chunked update_into (#5419)

* chunked update_into

* all pointer arithmetic all the time

* review feedback

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

@@ -17,6 +17,7 @@
 class _CipherContext(object):
     _ENCRYPT = 1
     _DECRYPT = 0
+    _MAX_CHUNK_SIZE = 2 ** 31
 
     def __init__(self, backend, cipher, mode, operation):
         self._backend = backend
@@ -124,25 +125,32 @@ def update(self, data):
         return bytes(buf[:n])
 
     def update_into(self, data, buf):
-        if len(buf) < (len(data) + self._block_size_bytes - 1):
+        total_data_len = len(data)
+        if len(buf) < (total_data_len + self._block_size_bytes - 1):
             raise ValueError(
                 "buffer must be at least {} 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)
-        )
+        data_processed = 0
+        total_out = 0
         outlen = self._backend._ffi.new("int *")
-        res = self._backend._lib.EVP_CipherUpdate(
-            self._ctx,
-            buf,
-            outlen,
-            self._backend._ffi.from_buffer(data),
-            len(data),
-        )
-        self._backend.openssl_assert(res != 0)
-        return outlen[0]
+        baseoutbuf = self._backend._ffi.from_buffer(buf)
+        baseinbuf = self._backend._ffi.from_buffer(data)
+
+        while data_processed != total_data_len:
+            outbuf = baseoutbuf + total_out
+            inbuf = baseinbuf + data_processed
+            inlen = min(self._MAX_CHUNK_SIZE, total_data_len - data_processed)
+
+            res = self._backend._lib.EVP_CipherUpdate(
+                self._ctx, outbuf, outlen, inbuf, inlen
+            )
+            self._backend.openssl_assert(res != 0)
+            data_processed += inlen
+            total_out += outlen[0]
+
+        return total_out
 
     def finalize(self):
         if (

tests/hazmat/primitives/test_ciphers.py

@@ -316,3 +316,20 @@ def test_update_into_buffer_too_small_gcm(self, backend):
         buf = bytearray(5)
         with pytest.raises(ValueError):
             encryptor.update_into(b"testing", buf)
+
+    def test_update_into_auto_chunking(self, backend, monkeypatch):
+        key = b"\x00" * 16
+        c = ciphers.Cipher(AES(key), modes.ECB(), backend)
+        encryptor = c.encryptor()
+        # Lower max chunk size so we can test chunking
+        monkeypatch.setattr(encryptor._ctx, "_MAX_CHUNK_SIZE", 40)
+        buf = bytearray(527)
+        pt = b"abcdefghijklmnopqrstuvwxyz012345" * 16  # 512 bytes
+        processed = encryptor.update_into(pt, buf)
+        assert processed == 512
+        decryptor = c.decryptor()
+        # Change max chunk size to verify alternate boundaries don't matter
+        monkeypatch.setattr(decryptor._ctx, "_MAX_CHUNK_SIZE", 73)
+        decbuf = bytearray(527)
+        decprocessed = decryptor.update_into(buf[:processed], decbuf)
+        assert decbuf[:decprocessed] == pt