graciously handle GCM data length limit

[python-delta-tar] / deltatar / crypto.py

diff --git a/deltatar/crypto.py b/deltatar/crypto.py
index d01c20d..dab3f82 100755 (executable)
--- a/deltatar/crypto.py
+++ b/deltatar/crypto.py
@@ -219,16 +219,17 @@ FMT_I2N_HDR   = ("<"     # host byte order
                  "16s")  # GCM tag
 
 # aes+gcm
-AES_GCM_IV_LEN   = 12
-AES_GCM_MAX_SIZE = (1 << 36) - (1 << 5) # 2^39 - 2^8 b ≅ 64 GB
-AES_GCM_FMT_TAG  = "<16s"
+AES_GCM_MAX_SIZE              = (1 << 36) - (1 << 5) # 2^39 - 2^8 b ≅ 64 GB
+PDTCRYPT_MAX_OBJ_SIZE_DEFAULT = 63 * (1 << 30)       #                63 GB
+PDTCRYPT_MAX_OBJ_SIZE         = PDTCRYPT_MAX_OBJ_SIZE_DEFAULT
 
 # index and info files are written on-the fly while encrypting so their
 # counters must be available inadvance
-AES_GCM_IV_CNT_INFOFILE = 1 # constant
-AES_GCM_IV_CNT_INDEX    = AES_GCM_IV_CNT_INFOFILE + 1
-AES_GCM_IV_CNT_DATA     = AES_GCM_IV_CNT_INDEX    + 1 # also for multivolume
-AES_GCM_IV_CNT_MAX      = 0xffFFffFF
+AES_GCM_IV_CNT_INFOFILE     = 1 # constant
+AES_GCM_IV_CNT_INDEX        = AES_GCM_IV_CNT_INFOFILE + 1
+AES_GCM_IV_CNT_DATA         = AES_GCM_IV_CNT_INDEX    + 1 # also for multivolume
+AES_GCM_IV_CNT_MAX_DEFAULT  = 0xffFFffFF
+AES_GCM_IV_CNT_MAX          = AES_GCM_IV_CNT_MAX_DEFAULT
 
 
 ###############################################################################
@@ -522,12 +523,12 @@ class Crypto (object):
 
 
     def process (self, buf):
-        if self.enc is not None:
-            self.stats ["in"] += len (buf)
-            out = self.enc.update (buf)
-            self.stats ["out"] += len (out)
-            return out
-        return b""
+        if self.enc is None:
+            raise RuntimeError ("process: context not initialized")
+        self.stats ["in"] += len (buf)
+        out = self.enc.update (buf)
+        self.stats ["out"] += len (out)
+        return out
 
 
     def next (self, password, paramversion, nacl, iv):
@@ -617,10 +618,16 @@ class Encrypt (Crypto):
         return struct.pack(FMT_I2N_IV, self.fixed [-1], self.cnt)
 
 
-    def next (self, filename, counter=None):
-        if isinstance (filename, str) is False:
-            raise InvalidParameter ("next: filename must be a string, no %s"
-                                    % type (filename))
+    def next (self, filename=None, counter=None):
+        if filename is None:
+            if self.lastinfo is None:
+                raise InvalidParameter ("next: filename is mandatory for "
+                                        "first object")
+            filename, _dummy = self.lastinfo
+        else:
+            if isinstance (filename, str) is False:
+                raise InvalidParameter ("next: filename must be a string, no %s"
+                                        % type (filename))
         if counter is not None:
             if isinstance (counter, int) is False:
                 raise InvalidParameter ("next: the supplied counter is of "
@@ -651,6 +658,8 @@ class Encrypt (Crypto):
         if isinstance (cmpdata, bytes) is False:
             raise InvalidParameter ("done: comparison input expected as bytes, "
                                     "not %s" % type (cmpdata))
+        if self.lastinfo is None:
+            raise RuntimeError ("done: encryption context not initialized")
         filename, hdrdum = self.lastinfo
         if cmpdata != hdrdum:
             raise RuntimeError ("done: bad sync of header for object %d: "
@@ -671,10 +680,16 @@ class Encrypt (Crypto):
         if isinstance (buf, bytes) is False:
             raise InvalidParameter ("process: expected byte buffer, not %s"
                                     % type (buf))
-        self.ptsize += len (buf)
-        data = super().process (buf)
+        bsize = len (buf)
+        newptsize = self.ptsize + bsize
+        diff = newptsize - PDTCRYPT_MAX_OBJ_SIZE
+        if diff > 0:
+            bsize -= diff
+            newptsize = PDTCRYPT_MAX_OBJ_SIZE
+        self.ptsize = newptsize
+        data = super().process (buf [:bsize])
         self.ctsize += len (data)
-        return data
+        return bsize, data
 
 
 class Decrypt (Crypto):
@@ -807,16 +822,23 @@ class Decrypt (Crypto):
 ## testing helpers
 ###############################################################################
 
-def _testing_set_AES_GCM_IV_CNT_MAX (vow, n):
+def _patch_global (glob, vow, n=None):
     """
     Adapt upper file counter bound for testing IV logic. Completely unsafe.
     """
     assert vow == "I am fully aware that this will void my warranty."
-    global AES_GCM_IV_CNT_MAX
-    r = AES_GCM_IV_CNT_MAX
-    AES_GCM_IV_CNT_MAX = n
+    r = globals () [glob]
+    if n is None:
+        n = globals () [glob + "_DEFAULT"]
+    globals () [glob] = n
     return r
 
+_testing_set_AES_GCM_IV_CNT_MAX = \
+        partial (_patch_global, "AES_GCM_IV_CNT_MAX")
+
+_testing_set_PDTCRYPT_MAX_OBJ_SIZE = \
+        partial (_patch_global, "PDTCRYPT_MAX_OBJ_SIZE")
+
 ###############################################################################
 ## freestanding invocation
 ###############################################################################