Merge pull request #486 from reaperhulk/commoncrypto-cipher-backend

Add CommonCrypto cipher backend

1 files changed, 191 insertions, 1 deletions

diff --git a/cryptography/hazmat/backends/commoncrypto/backend.py b/cryptography/hazmat/backends/commoncrypto/backend.py
index 603edc40..2d142569 100644
--- a/cryptography/hazmat/backends/commoncrypto/backend.py
+++ b/cryptography/hazmat/backends/commoncrypto/backend.py
@@ -18,10 +18,16 @@ from collections import namedtuple
 from cryptography import utils
 from cryptography.exceptions import UnsupportedAlgorithm
 from cryptography.hazmat.backends.interfaces import (
-    HashBackend, HMACBackend,
+    HashBackend, HMACBackend, CipherBackend
 )
 from cryptography.hazmat.bindings.commoncrypto.binding import Binding
 from cryptography.hazmat.primitives import interfaces
+from cryptography.hazmat.primitives.ciphers.algorithms import (
+    AES, Blowfish, TripleDES, ARC4
+)
+from cryptography.hazmat.primitives.ciphers.modes import (
+    CBC, CTR, ECB, OFB, CFB
+)
 
 
 HashMethods = namedtuple(
@@ -29,6 +35,7 @@ HashMethods = namedtuple(
 )
 
 
+@utils.register_interface(CipherBackend)
 @utils.register_interface(HashBackend)
 @utils.register_interface(HMACBackend)
 class Backend(object):
@@ -42,6 +49,8 @@ class Backend(object):
         self._ffi = self._binding.ffi
         self._lib = self._binding.lib
 
+        self._cipher_registry = {}
+        self._register_default_ciphers()
         self._hash_mapping = {
             "md5": HashMethods(
                 "CC_MD5_CTX *", self._lib.CC_MD5_Init,
@@ -100,6 +109,187 @@ class Backend(object):
     def create_hmac_ctx(self, key, algorithm):
         return _HMACContext(self, key, algorithm)
 
+    def cipher_supported(self, cipher, mode):
+        try:
+            self._cipher_registry[type(cipher), type(mode)]
+        except KeyError:
+            return False
+        return True
+
+    def create_symmetric_encryption_ctx(self, cipher, mode):
+        return _CipherContext(self, cipher, mode, _CipherContext._ENCRYPT)
+
+    def create_symmetric_decryption_ctx(self, cipher, mode):
+        return _CipherContext(self, cipher, mode, _CipherContext._DECRYPT)
+
+    def _register_cipher_adapter(self, cipher_cls, cipher_const, mode_cls,
+                                 mode_const):
+        if (cipher_cls, mode_cls) in self._cipher_registry:
+            raise ValueError("Duplicate registration for: {0} {1}".format(
+                cipher_cls, mode_cls)
+            )
+        self._cipher_registry[cipher_cls, mode_cls] = (cipher_const,
+                                                       mode_const)
+
+    def _register_default_ciphers(self):
+        for mode_cls, mode_const in [
+            (CBC, self._lib.kCCModeCBC),
+            (ECB, self._lib.kCCModeECB),
+            (CFB, self._lib.kCCModeCFB),
+            (OFB, self._lib.kCCModeOFB),
+            (CTR, self._lib.kCCModeCTR)
+        ]:
+            self._register_cipher_adapter(
+                AES,
+                self._lib.kCCAlgorithmAES128,
+                mode_cls,
+                mode_const
+            )
+        for mode_cls, mode_const in [
+            (CBC, self._lib.kCCModeCBC),
+            (CFB, self._lib.kCCModeCFB),
+            (OFB, self._lib.kCCModeOFB),
+        ]:
+            self._register_cipher_adapter(
+                TripleDES,
+                self._lib.kCCAlgorithm3DES,
+                mode_cls,
+                mode_const
+            )
+        for mode_cls, mode_const in [
+            (CBC, self._lib.kCCModeCBC),
+            (ECB, self._lib.kCCModeECB),
+            (CFB, self._lib.kCCModeCFB),
+            (OFB, self._lib.kCCModeOFB)
+        ]:
+            self._register_cipher_adapter(
+                Blowfish,
+                self._lib.kCCAlgorithmBlowfish,
+                mode_cls,
+                mode_const
+            )
+        self._register_cipher_adapter(
+            ARC4,
+            self._lib.kCCAlgorithmRC4,
+            type(None),
+            self._lib.kCCModeRC4
+        )
+
+    def _check_response(self, response):
+        if response == self._lib.kCCSuccess:
+            return
+        elif response == self._lib.kCCAlignmentError:
+            # This error is not currently triggered due to a bug filed as
+            # rdar://15589470
+            raise ValueError(
+                "The length of the provided data is not a multiple of "
+                "the block length"
+            )
+        else:
+            raise SystemError(
+                "The backend returned an error. Code: {0}".format(response)
+            )
+
+
+def _release_cipher_ctx(ctx):
+    """
+    Called by the garbage collector and used to safely dereference and
+    release the context.
+    """
+    if ctx[0] != backend._ffi.NULL:
+        res = backend._lib.CCCryptorRelease(ctx[0])
+        backend._check_response(res)
+        ctx[0] = backend._ffi.NULL
+
+
+@utils.register_interface(interfaces.CipherContext)
+class _CipherContext(object):
+    _ENCRYPT = 0  # kCCEncrypt
+    _DECRYPT = 1  # kCCDecrypt
+
+    def __init__(self, backend, cipher, mode, operation):
+        self._backend = backend
+        self._cipher = cipher
+        self._mode = mode
+        self._operation = operation
+        # There is a bug in CommonCrypto where block ciphers do not raise
+        # kCCAlignmentError when finalizing if you supply non-block aligned
+        # data. To work around this we need to keep track of the block
+        # alignment ourselves, but only for alg+mode combos that require
+        # block alignment. OFB, CFB, and CTR make a block cipher algorithm
+        # into a stream cipher so we don't need to track them (and thus their
+        # block size is effectively 1 byte just like OpenSSL/CommonCrypto
+        # treat RC4 and other stream cipher block sizes).
+        # This bug has been filed as rdar://15589470
+        self._bytes_processed = 0
+        if (isinstance(cipher, interfaces.BlockCipherAlgorithm) and not
+                isinstance(mode, (OFB, CFB, CTR))):
+            self._byte_block_size = cipher.block_size // 8
+        else:
+            self._byte_block_size = 1
+
+        registry = self._backend._cipher_registry
+        try:
+            cipher_enum, mode_enum = registry[type(cipher), type(mode)]
+        except KeyError:
+            raise UnsupportedAlgorithm(
+                "cipher {0} in {1} mode is not supported "
+                "by this backend".format(
+                    cipher.name, mode.name if mode else mode)
+            )
+
+        ctx = self._backend._ffi.new("CCCryptorRef *")
+        ctx = self._backend._ffi.gc(ctx, _release_cipher_ctx)
+
+        if isinstance(mode, interfaces.ModeWithInitializationVector):
+            iv_nonce = mode.initialization_vector
+        elif isinstance(mode, interfaces.ModeWithNonce):
+            iv_nonce = mode.nonce
+        else:
+            iv_nonce = self._backend._ffi.NULL
+
+        if isinstance(mode, CTR):
+            mode_option = self._backend._lib.kCCModeOptionCTR_BE
+        else:
+            mode_option = 0
+
+        res = self._backend._lib.CCCryptorCreateWithMode(
+            operation,
+            mode_enum, cipher_enum,
+            self._backend._lib.ccNoPadding, iv_nonce,
+            cipher.key, len(cipher.key),
+            self._backend._ffi.NULL, 0, 0, mode_option, ctx)
+        self._backend._check_response(res)
+
+        self._ctx = ctx
+
+    def update(self, data):
+        # Count bytes processed to handle block alignment.
+        self._bytes_processed += len(data)
+        buf = self._backend._ffi.new(
+            "unsigned char[]", len(data) + self._byte_block_size - 1)
+        outlen = self._backend._ffi.new("size_t *")
+        res = self._backend._lib.CCCryptorUpdate(
+            self._ctx[0], data, len(data), buf,
+            len(data) + self._byte_block_size - 1, outlen)
+        self._backend._check_response(res)
+        return self._backend._ffi.buffer(buf)[:outlen[0]]
+
+    def finalize(self):
+        # Raise error if block alignment is wrong.
+        if self._bytes_processed % self._byte_block_size:
+            raise ValueError(
+                "The length of the provided data is not a multiple of "
+                "the block length"
+            )
+        buf = self._backend._ffi.new("unsigned char[]", self._byte_block_size)
+        outlen = self._backend._ffi.new("size_t *")
+        res = self._backend._lib.CCCryptorFinal(
+            self._ctx[0], buf, len(buf), outlen)
+        self._backend._check_response(res)
+        _release_cipher_ctx(self._ctx)
+        return self._backend._ffi.buffer(buf)[:outlen[0]]
+
 
 @utils.register_interface(interfaces.HashContext)
 class _HashContext(object):