Counter: Deprecate disable_shortcut; Remove __PCT_CTR_SHORTCUT__ entirely

The `disable_shortcut` option served as a workaround in case
`__PCT_CTR_SHORTCUT__` leaked through a wrapper object, but I don't
think anyone actually used it, and it was a bad idea to expose it as
part of the public API.

Now that we do strong type checking inside block_template.c, there
shoujld be no need to ever use this option.  It's now a no-op, retained
for backward compatibility only.  It will be removed in some future
version of PyCrypto.

1 files changed, 13 insertions, 7 deletions

diff --git a/lib/Crypto/Util/Counter.py b/lib/Crypto/Util/Counter.py
index 60e281c..2068fb3 100644
--- a/lib/Crypto/Util/Counter.py
+++ b/lib/Crypto/Util/Counter.py
@@ -57,11 +57,15 @@ if sys.version_info[0] == 2 and sys.version_info[1] == 1:
     from Crypto.Util.py21compat import *
 from Crypto.Util.py3compat import *
 
+from Crypto.pct_warnings import DisableShortcut_DeprecationWarning
 from Crypto.Util import _counter
 import struct
+import warnings
+
 
 # Factory function
-def new(nbits, prefix=b(""), suffix=b(""), initial_value=1, overflow=0, little_endian=False, allow_wraparound=False, disable_shortcut=False):
+_deprecated = "deprecated"
+def new(nbits, prefix=b(""), suffix=b(""), initial_value=1, overflow=0, little_endian=False, allow_wraparound=False, disable_shortcut=_deprecated):
     """Create a stateful counter block function suitable for CTR encryption modes.
 
     Each call to the function returns the next counter block.
@@ -89,10 +93,9 @@ def new(nbits, prefix=b(""), suffix=b(""), initial_value=1, overflow=0, little_e
         If True, the function will raise an *OverflowError* exception as soon
         as the counter wraps around. If False (default), the counter will
         simply restart from zero.
-      disable_shortcut : boolean
-        If True, do not make ciphers from `Crypto.Cipher` bypass the Python
-        layer when invoking the counter block function.
-        If False (default), bypass the Python layer.
+      disable_shortcut : deprecated
+        This option is a no-op for backward compatibility.  It will be removed
+        in a future version.  Don't use it.
     :Returns:
       The counter block function.
     """
@@ -109,10 +112,13 @@ def new(nbits, prefix=b(""), suffix=b(""), initial_value=1, overflow=0, little_e
 
     initval = _encode(initial_value, nbytes, little_endian)
 
+    if disable_shortcut is not _deprecated:  # exact object comparison
+        warnings.warn("disable_shortcut has no effect and is deprecated", DisableShortcut_DeprecationWarning)
+
     if little_endian:
-        return _counter._newLE(bstr(prefix), bstr(suffix), initval, allow_wraparound=allow_wraparound, disable_shortcut=disable_shortcut)
+        return _counter._newLE(bstr(prefix), bstr(suffix), initval, allow_wraparound=allow_wraparound)
     else:
-        return _counter._newBE(bstr(prefix), bstr(suffix), initval, allow_wraparound=allow_wraparound, disable_shortcut=disable_shortcut)
+        return _counter._newBE(bstr(prefix), bstr(suffix), initval, allow_wraparound=allow_wraparound)
 
 def _encode(n, nbytes, little_endian=False):
     retval = []