From 6178061e1b062972612bbc231e20db8a73a5673b Mon Sep 17 00:00:00 2001
From: Philipp Gesang <philipp.gesang@intra2net.com>
Date: Fri, 24 Mar 2017 12:20:45 +0100
Subject: [PATCH] implement encryption passthrough mode

---
 deltatar/crypto.py |   93 +++++++++++++++++++++++++++++++--------------------
 1 files changed, 56 insertions(+), 37 deletions(-)

diff --git a/deltatar/crypto.py b/deltatar/crypto.py
index 984bcab..9c4823c 100755
--- a/deltatar/crypto.py
+++ b/deltatar/crypto.py
@@ -260,6 +260,22 @@ def tag_read_stream (source):
 
 
 ###############################################################################
+## passthrough / null encryption
+###############################################################################
+
+class PassthroughCipher (object):
+
+    tag = struct.pack ("<QQ", 0, 0)
+
+    def __init__          (self)    : pass
+
+    def update            (self, b) : return b
+
+    def finalize          (self, )  : return b""
+
+    def finalize_with_tag (self, _) : return b""
+
+###############################################################################
 ## convenience wrapper
 ###############################################################################
 
@@ -313,7 +329,7 @@ class Crypto (object):
     """
     Encryption context to remain alive throughout an entire tarfile pass.
     """
-    aes  = None
+    enc  = None
     nacl = None
     key  = None
     pfx  = None # 64 bit fixed parts of IV
@@ -327,6 +343,7 @@ class Crypto (object):
     state   = STATE_FRESH
     ctsize  = -1
     ptsize  = -1
+    paramversion = None
 
     def __init__ (self, *al, **akv):
         self.set_parameters (*al, **akv)
@@ -340,7 +357,7 @@ class Crypto (object):
         if paramversion is None and nacl is None:
             # postpone until first header is available
             return
-        kdf       = kdf_by_version (paramversion)
+        kdf = kdf_by_version (paramversion)
         if kdf is not None:
             self.key, self.nacl = kdf (password, nacl)
 
@@ -349,24 +366,27 @@ class Crypto (object):
         if self.pfx is None:
             self.pfx = os.urandom(8)
 
-        self.nacl         = nacl
         self.paramversion = paramversion
 
 
     def process (self, buf):
-        if self.aes is not None:
+        if self.enc is not None:
             self.stats ["in"] += len (buf)
-            out = self.aes.update (buf)
+            out = self.enc.update (buf)
             self.stats ["out"] += len (out)
             return out
         return b""
 
 
-    def next (self):
+    def next (self, password, paramversion, nacl):
         self.ctsize = 0
         self.ptsize = 0
         self.stats ["obj"] += 1
         self.state = STATE_LIVE
+        if (   self.paramversion != paramversion
+            or self.password     != password
+            or self.nacl         != nacl):
+            self.set_parameters (password, paramversion, nacl)
 
 
     def counters (self):
@@ -394,30 +414,33 @@ class Encrypt (Crypto):
         self.iv = self.iv_make()
         self.curobj = (filename, version, paramversion, nacl or self.nacl)
         self.cnt += 1
-        self.aes = Cipher \
-                        ( algorithms.AES (self.key)
-                        , modes.GCM (self.iv)
-                        , backend = default_backend ()) \
-                        .encryptor ()
-        # XXX figure out what we want for AAD. Filename (not known to stream)?
-        #     Size?
-        #aad = "%s" % filename
-        #self.aes.authenticate_additional_data (str.encode (aad))
-
+        defs = ENCRYPTION_PARAMETERS.get(paramversion)
+        enc = defs ["enc"]
+        if enc == "aes-gcm":
+            self.enc = Cipher \
+                            ( algorithms.AES (self.key)
+                            , modes.GCM (self.iv)
+                            , backend = default_backend ()) \
+                            .encryptor ()
+        elif enc == "passthrough":
+            self.enc = PassthroughCipher ()
+        else:
+            raise Exception ("XXX garbage encryption parameter %d → %r"
+                             % (paramversion, enc))
         self.hdrdum = hdr_make_dummy (filename)
-        super().next ()
+        super().next (self.password, paramversion, nacl)
         return self.hdrdum
 
 
     def done (self, cmpdata):
         if cmpdata != self.hdrdum:
             raise Exception ("XXX bad sync for writing header") ## we need to converge on a sensible error handling strategy
-        data = self.aes.finalize ()
+        data = self.enc.finalize ()
         self.stats ["out"] += len (data)
         self.ctsize += len (data)
         (filename, version, paramversion, nacl) = self.curobj
         ok, hdr = hdr_from_params (version, paramversion, nacl, self.iv,
-                                   self.ctsize, self.aes.tag)
+                                   self.ctsize, self.enc.tag)
         if ok is False:
             raise Exception ("XXX error constructing header: %r" % hdr) ## we need to converge on a sensible error handling strategy
         self.state = STATE_DEAD
@@ -442,34 +465,30 @@ class Decrypt (Crypto):
 
     def next (self, hdr):
         if self.key is None:
-            super().__init__ (self.password, hdr ["paramversion"], hdr ["nacl"])
+            super().next (self.password, hdr ["paramversion"], hdr ["nacl"])
         self.cnt += 1
         iv = hdr ["iv"]
         self.tag = hdr ["tag"]
-        self.aes = Cipher \
-                        ( algorithms.AES (self.key)
-                        , modes.GCM (hdr["iv"], tag=self.tag)
-                        , backend = default_backend ()) \
-                        . decryptor ()
-        # XXX figure out what we want for AAD. Filename (not known to stream)?
-        #     Size?
-        #self.aes.authenticate_additional_data (str.encode (aad))
-
-    def next_in_source (self, tarinfo, source):
-        ok, hdr = hdr_read_stream (source)
-        if ok is False:
-            raise DecryptionError("Irrecoverable error reading header from "
-                                  "%r" % source)
-        return self.next(hdr)
+        if enc == "aes-gcm":
+            self.enc = Cipher \
+                            ( algorithms.AES (self.key)
+                            , modes.GCM (hdr["iv"], tag=self.tag)
+                            , backend = default_backend ()) \
+                            . decryptor ()
+        elif enc == "passthrough":
+            self.enc = PassthroughCipher ()
+        else:
+            raise Exception ("XXX garbage encryption parameter %d → %r"
+                             % (paramversion, enc))
 
 
     def done (self, tag=None):
         data = b""
         try:
             if tag is None:
-                ret, data = True, self.aes.finalize ()
+                ret, data = True, self.enc.finalize ()
             else:
-                ret, data = self.aes.finalize_with_tag (self.tag)
+                ret, data = self.enc.finalize_with_tag (self.tag)
         except crypto.cryptography.exceptions.InvalidTag as exn:
             return False, repr (exn)
         self.stats ["out"] += len (data)
-- 
1.7.1