Create ChaCha20.py

audit/ChaCha20.py

@@ -0,0 +1,287 @@
+# ===================================================================
+#
+# Copyright (c) 2014, Legrandin <helderijs@gmail.com>
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions
+# are met:
+#
+# 1. Redistributions of source code must retain the above copyright
+#    notice, this list of conditions and the following disclaimer.
+# 2. Redistributions in binary form must reproduce the above copyright
+#    notice, this list of conditions and the following disclaimer in
+#    the documentation and/or other materials provided with the
+#    distribution.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+# FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+# COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+# INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+# BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+# LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+# CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+# ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+# POSSIBILITY OF SUCH DAMAGE.
+# ===================================================================
+
+from Crypto.Random import get_random_bytes
+
+from Crypto.Util.py3compat import _copy_bytes
+from Crypto.Util._raw_api import (load_pycryptodome_raw_lib,
+                                  create_string_buffer,
+                                  get_raw_buffer, VoidPointer,
+                                  SmartPointer, c_size_t,
+                                  c_uint8_ptr, c_ulong,
+                                  is_writeable_buffer)
+
+_raw_chacha20_lib = load_pycryptodome_raw_lib("Crypto.Cipher._chacha20",
+                    """
+                    int chacha20_init(void **pState,
+                                      const uint8_t *key,
+                                      size_t keySize,
+                                      const uint8_t *nonce,
+                                      size_t nonceSize);
+
+                    int chacha20_destroy(void *state);
+
+                    int chacha20_encrypt(void *state,
+                                         const uint8_t in[],
+                                         uint8_t out[],
+                                         size_t len);
+
+                    int chacha20_seek(void *state,
+                                      unsigned long block_high,
+                                      unsigned long block_low,
+                                      unsigned offset);
+                    int hchacha20(  const uint8_t key[32],
+                                    const uint8_t nonce16[16],
+                                    uint8_t subkey[32]);
+                    """)
+
+
+def _HChaCha20(key, nonce):
+
+    assert(len(key) == 32)
+    assert(len(nonce) == 16)
+
+    subkey = bytearray(32)
+    result = _raw_chacha20_lib.hchacha20(
+                c_uint8_ptr(key),
+                c_uint8_ptr(nonce),
+                c_uint8_ptr(subkey))
+    if result:
+        raise ValueError("Error %d when deriving subkey with HChaCha20" % result)
+
+    return subkey
+
+
+class ChaCha20Cipher(object):
+    """ChaCha20 (or XChaCha20) cipher object.
+    Do not create it directly. Use :py:func:`new` instead.
+
+    :var nonce: The nonce with length 8, 12 or 24 bytes
+    :vartype nonce: bytes
+    """
+
+    block_size = 1
+
+    def __init__(self, key, nonce):
+        """Initialize a ChaCha20/XChaCha20 cipher object
+
+        See also `new()` at the module level."""
+
+        self.nonce = _copy_bytes(None, None, nonce)
+
+        # XChaCha20 requires a key derivation with HChaCha20
+        # See 2.3 in https://tools.ietf.org/html/draft-arciszewski-xchacha-03
+        if len(nonce) == 24:
+            key = _HChaCha20(key, nonce[:16])
+            nonce = b'\x00' * 4 + nonce[16:]
+            self._name = "XChaCha20"
+        else:
+            self._name = "ChaCha20"
+            nonce = self.nonce
+
+        self._next = ( self.encrypt, self.decrypt )
+
+        self._state = VoidPointer()
+        result = _raw_chacha20_lib.chacha20_init(
+                        self._state.address_of(),
+                        c_uint8_ptr(key),
+                        c_size_t(len(key)),
+                        nonce,
+                        c_size_t(len(nonce)))
+        if result:
+            raise ValueError("Error %d instantiating a %s cipher" % (result,
+                                                                     self._name))
+        self._state = SmartPointer(self._state.get(),
+                                   _raw_chacha20_lib.chacha20_destroy)
+
+    def encrypt(self, plaintext, output=None):
+        """Encrypt a piece of data.
+
+        Args:
+          plaintext(bytes/bytearray/memoryview): The data to encrypt, of any size.
+        Keyword Args:
+          output(bytes/bytearray/memoryview): The location where the ciphertext
+            is written to. If ``None``, the ciphertext is returned.
+        Returns:
+          If ``output`` is ``None``, the ciphertext is returned as ``bytes``.
+          Otherwise, ``None``.
+        """
+
+        if self.encrypt not in self._next:
+            raise TypeError("Cipher object can only be used for decryption")
+        self._next = ( self.encrypt, )
+        return self._encrypt(plaintext, output)
+
+    def _encrypt(self, plaintext, output):
+        """Encrypt without FSM checks"""
+
+        if output is None:
+            ciphertext = create_string_buffer(len(plaintext))
+        else:
+            ciphertext = output
+
+            if not is_writeable_buffer(output):
+                raise TypeError("output must be a bytearray or a writeable memoryview")
+
+            if len(plaintext) != len(output):
+                raise ValueError("output must have the same length as the input"
+                                 "  (%d bytes)" % len(plaintext))
+
+        result = _raw_chacha20_lib.chacha20_encrypt(
+                                         self._state.get(),
+                                         c_uint8_ptr(plaintext),
+                                         c_uint8_ptr(ciphertext),
+                                         c_size_t(len(plaintext)))
+        if result:
+            raise ValueError("Error %d while encrypting with %s" % (result, self._name))
+
+        if output is None:
+            return get_raw_buffer(ciphertext)
+        else:
+            return None
+
+    def decrypt(self, ciphertext, output=None):
+        """Decrypt a piece of data.
+
+        Args:
+          ciphertext(bytes/bytearray/memoryview): The data to decrypt, of any size.
+        Keyword Args:
+          output(bytes/bytearray/memoryview): The location where the plaintext
+            is written to. If ``None``, the plaintext is returned.
+        Returns:
+          If ``output`` is ``None``, the plaintext is returned as ``bytes``.
+          Otherwise, ``None``.
+        """
+
+        if self.decrypt not in self._next:
+            raise TypeError("Cipher object can only be used for encryption")
+        self._next = ( self.decrypt, )
+
+        try:
+            return self._encrypt(ciphertext, output)
+        except ValueError as e:
+            raise ValueError(str(e).replace("enc", "dec"))
+
+    def seek(self, position):
+        """Seek to a certain position in the key stream.
+
+        Args:
+          position (integer):
+            The absolute position within the key stream, in bytes.
+        """
+
+        position, offset = divmod(position, 64)
+        block_low = position & 0xFFFFFFFF
+        block_high = position >> 32
+
+        result = _raw_chacha20_lib.chacha20_seek(
+                                                 self._state.get(),
+                                                 c_ulong(block_high),
+                                                 c_ulong(block_low),
+                                                 offset
+                                                 )
+        if result:
+            raise ValueError("Error %d while seeking with %s" % (result, self._name))
+
+
+def _derive_Poly1305_key_pair(key, nonce):
+    """Derive a tuple (r, s, nonce) for a Poly1305 MAC.
+
+    If nonce is ``None``, a new 12-byte nonce is generated.
+    """
+
+    if len(key) != 32:
+        raise ValueError("Poly1305 with ChaCha20 requires a 32-byte key")
+
+    if nonce is None:
+        padded_nonce = nonce = get_random_bytes(12)
+    elif len(nonce) == 8:
+        # See RFC7538, 2.6: [...] ChaCha20 as specified here requires a 96-bit
+        # nonce.  So if the provided nonce is only 64-bit, then the first 32
+        # bits of the nonce will be set to a constant number.
+        # This will usually be zero, but for protocols with multiple senders it may be
+        # different for each sender, but should be the same for all
+        # invocations of the function with the same key by a particular
+        # sender.
+        padded_nonce = b'\x00\x00\x00\x00' + nonce
+    elif len(nonce) == 12:
+        padded_nonce = nonce
+    else:
+        raise ValueError("Poly1305 with ChaCha20 requires an 8- or 12-byte nonce")
+
+    rs = new(key=key, nonce=padded_nonce).encrypt(b'\x00' * 32)
+    return rs[:16], rs[16:], nonce
+
+
+def new(**kwargs):
+    """Create a new ChaCha20 or XChaCha20 cipher
+
+    Keyword Args:
+        key (bytes/bytearray/memoryview): The secret key to use.
+            It must be 32 bytes long.
+        nonce (bytes/bytearray/memoryview): A mandatory value that
+            must never be reused for any other encryption
+            done with this key.
+
+            For ChaCha20, it must be 8 or 12 bytes long.
+
+            For XChaCha20, it must be 24 bytes long.
+
+            If not provided, 8 bytes will be randomly generated
+            (you can find them back in the ``nonce`` attribute).
+
+    :Return: a :class:`Crypto.Cipher.ChaCha20.ChaCha20Cipher` object
+    """
+
+    try:
+        key = kwargs.pop("key")
+    except KeyError as e:
+        raise TypeError("Missing parameter %s" % e)
+
+    nonce = kwargs.pop("nonce", None)
+    if nonce is None:
+        nonce = get_random_bytes(8)
+
+    if len(key) != 32:
+        raise ValueError("ChaCha20/XChaCha20 key must be 32 bytes long")
+
+    if len(nonce) not in (8, 12, 24):
+        raise ValueError("Nonce must be 8/12 bytes(ChaCha20) or 24 bytes (XChaCha20)")
+
+    if kwargs:
+        raise TypeError("Unknown parameters: " + str(kwargs))
+
+    return ChaCha20Cipher(key, nonce)
+
+# Size of a data block (in bytes)
+block_size = 1
+
+# Size of a key (in bytes)
+key_size = 32