overwrite buffers that may contain sensitive data

also reduce the amount of memory copying that we do

6 files changed, 236 insertions, 128 deletions

diff --git a/python/Makefile b/python/Makefile
index a19c4f8..5da703a 100644
--- a/python/Makefile
+++ b/python/Makefile
@@ -3,6 +3,8 @@ all: olm-python2 olm-python3
 include/olm/olm.h: ../include/olm/olm.h ../include/olm/inbound_group_session.h ../include/olm/outbound_group_session.h
 	mkdir -p include/olm
 	$(CPP) -I dummy -I ../include ../include/olm/olm.h -o include/olm/olm.h
+# add memset to the header so that we can use it to clear buffers
+	echo 'void *memset(void *s, int c, size_t n);' >> include/olm/olm.h
 
 olm-python2: include/olm/olm.h
 	DEVELOP=$(DEVELOP) python2 setup.py build
diff --git a/python/olm/_compat.py b/python/olm/_compat.py
index 8f1670d..91e4d1b 100644
--- a/python/olm/_compat.py
+++ b/python/olm/_compat.py
@@ -26,6 +26,16 @@ except ImportError:  # pragma: no cover
     URANDOM = urandom  # type: ignore
 
 
+def to_bytearray(string):
+    # type: (AnyStr) -> bytes
+    if isinstance(string, bytes):
+        return bytearray(string)
+    elif isinstance(string, str):
+        return bytearray(string, "utf-8")
+
+    raise TypeError("Invalid type {}".format(type(string)))
+
+
 def to_bytes(string):
     # type: (AnyStr) -> bytes
     if isinstance(string, bytes):
diff --git a/python/olm/account.py b/python/olm/account.py
index 1dba96d..8455655 100644
--- a/python/olm/account.py
+++ b/python/olm/account.py
@@ -37,7 +37,7 @@ from future.utils import bytes_to_native_str
 # pylint: disable=no-name-in-module
 from _libolm import ffi, lib  # type: ignore
 
-from ._compat import URANDOM, to_bytes
+from ._compat import URANDOM, to_bytearray
 from ._finalize import track_for_finalization
 
 # This is imported only for type checking purposes
@@ -82,12 +82,12 @@ class Account(object):
 
         random_length = lib.olm_create_account_random_length(self._account)
         random = URANDOM(random_length)
-        random_buffer = ffi.new("char[]", random)
 
         self._check_error(
-            lib.olm_create_account(self._account, random_buffer,
+            lib.olm_create_account(self._account, ffi.from_buffer(random),
                                    random_length))
 
+
     def _check_error(self, ret):
         # type: (int) -> None
         if ret != lib.olm_error():
@@ -111,15 +111,23 @@ class Account(object):
             passphrase(str, optional): The passphrase to be used to encrypt
                 the account.
         """
-        byte_key = bytes(passphrase, "utf-8") if passphrase else b""
-        key_buffer = ffi.new("char[]", byte_key)
+        byte_key = bytearray(passphrase, "utf-8") if passphrase else b""
 
         pickle_length = lib.olm_pickle_account_length(self._account)
         pickle_buffer = ffi.new("char[]", pickle_length)
 
-        self._check_error(
-            lib.olm_pickle_account(self._account, key_buffer, len(byte_key),
-                                   pickle_buffer, pickle_length))
+        try:
+            self._check_error(
+                lib.olm_pickle_account(self._account,
+                                       ffi.from_buffer(byte_key),
+                                       len(byte_key),
+                                       pickle_buffer,
+                                       pickle_length))
+        finally:
+            # zero out copies of the passphrase
+            for i in range(0, len(byte_key)):
+                byte_key[i] = 0
+
         return ffi.unpack(pickle_buffer, pickle_length)
 
     @classmethod
@@ -143,15 +151,22 @@ class Account(object):
         if not pickle:
             raise ValueError("Pickle can't be empty")
 
-        byte_key = bytes(passphrase, "utf-8") if passphrase else b""
-        key_buffer = ffi.new("char[]", byte_key)
+        byte_key = bytearray(passphrase, "utf-8") if passphrase else b""
+        # copy because unpickle will destroy the buffer
         pickle_buffer = ffi.new("char[]", pickle)
 
         obj = cls.__new__(cls)
 
-        ret = lib.olm_unpickle_account(obj._account, key_buffer, len(byte_key),
-                                       pickle_buffer, len(pickle))
-        obj._check_error(ret)
+        try:
+            ret = lib.olm_unpickle_account(obj._account,
+                                           ffi.from_buffer(byte_key),
+                                           len(byte_key),
+                                           pickle_buffer,
+                                           len(pickle))
+            obj._check_error(ret)
+        finally:
+            for i in range(0, len(byte_key)):
+                byte_key[i] = 0
 
         return obj
 
@@ -178,14 +193,21 @@ class Account(object):
         Args:
             message(str): The message to sign.
         """
-        bytes_message = to_bytes(message)
+        bytes_message = to_bytearray(message)
         out_length = lib.olm_account_signature_length(self._account)
-        message_buffer = ffi.new("char[]", bytes_message)
         out_buffer = ffi.new("char[]", out_length)
 
-        self._check_error(
-            lib.olm_account_sign(self._account, message_buffer,
-                                 len(bytes_message), out_buffer, out_length))
+        try:
+            self._check_error(
+                lib.olm_account_sign(self._account,
+                                     ffi.from_buffer(bytes_message),
+                                     len(bytes_message), out_buffer,
+                                     out_length))
+        finally:
+            # clear out copies of the message, which may be plaintext
+            if bytes_message is not message:
+                for i in range(0, len(bytes_message)):
+                    bytes_message[i] = 0
 
         return bytes_to_native_str(ffi.unpack(out_buffer, out_length))
 
@@ -214,10 +236,10 @@ class Account(object):
         random_length = lib.olm_account_generate_one_time_keys_random_length(
             self._account, count)
         random = URANDOM(random_length)
-        random_buffer = ffi.new("char[]", random)
+
         self._check_error(
             lib.olm_account_generate_one_time_keys(
-                self._account, count, random_buffer, random_length))
+                self._account, count, ffi.from_buffer(random), random_length))
 
     @property
     def one_time_keys(self):
diff --git a/python/olm/group_session.py b/python/olm/group_session.py
index bbb5e56..814ce27 100644
--- a/python/olm/group_session.py
+++ b/python/olm/group_session.py
@@ -33,7 +33,7 @@ from future.utils import bytes_to_native_str
 # pylint: disable=no-name-in-module
 from _libolm import ffi, lib  # type: ignore
 
-from ._compat import URANDOM, to_bytes
+from ._compat import URANDOM, to_bytearray, to_bytes
 from ._finalize import track_for_finalization
 
 
@@ -78,12 +78,17 @@ class InboundGroupSession(object):
         if False:  # pragma: no cover
             self._session = self._session  # type: ffi.cdata
 
-        byte_session_key = to_bytes(session_key)
-
-        key_buffer = ffi.new("char[]", byte_session_key)
-        ret = lib.olm_init_inbound_group_session(
-            self._session, key_buffer, len(byte_session_key)
-        )
+        byte_session_key = to_bytearray(session_key)
+
+        try:
+            ret = lib.olm_init_inbound_group_session(
+                self._session,
+                ffi.from_buffer(byte_session_key), len(byte_session_key)
+            )
+        finally:
+            if byte_session_key is not session_key:
+                for i in range(0, len(byte_session_key)):
+                    byte_session_key[i] = 0
         self._check_error(ret)
 
     def pickle(self, passphrase=""):
@@ -98,19 +103,23 @@ class InboundGroupSession(object):
             passphrase(str, optional): The passphrase to be used to encrypt
                 the session.
         """
-        byte_passphrase = bytes(passphrase, "utf-8") if passphrase else b""
+        byte_passphrase = bytearray(passphrase, "utf-8") if passphrase else b""
 
-        passphrase_buffer = ffi.new("char[]", byte_passphrase)
         pickle_length = lib.olm_pickle_inbound_group_session_length(
             self._session)
         pickle_buffer = ffi.new("char[]", pickle_length)
 
-        ret = lib.olm_pickle_inbound_group_session(
-            self._session, passphrase_buffer, len(byte_passphrase),
-            pickle_buffer, pickle_length
-        )
-
-        self._check_error(ret)
+        try:
+            ret = lib.olm_pickle_inbound_group_session(
+                self._session,
+                ffi.from_buffer(byte_passphrase), len(byte_passphrase),
+                pickle_buffer, pickle_length
+            )
+            self._check_error(ret)
+        finally:
+            # clear out copies of the passphrase
+            for i in range(0, len(byte_passphrase)):
+                    byte_passphrase[i] = 0
 
         return ffi.unpack(pickle_buffer, pickle_length)
 
@@ -135,20 +144,25 @@ class InboundGroupSession(object):
         if not pickle:
             raise ValueError("Pickle can't be empty")
 
-        byte_passphrase = bytes(passphrase, "utf-8") if passphrase else b""
-        passphrase_buffer = ffi.new("char[]", byte_passphrase)
+        byte_passphrase = bytearray(passphrase, "utf-8") if passphrase else b""
+        # copy because unpickle will destroy the buffer
         pickle_buffer = ffi.new("char[]", pickle)
 
         obj = cls.__new__(cls)
 
-        ret = lib.olm_unpickle_inbound_group_session(
-            obj._session,
-            passphrase_buffer,
-            len(byte_passphrase),
-            pickle_buffer,
-            len(pickle)
-        )
-        obj._check_error(ret)
+        try:
+            ret = lib.olm_unpickle_inbound_group_session(
+                obj._session,
+                ffi.from_buffer(byte_passphrase),
+                len(byte_passphrase),
+                pickle_buffer,
+                len(pickle)
+            )
+            obj._check_error(ret)
+        finally:
+            # clear out copies of the passphrase
+            for i in range(0, len(byte_passphrase)):
+                    byte_passphrase[i] = 0
 
         return obj
 
@@ -189,12 +203,15 @@ class InboundGroupSession(object):
 
         byte_ciphertext = to_bytes(ciphertext)
 
+        # copy because max_plaintext_length will destroy the buffer
         ciphertext_buffer = ffi.new("char[]", byte_ciphertext)
 
         max_plaintext_length = lib.olm_group_decrypt_max_plaintext_length(
             self._session, ciphertext_buffer, len(byte_ciphertext)
         )
+        self._check_error(max_plaintext_length)
         plaintext_buffer = ffi.new("char[]", max_plaintext_length)
+        # copy because max_plaintext_length will destroy the buffer
         ciphertext_buffer = ffi.new("char[]", byte_ciphertext)
 
         message_index = ffi.new("uint32_t*")
@@ -206,10 +223,15 @@ class InboundGroupSession(object):
 
         self._check_error(plaintext_length)
 
-        return bytes_to_native_str(ffi.unpack(
+        plaintext = bytes_to_native_str(ffi.unpack(
             plaintext_buffer,
             plaintext_length
-        )), message_index[0]
+        ))
+
+        # clear out copies of the plaintext
+        lib.memset(plaintext_buffer, 0, max_plaintext_length)
+
+        return plaintext, message_index[0]
 
     @property
     def id(self):
@@ -281,15 +303,19 @@ class InboundGroupSession(object):
         """
         obj = cls.__new__(cls)
 
-        byte_session_key = to_bytes(session_key)
+        byte_session_key = to_bytearray(session_key)
 
-        key_buffer = ffi.new("char[]", byte_session_key)
-        ret = lib.olm_import_inbound_group_session(
-            obj._session,
-            key_buffer,
-            len(byte_session_key)
-        )
-        obj._check_error(ret)
+        try:
+            ret = lib.olm_import_inbound_group_session(
+                obj._session,
+                ffi.from_buffer(byte_session_key),
+                len(byte_session_key)
+            )
+            obj._check_error(ret)
+        finally:
+            if byte_session_key is not session_key:
+                for i in range(0, len(byte_session_key)):
+                    byte_session_key[i] = 0
 
         return obj
 
@@ -323,10 +349,9 @@ class OutboundGroupSession(object):
             self._session
         )
         random = URANDOM(random_length)
-        random_buffer = ffi.new("char[]", random)
 
         ret = lib.olm_init_outbound_group_session(
-            self._session, random_buffer, random_length
+            self._session, ffi.from_buffer(random), random_length
         )
         self._check_error(ret)
 
@@ -353,17 +378,23 @@ class OutboundGroupSession(object):
             passphrase(str, optional): The passphrase to be used to encrypt
                 the session.
         """
-        byte_passphrase = bytes(passphrase, "utf-8") if passphrase else b""
-        passphrase_buffer = ffi.new("char[]", byte_passphrase)
+        byte_passphrase = bytearray(passphrase, "utf-8") if passphrase else b""
         pickle_length = lib.olm_pickle_outbound_group_session_length(
             self._session)
         pickle_buffer = ffi.new("char[]", pickle_length)
 
-        ret = lib.olm_pickle_outbound_group_session(
-            self._session, passphrase_buffer, len(byte_passphrase),
-            pickle_buffer, pickle_length
-        )
-        self._check_error(ret)
+        try:
+            ret = lib.olm_pickle_outbound_group_session(
+                self._session,
+                ffi.from_buffer(byte_passphrase), len(byte_passphrase),
+                pickle_buffer, pickle_length
+            )
+            self._check_error(ret)
+        finally:
+            # clear out copies of the passphrase
+            for i in range(0, len(byte_passphrase)):
+                    byte_passphrase[i] = 0
+
         return ffi.unpack(pickle_buffer, pickle_length)
 
     @classmethod
@@ -387,20 +418,25 @@ class OutboundGroupSession(object):
         if not pickle:
             raise ValueError("Pickle can't be empty")
 
-        byte_passphrase = bytes(passphrase, "utf-8") if passphrase else b""
-        passphrase_buffer = ffi.new("char[]", byte_passphrase)
+        byte_passphrase = bytearray(passphrase, "utf-8") if passphrase else b""
+        # copy because unpickle will destroy the buffer
         pickle_buffer = ffi.new("char[]", pickle)
 
         obj = cls.__new__(cls)
 
-        ret = lib.olm_unpickle_outbound_group_session(
-            obj._session,
-            passphrase_buffer,
-            len(byte_passphrase),
-            pickle_buffer,
-            len(pickle)
-        )
-        obj._check_error(ret)
+        try:
+            ret = lib.olm_unpickle_outbound_group_session(
+                obj._session,
+                ffi.from_buffer(byte_passphrase),
+                len(byte_passphrase),
+                pickle_buffer,
+                len(pickle)
+            )
+            obj._check_error(ret)
+        finally:
+            # clear out copies of the passphrase
+            for i in range(0, len(byte_passphrase)):
+                    byte_passphrase[i] = 0
 
         return obj
 
@@ -414,21 +450,26 @@ class OutboundGroupSession(object):
             plaintext(str): A string that will be encrypted using the group
                 session.
         """
-        byte_plaintext = to_bytes(plaintext)
+        byte_plaintext = to_bytearray(plaintext)
         message_length = lib.olm_group_encrypt_message_length(
             self._session, len(byte_plaintext)
         )
 
         message_buffer = ffi.new("char[]", message_length)
 
-        plaintext_buffer = ffi.new("char[]", byte_plaintext)
+        try:
+            ret = lib.olm_group_encrypt(
+                self._session,
+                ffi.from_buffer(byte_plaintext), len(byte_plaintext),
+                message_buffer, message_length,
+            )
+            self._check_error(ret)
+        finally:
+            # clear out copies of plaintext
+            if byte_plaintext is not plaintext:
+                for i in range(0, len(byte_plaintext)):
+                    byte_plaintext[i] = 0
 
-        ret = lib.olm_group_encrypt(
-            self._session,
-            plaintext_buffer, len(byte_plaintext),
-            message_buffer, message_length,
-        )
-        self._check_error(ret)
         return bytes_to_native_str(ffi.unpack(message_buffer, message_length))
 
     @property
diff --git a/python/olm/session.py b/python/olm/session.py
index b123e8a..cba9be0 100644
--- a/python/olm/session.py
+++ b/python/olm/session.py
@@ -40,7 +40,7 @@ from future.utils import bytes_to_native_str
 # pylint: disable=no-name-in-module
 from _libolm import ffi, lib  # type: ignore
 
-from ._compat import URANDOM, to_bytes
+from ._compat import URANDOM, to_bytearray, to_bytes
 from ._finalize import track_for_finalization
 
 # This is imported only for type checking purposes
@@ -164,15 +164,22 @@ class Session(object):
             passphrase(str, optional): The passphrase to be used to encrypt
                 the session.
         """
-        byte_key = bytes(passphrase, "utf-8") if passphrase else b""
-        key_buffer = ffi.new("char[]", byte_key)
+        byte_key = bytearray(passphrase, "utf-8") if passphrase else b""
 
         pickle_length = lib.olm_pickle_session_length(self._session)
         pickle_buffer = ffi.new("char[]", pickle_length)
 
-        self._check_error(
-            lib.olm_pickle_session(self._session, key_buffer, len(byte_key),
-                                   pickle_buffer, pickle_length))
+        try:
+            self._check_error(
+                lib.olm_pickle_session(self._session,
+                                       ffi.from_buffer(byte_key),
+                                       len(byte_key),
+                                       pickle_buffer, pickle_length))
+        finally:
+            # clear out copies of the passphrase
+            for i in range(0, len(byte_key)):
+                    byte_key[i] = 0
+
         return ffi.unpack(pickle_buffer, pickle_length)
 
     @classmethod
@@ -196,16 +203,23 @@ class Session(object):
         if not pickle:
             raise ValueError("Pickle can't be empty")
 
-        byte_key = bytes(passphrase, "utf-8") if passphrase else b""
-        key_buffer = ffi.new("char[]", byte_key)
+        byte_key = bytearray(passphrase, "utf-8") if passphrase else b""
+        # copy because unpickle will destroy the buffer
         pickle_buffer = ffi.new("char[]", pickle)
 
         session = cls.__new__(cls)
 
-        ret = lib.olm_unpickle_session(session._session, key_buffer,
-                                       len(byte_key), pickle_buffer,
-                                       len(pickle))
-        session._check_error(ret)
+        try:
+            ret = lib.olm_unpickle_session(session._session,
+                                           ffi.from_buffer(byte_key),
+                                           len(byte_key),
+                                           pickle_buffer,
+                                           len(pickle))
+            session._check_error(ret)
+        finally:
+            # clear out copies of the passphrase
+            for i in range(0, len(byte_key)):
+                    byte_key[i] = 0
 
         return session
 
@@ -217,29 +231,32 @@ class Session(object):
         Args:
             plaintext(str): The plaintext message that will be encrypted.
         """
-        byte_plaintext = to_bytes(plaintext)
+        byte_plaintext = to_bytearray(plaintext)
 
         r_length = lib.olm_encrypt_random_length(self._session)
         random = URANDOM(r_length)
-        random_buffer = ffi.new("char[]", random)
 
-        message_type = lib.olm_encrypt_message_type(self._session)
+        try:
+            message_type = lib.olm_encrypt_message_type(self._session)
 
-        self._check_error(message_type)
-
-        ciphertext_length = lib.olm_encrypt_message_length(
-            self._session, len(plaintext)
-        )
-        ciphertext_buffer = ffi.new("char[]", ciphertext_length)
+            self._check_error(message_type)
 
-        plaintext_buffer = ffi.new("char[]", byte_plaintext)
+            ciphertext_length = lib.olm_encrypt_message_length(
+                self._session, len(byte_plaintext)
+            )
+            ciphertext_buffer = ffi.new("char[]", ciphertext_length)
 
-        self._check_error(lib.olm_encrypt(
-            self._session,
-            plaintext_buffer, len(byte_plaintext),
-            random_buffer, r_length,
-            ciphertext_buffer, ciphertext_length,
-        ))
+            self._check_error(lib.olm_encrypt(
+                self._session,
+                ffi.from_buffer(byte_plaintext), len(byte_plaintext),
+                ffi.from_buffer(random), r_length,
+                ciphertext_buffer, ciphertext_length,
+            ))
+        finally:
+            # clear out copies of plaintext
+            if byte_plaintext is not plaintext:
+                for i in range(0, len(byte_plaintext)):
+                    byte_plaintext[i] = 0
 
         if message_type == lib.OLM_MESSAGE_TYPE_PRE_KEY:
             return OlmPreKeyMessage(
@@ -274,22 +291,34 @@ class Session(object):
             raise ValueError("Ciphertext can't be empty")
 
         byte_ciphertext = to_bytes(message.ciphertext)
+        # make a copy the ciphertext buffer, because
+        # olm_decrypt_max_plaintext_length wants to destroy something
         ciphertext_buffer = ffi.new("char[]", byte_ciphertext)
 
         max_plaintext_length = lib.olm_decrypt_max_plaintext_length(
             self._session, message.message_type, ciphertext_buffer,
             len(byte_ciphertext)
         )
+        self._check_error(max_plaintext_length)
         plaintext_buffer = ffi.new("char[]", max_plaintext_length)
+
+        # make a copy the ciphertext buffer, because
+        # olm_decrypt_max_plaintext_length wants to destroy something
         ciphertext_buffer = ffi.new("char[]", byte_ciphertext)
         plaintext_length = lib.olm_decrypt(
-            self._session, message.message_type, ciphertext_buffer,
-            len(byte_ciphertext), plaintext_buffer, max_plaintext_length
+            self._session, message.message_type,
+            ciphertext_buffer, len(byte_ciphertext),
+            plaintext_buffer, max_plaintext_length
         )
         self._check_error(plaintext_length)
-        return bytes_to_native_str(
+        plaintext = bytes_to_native_str(
             ffi.unpack(plaintext_buffer, plaintext_length))
 
+        # clear out copies of the plaintext
+        lib.memset(plaintext_buffer, 0, max_plaintext_length)
+
+        return plaintext
+
     @property
     def id(self):
         # type: () -> str
@@ -331,16 +360,16 @@ class Session(object):
         ret = None
 
         byte_ciphertext = to_bytes(message.ciphertext)
-
+        # make a copy, because olm_matches_inbound_session(_from) will distroy
+        # it
         message_buffer = ffi.new("char[]", byte_ciphertext)
 
         if identity_key:
             byte_id_key = to_bytes(identity_key)
-            identity_key_buffer = ffi.new("char[]", byte_id_key)
 
             ret = lib.olm_matches_inbound_session_from(
                 self._session,
-                identity_key_buffer, len(byte_id_key),
+                ffi.from_buffer(byte_id_key), len(byte_id_key),
                 message_buffer, len(byte_ciphertext)
             )
 
@@ -447,14 +476,11 @@ class OutboundSession(Session):
             self._session)
 
         random = URANDOM(session_random_length)
-        random_buffer = ffi.new("char[]", random)
-        identity_key_buffer = ffi.new("char[]", byte_id_key)
-        one_time_key_buffer = ffi.new("char[]", byte_one_time)
 
         self._check_error(lib.olm_create_outbound_session(
             self._session,
             account._account,
-            identity_key_buffer, len(byte_id_key),
-            one_time_key_buffer, len(byte_one_time),
-            random_buffer, session_random_length
+            ffi.from_buffer(byte_id_key), len(byte_id_key),
+            ffi.from_buffer(byte_one_time), len(byte_one_time),
+            ffi.from_buffer(random), session_random_length
         ))
diff --git a/python/olm/utility.py b/python/olm/utility.py
index 1c5c41d..0a64128 100644
--- a/python/olm/utility.py
+++ b/python/olm/utility.py
@@ -36,7 +36,7 @@ from typing import AnyStr, Type
 # pylint: disable=no-name-in-module
 from _libolm import ffi, lib  # type: ignore
 
-from ._compat import to_bytes
+from ._compat import to_bytearray, to_bytes
 from ._finalize import track_for_finalization
 
 
@@ -80,13 +80,20 @@ class _Utility(object):
             cls._allocate()
 
         byte_key = to_bytes(key)
-        byte_message = to_bytes(message)
+        byte_message = to_bytearray(message)
         byte_signature = to_bytes(signature)
 
-        cls._check_error(
-            lib.olm_ed25519_verify(cls._utility, byte_key, len(byte_key),
-                                   byte_message, len(byte_message),
-                                   byte_signature, len(byte_signature)))
+        try:
+            cls._check_error(
+                lib.olm_ed25519_verify(cls._utility, byte_key, len(byte_key),
+                                       ffi.from_buffer(byte_message),
+                                       len(byte_message),
+                                       byte_signature, len(byte_signature)))
+        finally:
+            # clear out copies of the message, which may be a plaintext
+            if byte_message is not message:
+                for i in range(0, len(byte_message)):
+                    byte_message[i] = 0
 
 
 def ed25519_verify(key, message, signature):