Add support for ChaCha20 with LibreSSL

src/_cffi_src/build_openssl.py

@@ -26,6 +26,7 @@
         "asn1",
         "bignum",
         "bio",
+        "chacha",
         "cmac",
         "crypto",
         "dh",

src/_cffi_src/openssl/chacha.py

@@ -0,0 +1,39 @@
+# This file is dual licensed under the terms of the Apache License, Version
+# 2.0, and the BSD License. See the LICENSE file in the root of this repository
+# for complete details.
+
+from __future__ import annotations
+
+INCLUDES = """
+#if CRYPTOGRAPHY_IS_LIBRESSL
+#include <openssl/chacha.h>
+#endif"""
+
+TYPES = """
+static const long Cryptography_HAS_CHACHA20_API;
+"""
+
+FUNCTIONS = """
+void Cryptography_CRYPTO_chacha_20(uint8_t *, const uint8_t *, size_t,
+                                   const uint8_t[32], const uint8_t[8],
+                                   uint64_t);
+"""
+
+CUSTOMIZATIONS = """
+#if CRYPTOGRAPHY_IS_LIBRESSL
+static const long Cryptography_HAS_CHACHA20_API = 1;
+#else
+static const long Cryptography_HAS_CHACHA20_API = 0;
+#endif
+
+#if CRYPTOGRAPHY_IS_LIBRESSL
+void Cryptography_CRYPTO_chacha_20(uint8_t *out, const uint8_t *in,
+                                   size_t in_len, const uint8_t key[32],
+                                   const uint8_t nonce[8], uint64_t counter) {
+    CRYPTO_chacha_20(out, in, in_len, key, nonce, counter);
+}
+#else
+void (*Cryptography_CRYPTO_chacha_20)(uint8_t *, const uint8_t *, size_t, const uint8_t[32],
+                                      const uint8_t[8], uint64_t) = NULL;
+#endif
+"""

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

@@ -12,7 +12,11 @@
 from cryptography import utils, x509
 from cryptography.exceptions import UnsupportedAlgorithm, _Reasons
 from cryptography.hazmat.backends.openssl import aead
-from cryptography.hazmat.backends.openssl.ciphers import _CipherContext
+from cryptography.hazmat.backends.openssl.ciphers import (
+    _CipherContext,
+    create_cipher_context,
+)
+from cryptography.hazmat.backends.openssl.ciphers import algorithms
 from cryptography.hazmat.backends.openssl.cmac import _CMACContext
 from cryptography.hazmat.backends.openssl.rsa import (
     _RSAPrivateKey,
@@ -226,6 +230,12 @@ def hmac_supported(self, algorithm: hashes.HashAlgorithm) -> bool:
         return self.hash_supported(algorithm)
 
     def cipher_supported(self, cipher: CipherAlgorithm, mode: Mode) -> bool:
+        # ChaCha20 is supported in LibreSSL by a different API than OpenSSL,
+        # so checking for the corresponding EVP_CIPHER is not useful
+        if (self._lib.CRYPTOGRAPHY_IS_LIBRESSL) and isinstance(
+            cipher, algorithms.ChaCha20
+        ):
+            return True
         if self._fips_enabled:
             # FIPS mode requires AES. TripleDES is disallowed/deprecated in
             # FIPS 140-3.
@@ -319,12 +329,12 @@ def _register_default_ciphers(self) -> None:
     def create_symmetric_encryption_ctx(
         self, cipher: CipherAlgorithm, mode: Mode
     ) -> _CipherContext:
-        return _CipherContext(self, cipher, mode, _CipherContext._ENCRYPT)
+        return create_cipher_context(self, cipher, mode, encrypt=True)
 
     def create_symmetric_decryption_ctx(
         self, cipher: CipherAlgorithm, mode: Mode
     ) -> _CipherContext:
-        return _CipherContext(self, cipher, mode, _CipherContext._DECRYPT)
+        return create_cipher_context(self, cipher, mode, encrypt=False)
 
     def pbkdf2_hmac_supported(self, algorithm: hashes.HashAlgorithm) -> bool:
         return self.hmac_supported(algorithm)

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

@@ -4,6 +4,7 @@
 
 from __future__ import annotations
 
+import abc
 import typing
 
 from cryptography.exceptions import InvalidTag, UnsupportedAlgorithm, _Reasons
@@ -14,7 +15,93 @@
     from cryptography.hazmat.backends.openssl.backend import Backend
 
 
-class _CipherContext:
+class _CipherContext(metaclass=abc.ABCMeta):
+    @abc.abstractmethod
+    def update(self, data: bytes) -> bytes:
+        """
+        Processes the provided bytes through the cipher and returns the results
+        as bytes.
+        """
+
+    @abc.abstractmethod
+    def update_into(self, data: bytes, buf: bytes) -> int:
+        """
+        Processes the provided bytes and writes the resulting data into the
+        provided buffer. Returns the number of bytes written.
+        """
+
+    @abc.abstractmethod
+    def finalize(self) -> bytes:
+        """
+        Returns the results of processing the final block as bytes.
+        """
+
+
+def create_cipher_context(
+    backend: Backend, cipher, mode, encrypt: bool
+) -> _CipherContext:
+    if (
+        isinstance(cipher, algorithms.ChaCha20)
+        and backend._lib.Cryptography_HAS_CHACHA20_API
+    ):
+        return _CipherContextChaCha(backend, cipher)
+    else:
+        operation = (
+            _CipherContextEVP._ENCRYPT
+            if encrypt
+            else _CipherContextEVP._DECRYPT
+        )
+        return _CipherContextEVP(backend, cipher, mode, operation)
+
+
+class _CipherContextChaCha(_CipherContext):
+    """
+    Cipher context specific to ChaCha20 under LibreSSL
+    """
+
+    def __init__(self, backend: Backend, cipher) -> None:
+        assert isinstance(cipher, algorithms.ChaCha20)
+        assert backend._lib.Cryptography_HAS_CHACHA20_API
+        self._backend = backend
+        self._cipher = cipher
+
+        # The ChaCha20 stream cipher. The key length is 256 bits, the IV is 128 bits long.
+        # The first 64 bits consists of a counter in little-endian order followed by a 64
+        # bit nonce.
+        self._counter = int.from_bytes(cipher.nonce[:8], byteorder="little")
+        self._iv_nonce = cipher.nonce[8:]
+
+    def update(self, data: bytes) -> bytes:
+        buf = bytearray(len(data))
+        n = self.update_into(data, buf)
+        return bytes(buf[:n])
+
+    def update_into(self, data: bytes, buf: bytes) -> int:
+        total_data_len = len(data)
+        if len(buf) < total_data_len:
+            raise ValueError(
+                "buffer must be at least {} bytes for this "
+                "payload".format(len(data))
+            )
+
+        baseoutbuf = self._backend._ffi.from_buffer(buf, require_writable=True)
+        baseinbuf = self._backend._ffi.from_buffer(data)
+
+        self._backend._lib.Cryptography_CRYPTO_chacha_20(
+            baseoutbuf,
+            baseinbuf,
+            total_data_len,
+            self._backend._ffi.from_buffer(self._cipher.key),
+            self._backend._ffi.from_buffer(self._iv_nonce),
+            self._counter,
+        )
+        return total_data_len
+
+    def finalize(self) -> bytes:
+        return bytes()
+
+
+class _CipherContextEVP(_CipherContext):
     _ENCRYPT = 1
     _DECRYPT = 0
     _MAX_CHUNK_SIZE = 2**30 - 1