Index: tarfile.py
===================================================================
--- tarfile.py	(revision 46040)
+++ tarfile.py	(working copy)
@@ -283,6 +283,9 @@
 class StreamError(TarError):
     """Exception for unsupported operations on stream-like TarFiles."""
     pass
+class HeaderError(TarError):
+    """Exception for invalid headers."""
+    pass
 
 #---------------------------
 # internal stream interface
@@ -822,9 +825,9 @@
         """Construct a TarInfo object from a 512 byte string buffer.
         """
         if len(buf) != BLOCKSIZE:
-            raise ValueError("truncated header")
+            raise HeaderError("truncated header")
         if buf.count(NUL) == BLOCKSIZE:
-            raise ValueError("empty header")
+            raise HeaderError("empty header")
 
         tarinfo = cls()
         tarinfo.buf = buf
@@ -844,7 +847,7 @@
         tarinfo.prefix = buf[345:500]
 
         if tarinfo.chksum not in calc_chksums(buf):
-            raise ValueError("invalid header")
+            raise HeaderError("invalid header")
         return tarinfo
 
     def tobuf(self, posix=False):
@@ -1753,13 +1756,6 @@
 
             try:
                 tarinfo = TarInfo.frombuf(buf)
- 
-                # We shouldn't rely on this checksum, because some tar programs
-                # calculate it differently and it is merely validating the
-                # header block. We could just as well skip this part, which would
-                # have a slight effect on performance...
-                if tarinfo.chksum not in calc_chksums(buf):
-                    self._dbg(1, "tarfile: Bad Checksum %r" % tarinfo.name)
 
                 # Set the TarInfo object's offset to the current position of the
                 # TarFile and set self.offset to the position where the data blocks
@@ -1769,16 +1765,14 @@
 
                 tarinfo = self.proc_member(tarinfo)
 
-            except ValueError, e:
+            except HeaderError, e:
                 if self.ignore_zeros:
-                    self._dbg(2, "0x%X: empty or invalid block: %s" %
-                              (self.offset, e))
+                    self._dbg(2, "0x%X: %s" % (self.offset, e))
                     self.offset += BLOCKSIZE
                     continue
                 else:
                     if self.offset == 0:
-                        raise ReadError("empty, unreadable or compressed "
-                                        "file: %s" % e)
+                        raise ReadError(str(e))
                     return None
             break