Add google-endpoints to third_party/.

third_party/google-endpoints/Crypto/Cipher/blockalgo.py

Index: third_party/google-endpoints/Crypto/Cipher/blockalgo.py
diff --git a/third_party/google-endpoints/Crypto/Cipher/blockalgo.py b/third_party/google-endpoints/Crypto/Cipher/blockalgo.py
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+# -*- coding: utf-8 -*-
+#
+#  Cipher/blockalgo.py 
+#
+# ===================================================================
+# 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.
+# ===================================================================
+"""Module with definitions common to all block ciphers."""
+
+import sys
+if sys.version_info[0] == 2 and sys.version_info[1] == 1:
+    from Crypto.Util.py21compat import *
+from Crypto.Util.py3compat import *
+
+#: *Electronic Code Book (ECB)*.
+#: This is the simplest encryption mode. Each of the plaintext blocks
+#: is directly encrypted into a ciphertext block, independently of
+#: any other block. This mode exposes frequency of symbols
+#: in your plaintext. Other modes (e.g. *CBC*) should be used instead.
+#:
+#: See `NIST SP800-38A`_ , Section 6.1 .
+#:
+#: .. _`NIST SP800-38A` : http://csrc.nist.gov/publications/nistpubs/800-38a/sp800-38a.pdf
+MODE_ECB = 1
+
+#: *Cipher-Block Chaining (CBC)*. Each of the ciphertext blocks depends
+#: on the current and all previous plaintext blocks. An Initialization Vector
+#: (*IV*) is required.
+#:
+#: The *IV* is a data block to be transmitted to the receiver.
+#: The *IV* can be made public, but it must be authenticated by the receiver and
+#: it should be picked randomly.
+#:
+#: See `NIST SP800-38A`_ , Section 6.2 .
+#:
+#: .. _`NIST SP800-38A` : http://csrc.nist.gov/publications/nistpubs/800-38a/sp800-38a.pdf
+MODE_CBC = 2
+
+#: *Cipher FeedBack (CFB)*. This mode is similar to CBC, but it transforms
+#: the underlying block cipher into a stream cipher. Plaintext and ciphertext
+#: are processed in *segments* of **s** bits. The mode is therefore sometimes
+#: labelled **s**-bit CFB. An Initialization Vector (*IV*) is required.
+#:
+#: When encrypting, each ciphertext segment contributes to the encryption of
+#: the next plaintext segment.
+#:
+#: This *IV* is a data block to be transmitted to the receiver.
+#: The *IV* can be made public, but it should be picked randomly.
+#: Reusing the same *IV* for encryptions done with the same key lead to
+#: catastrophic cryptographic failures.
+#:
+#: See `NIST SP800-38A`_ , Section 6.3 .
+#:
+#: .. _`NIST SP800-38A` : http://csrc.nist.gov/publications/nistpubs/800-38a/sp800-38a.pdf
+MODE_CFB = 3
+
+#: This mode should not be used.
+MODE_PGP = 4
+
+#: *Output FeedBack (OFB)*. This mode is very similar to CBC, but it
+#: transforms the underlying block cipher into a stream cipher.
+#: The keystream is the iterated block encryption of an Initialization Vector (*IV*).
+#:
+#: The *IV* is a data block to be transmitted to the receiver.
+#: The *IV* can be made public, but it should be picked randomly.
+#:
+#: Reusing the same *IV* for encryptions done with the same key lead to
+#: catastrophic cryptograhic failures.
+#:
+#: See `NIST SP800-38A`_ , Section 6.4 .
+#:
+#: .. _`NIST SP800-38A` : http://csrc.nist.gov/publications/nistpubs/800-38a/sp800-38a.pdf
+MODE_OFB = 5
+
+#: *CounTeR (CTR)*. This mode is very similar to ECB, in that
+#: encryption of one block is done independently of all other blocks.
+#: Unlike ECB, the block *position* contributes to the encryption and no
+#: information leaks about symbol frequency.
+#:
+#: Each message block is associated to a *counter* which must be unique
+#: across all messages that get encrypted with the same key (not just within
+#: the same message). The counter is as big as the block size.
+#:
+#: Counters can be generated in several ways. The most straightword one is
+#: to choose an *initial counter block* (which can be made public, similarly
+#: to the *IV* for the other modes) and increment its lowest **m** bits by
+#: one (modulo *2^m*) for each block. In most cases, **m** is chosen to be half
+#: the block size.
+#: 
+#: Reusing the same *initial counter block* for encryptions done with the same
+#: key lead to catastrophic cryptograhic failures.
+#:
+#: See `NIST SP800-38A`_ , Section 6.5 (for the mode) and Appendix B (for how
+#: to manage the *initial counter block*).
+#:
+#: .. _`NIST SP800-38A` : http://csrc.nist.gov/publications/nistpubs/800-38a/sp800-38a.pdf
+MODE_CTR = 6
+
+#: OpenPGP. This mode is a variant of CFB, and it is only used in PGP and OpenPGP_ applications.
+#: An Initialization Vector (*IV*) is required.
+#: 
+#: Unlike CFB, the IV is not transmitted to the receiver. Instead, the *encrypted* IV is.
+#: The IV is a random data block. Two of its bytes are duplicated to act as a checksum
+#: for the correctness of the key. The encrypted IV is therefore 2 bytes longer than
+#: the clean IV.
+#:
+#: .. _OpenPGP: http://tools.ietf.org/html/rfc4880
+MODE_OPENPGP = 7
+
+def _getParameter(name, index, args, kwargs, default=None):
+    """Find a parameter in tuple and dictionary arguments a function receives"""
+    param = kwargs.get(name)
+    if len(args)>index:
+        if param:
+            raise ValueError("Parameter '%s' is specified twice" % name)
+        param = args[index]
+    return param or default
+    
+class BlockAlgo:
+    """Class modelling an abstract block cipher."""
+
+    def __init__(self, factory, key, *args, **kwargs):
+        self.mode = _getParameter('mode', 0, args, kwargs, default=MODE_ECB)
+        self.block_size = factory.block_size
+        
+        if self.mode != MODE_OPENPGP:
+            self._cipher = factory.new(key, *args, **kwargs)
+            self.IV = self._cipher.IV
+        else:
+            # OPENPGP mode. For details, see 13.9 in RCC4880.
+            #
+            # A few members are specifically created for this mode:
+            #  - _encrypted_iv, set in this constructor
+            #  - _done_first_block, set to True after the first encryption
+            #  - _done_last_block, set to True after a partial block is processed
+            
+            self._done_first_block = False
+            self._done_last_block = False
+            self.IV = _getParameter('iv', 1, args, kwargs)
+            if not self.IV:
+                raise ValueError("MODE_OPENPGP requires an IV")
+            
+            # Instantiate a temporary cipher to process the IV
+            IV_cipher = factory.new(key, MODE_CFB,
+                    b('\x00')*self.block_size,      # IV for CFB
+                    segment_size=self.block_size*8)
+           
+            # The cipher will be used for...
+            if len(self.IV) == self.block_size:
+                # ... encryption
+                self._encrypted_IV = IV_cipher.encrypt(
+                    self.IV + self.IV[-2:] +        # Plaintext
+                    b('\x00')*(self.block_size-2)   # Padding
+                    )[:self.block_size+2]
+            elif len(self.IV) == self.block_size+2:
+                # ... decryption
+                self._encrypted_IV = self.IV
+                self.IV = IV_cipher.decrypt(self.IV +   # Ciphertext
+                    b('\x00')*(self.block_size-2)       # Padding
+                    )[:self.block_size+2]
+                if self.IV[-2:] != self.IV[-4:-2]:
+                    raise ValueError("Failed integrity check for OPENPGP IV")
+                self.IV = self.IV[:-2]
+            else:
+                raise ValueError("Length of IV must be %d or %d bytes for MODE_OPENPGP"
+                    % (self.block_size, self.block_size+2))
+
+            # Instantiate the cipher for the real PGP data
+            self._cipher = factory.new(key, MODE_CFB,
+                self._encrypted_IV[-self.block_size:],
+                segment_size=self.block_size*8)
+
+    def encrypt(self, plaintext):
+        """Encrypt data with the key and the parameters set at initialization.
+        
+        The cipher object is stateful; encryption of a long block
+        of data can be broken up in two or more calls to `encrypt()`.
+        That is, the statement:
+            
+            >>> c.encrypt(a) + c.encrypt(b)
+
+        is always equivalent to:
+
+             >>> c.encrypt(a+b)
+
+        That also means that you cannot reuse an object for encrypting
+        or decrypting other data with the same key.
+
+        This function does not perform any padding.
+       
+         - For `MODE_ECB`, `MODE_CBC`, and `MODE_OFB`, *plaintext* length
+           (in bytes) must be a multiple of *block_size*.
+
+         - For `MODE_CFB`, *plaintext* length (in bytes) must be a multiple
+           of *segment_size*/8.
+
+         - For `MODE_CTR`, *plaintext* can be of any length.
+
+         - For `MODE_OPENPGP`, *plaintext* must be a multiple of *block_size*,
+           unless it is the last chunk of the message.
+
+        :Parameters:
+          plaintext : byte string
+            The piece of data to encrypt.
+        :Return:
+            the encrypted data, as a byte string. It is as long as
+            *plaintext* with one exception: when encrypting the first message
+            chunk with `MODE_OPENPGP`, the encypted IV is prepended to the
+            returned ciphertext.
+        """
+
+        if self.mode == MODE_OPENPGP:
+            padding_length = (self.block_size - len(plaintext) % self.block_size) % self.block_size
+            if padding_length>0:
+                # CFB mode requires ciphertext to have length multiple of block size,
+                # but PGP mode allows the last block to be shorter
+                if self._done_last_block:
+                    raise ValueError("Only the last chunk is allowed to have length not multiple of %d bytes",
+                        self.block_size)
+                self._done_last_block = True
+                padded = plaintext + b('\x00')*padding_length
+                res = self._cipher.encrypt(padded)[:len(plaintext)]
+            else:
+                res = self._cipher.encrypt(plaintext)
+            if not self._done_first_block:
+                res = self._encrypted_IV + res
+                self._done_first_block = True
+            return res
+
+        return self._cipher.encrypt(plaintext)
+
+    def decrypt(self, ciphertext):
+        """Decrypt data with the key and the parameters set at initialization.
+        
+        The cipher object is stateful; decryption of a long block
+        of data can be broken up in two or more calls to `decrypt()`.
+        That is, the statement:
+            
+            >>> c.decrypt(a) + c.decrypt(b)
+
+        is always equivalent to:
+
+             >>> c.decrypt(a+b)
+
+        That also means that you cannot reuse an object for encrypting
+        or decrypting other data with the same key.
+
+        This function does not perform any padding.
+       
+         - For `MODE_ECB`, `MODE_CBC`, and `MODE_OFB`, *ciphertext* length
+           (in bytes) must be a multiple of *block_size*.
+
+         - For `MODE_CFB`, *ciphertext* length (in bytes) must be a multiple
+           of *segment_size*/8.
+
+         - For `MODE_CTR`, *ciphertext* can be of any length.
+
+         - For `MODE_OPENPGP`, *plaintext* must be a multiple of *block_size*,
+           unless it is the last chunk of the message.
+
+        :Parameters:
+          ciphertext : byte string
+            The piece of data to decrypt.
+        :Return: the decrypted data (byte string, as long as *ciphertext*).
+        """
+        if self.mode == MODE_OPENPGP:
+            padding_length = (self.block_size - len(ciphertext) % self.block_size) % self.block_size
+            if padding_length>0:
+                # CFB mode requires ciphertext to have length multiple of block size,
+                # but PGP mode allows the last block to be shorter
+                if self._done_last_block:
+                    raise ValueError("Only the last chunk is allowed to have length not multiple of %d bytes",
+                        self.block_size)
+                self._done_last_block = True
+                padded = ciphertext + b('\x00')*padding_length
+                res = self._cipher.decrypt(padded)[:len(ciphertext)]
+            else:
+                res = self._cipher.decrypt(ciphertext)
+            return res
+
+        return self._cipher.decrypt(ciphertext)
+