cryptography/hazmat/backends/openssl/ciphers.py

@@ -4,6 +4,8 @@
 
 from __future__ import absolute_import, division, print_function
 
+import cffi
+
 from cryptography import utils
 from cryptography.exceptions import InvalidTag, UnsupportedAlgorithm, _Reasons
 from cryptography.hazmat.primitives import ciphers
@@ -109,6 +111,31 @@ def update(self, data):
         self._backend.openssl_assert(res != 0)
         return self._backend._ffi.buffer(buf)[:outlen[0]]
 
+    # cffi 1.7 supports from_buffer on bytearray, which is required. We can
+    # remove this check in the future when we raise our minimum PyPy version.
+    if utils._version_check(cffi.__version__, "1.7"):
+        def update_into(self, data, buf):
+            if len(buf) < (len(data) + self._block_size_bytes - 1):
+                raise ValueError(
+                    "buffer must be at least {0} bytes for this "
+                    "payload".format(len(data) + self._block_size_bytes - 1)
+                )
+
+            buf = self._backend._ffi.cast(
+                "unsigned char *", self._backend._ffi.from_buffer(buf)
+            )
+            outlen = self._backend._ffi.new("int *")
+            res = self._backend._lib.EVP_CipherUpdate(self._ctx, buf, outlen,
+                                                      data, len(data))
+            self._backend.openssl_assert(res != 0)
+            return outlen[0]
+    else:
+        def update_into(self, data, buf):
+            raise NotImplementedError(
+                "update_into requires cffi 1.7+. To use this method please "
+                "update cffi."
+            )
+
     def finalize(self):
         # OpenSSL 1.0.1 on Ubuntu 12.04 (and possibly other distributions)
         # appears to have a bug where you must make at least one call to update
@@ -196,6 +223,32 @@ def update(self, data):
         )
         return self._backend._ffi.buffer(buf)[:]
 
+    # cffi 1.7 supports from_buffer on bytearray, which is required. We can
+    # remove this check in the future when we raise our minimum PyPy version.
+    if utils._version_check(cffi.__version__, "1.7"):
+        def update_into(self, data, buf):
+            if len(buf) < len(data):
+                raise ValueError(
+                    "buffer must be at least {0} bytes".format(len(data))
+                )
+
+            buf = self._backend._ffi.from_buffer(buf)
+            self._backend._lib.AES_ctr128_encrypt(
+                data, buf, len(data), self._key, self._nonce,
+                self._ecount, self._num
+            )
+            # AES_ctr128_encrypt has no way to check for errors. Since the API
+            # says we return the bytes written and CTR mode is effectively a
+            # stream cipher we will always write as many bytes out as were
+            # passed in.
+            return len(data)
+    else:
+        def update_into(self, data, buf):
+            raise NotImplementedError(
+                "update_into requires cffi 1.7+. To use this method please "
+                "update cffi."
+            )
+
     def finalize(self):
         self._key = None
         self._ecount = None

src/cryptography/hazmat/primitives/ciphers/base.py

@@ -50,6 +50,13 @@ def update(self, data):
         as bytes.
         """
 
+    @abc.abstractmethod
+    def update_into(self, data, buf):
+        """
+        Processes the provided bytes and writes the resulting data into the
+        provided buffer. Returns the number of bytes written.
+        """
+
     @abc.abstractmethod
     def finalize(self):
         """
@@ -136,6 +143,11 @@ def update(self, data):
             raise AlreadyFinalized("Context was already finalized.")
         return self._ctx.update(data)
 
+    def update_into(self, data, buf):
+        if self._ctx is None:
+            raise AlreadyFinalized("Context was already finalized.")
+        return self._ctx.update_into(data, buf)
+
     def finalize(self):
         if self._ctx is None:
             raise AlreadyFinalized("Context was already finalized.")
@@ -154,20 +166,26 @@ def __init__(self, ctx):
         self._tag = None
         self._updated = False
 
-    def update(self, data):
+    def _check_limit(self, data_size):
         if self._ctx is None:
             raise AlreadyFinalized("Context was already finalized.")
         self._updated = True
-        self._bytes_processed += len(data)
+        self._bytes_processed += data_size
         if self._bytes_processed > self._ctx._mode._MAX_ENCRYPTED_BYTES:
             raise ValueError(
                 "{0} has a maximum encrypted byte limit of {1}".format(
                     self._ctx._mode.name, self._ctx._mode._MAX_ENCRYPTED_BYTES
                 )
             )
 
+    def update(self, data):
+        self._check_limit(len(data))
         return self._ctx.update(data)
 
+    def update_into(self, data, buf):
+        self._check_limit(len(data))
+        return self._ctx.update_into(data, buf)
+
     def finalize(self):
         if self._ctx is None:
             raise AlreadyFinalized("Context was already finalized.")

src/cryptography/utils.py

@@ -11,6 +11,8 @@
 import sys
 import warnings
 
+from pkg_resources import parse_version
+
 
 # the functions deprecated in 1.0 and 1.4 are on an arbitrarily extended
 # deprecation cycle and should not be removed until we agree on when that cycle
@@ -108,6 +110,11 @@ def bit_length(x):
         return len(bin(x)) - (2 + (x <= 0))
 
 
+def _version_check(version, required_version):
+    # This is used to check if we support update_into on CipherContext.
+    return parse_version(version) >= parse_version(required_version)
+
+
 class _DeprecatedValue(object):
     def __init__(self, value, message, warning_class):
         self.value = value

tests/hazmat/primitives/test_ciphers.py

@@ -5,17 +5,25 @@
 from __future__ import absolute_import, division, print_function
 
 import binascii
+import os
+
+import cffi
 
 import pytest
 
+from pkg_resources import parse_version
+
 from cryptography.exceptions import _Reasons
+from cryptography.hazmat.backends.interfaces import CipherBackend
 from cryptography.hazmat.primitives import ciphers
 from cryptography.hazmat.primitives.ciphers.algorithms import (
     AES, ARC4, Blowfish, CAST5, Camellia, IDEA, SEED, TripleDES
 )
 from cryptography.hazmat.primitives.ciphers.modes import ECB
 
-from ...utils import raises_unsupported_algorithm
+from ...utils import (
+    load_nist_vectors, load_vectors_from_file, raises_unsupported_algorithm
+)
 
 
 class TestAES(object):
@@ -133,3 +141,83 @@ def test_invalid_backend():
 
     with raises_unsupported_algorithm(_Reasons.BACKEND_MISSING_INTERFACE):
         ciphers.Cipher(AES(b"AAAAAAAAAAAAAAAA"), ECB, pretend_backend)
+
+
+@pytest.mark.skipif(
+    parse_version(cffi.__version__) < parse_version('1.7'),
+    reason="cffi version too old"
+)
+@pytest.mark.supported(
+    only_if=lambda backend: backend.cipher_supported(
+        AES(b"\x00" * 16), ECB()
+    ),
+    skip_message="Does not support AES ECB",
+)
+@pytest.mark.requires_backend_interface(interface=CipherBackend)
+class TestCipherUpdateInto(object):
+    @pytest.mark.parametrize(
+        "params",
+        load_vectors_from_file(
+            os.path.join("ciphers", "AES", "ECB", "ECBGFSbox128.rsp"),
+            load_nist_vectors
+        )
+    )
+    def test_update_into(self, params, backend):
+        key = binascii.unhexlify(params["key"])
+        pt = binascii.unhexlify(params["plaintext"])
+        ct = binascii.unhexlify(params["ciphertext"])
+        c = ciphers.Cipher(AES(key), ECB(), backend)
+        encryptor = c.encryptor()
+        buf = bytearray(len(pt) + 15)
+        res = encryptor.update_into(pt, buf)
+        assert res == len(pt)
+        assert bytes(buf)[:res] == ct
+
+    @pytest.mark.parametrize(
+        "params",
+        load_vectors_from_file(
+            os.path.join("ciphers", "AES", "ECB", "ECBGFSbox128.rsp"),
+            load_nist_vectors
+        )
+    )
+    def test_update_into_multiple_calls(self, params, backend):
+        key = binascii.unhexlify(params["key"])
+        pt = binascii.unhexlify(params["plaintext"])
+        ct = binascii.unhexlify(params["ciphertext"])
+        c = ciphers.Cipher(AES(key), ECB(), backend)
+        encryptor = c.encryptor()
+        buf = bytearray(len(pt) + 15)
+        res = encryptor.update_into(pt[:3], buf)
+        assert res == 0
+        res = encryptor.update_into(pt[3:], buf)
+        assert res == len(pt)
+        assert bytes(buf)[:res] == ct
+
+    def test_update_into_buffer_too_small(self, backend):
+        key = b"\x00" * 16
+        c = ciphers.Cipher(AES(key), ECB(), backend)
+        encryptor = c.encryptor()
+        buf = bytearray(16)
+        with pytest.raises(ValueError):
+            encryptor.update_into(b"testing", buf)
+
+
+@pytest.mark.skipif(
+    parse_version(cffi.__version__) >= parse_version('1.7'),
+    reason="cffi version too new"
+)
+@pytest.mark.supported(
+    only_if=lambda backend: backend.cipher_supported(
+        AES(b"\x00" * 16), ECB()
+    ),
+    skip_message="Does not support AES ECB",
+)
+@pytest.mark.requires_backend_interface(interface=CipherBackend)
+class TestCipherUpdateIntoUnsupported(object):
+    def test_cffi_too_old(self, backend):
+        key = b"\x00" * 16
+        c = ciphers.Cipher(AES(key), ECB(), backend)
+        encryptor = c.encryptor()
+        buf = bytearray(32)
+        with pytest.raises(NotImplementedError):
+            encryptor.update_into(b"\x00" * 16, buf)