[ pycrypto-Patches-1255031 ] do CTR mode in pure C

Patches item #1255031, was opened at 2005-08-09 15:16
Message generated for change (Comment added) made by zooko
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Category: None
Group: None
Status: Open
Resolution: None
Priority: 5
Submitted By: Zooko O'Whielacronx (zooko)
Assigned to: Nobody/Anonymous (nobody)
Summary: do CTR mode in pure C

Initial Comment:
The design in which CTR mode calls a Python callable
for each block is very flexible, but suffers an obvious
performance cost.  After these patches, one can
optionally pass either a callable *or* a string of
block length.  If one passes a callable, then it
functions as before.  If one passes a string of length
block length, then it makes a copy of the contents of
the strings in an internal buffer, and increments that
value in C for each block.

This results in a nice speed-up, for example:

AES:
  ECB mode: 90841.10 K/sec
  CFB mode: 2380.59 K/sec
  CBC mode: 68653.57 K/sec
  PGP mode: 70991.19 K/sec
  OFB mode: 69941.49 K/sec
  CTR mode: 1251.37 K/sec
  CTR mode, variable length: 1728.07 K/sec
  CTR mode, fast increment: 68122.18 K/sec
  CTR mode, fast increment (slow decrypt): 2367.85 K/sec

That last line there is where it encrypts with the fast
incrementer and decrypts with the Python callback
incrementer to verify that the ctr increment is
computed the same way.

You can also browse and download these patches via my
web view:

https://yumyum.zooko.com:19144/cgi-bin/darcs.cgi/pycrypto-zookopatches/?c=patches

There are three patches in the attached file.


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>Comment By: Zooko O'Whielacronx (zooko)
Date: 2005-12-05 20:11

Message:
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Be sure and get the latest version from

https://yumyum.zooko.com:19144/cgi-bin/darcs.cgi/pycrypto-zookopatches/?c=patches

or

http://zooko.com/repos/pycrypto

or

https://yumyum.zooko.com:19144/pub/repos/pycrypto-zookopatches/

since earlier versions of this patch had a bug so that it
generated bad results if you crypted something that was not
a multiple of block length and then crypted something else
using the same cryptor object.

See the unit tests or the patches for details.


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Comment By: Zooko O'Whielacronx (zooko)
Date: 2005-08-17 15:27

Message:
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Okay, if you browse this patch server cgi script you can get
the fix:

https://yumyum.zooko.com:19144/cgi-bin/darcs.cgi/pycrypto-zookopatches/?c=patches

Or just use HTTP to fetch the files from

https://yumyum.zooko.com:19144/pub/repos/pycrypto-zookopatches

As you can see there are a few other patches for testing and
benchmarking in there.  The benchmarking requires the pyutil
library.

The benchmarking shows that this backwards-incompatible
change of eliminating the python callback and simplifying
the code gives a speedup of somewhere between 0 and 4%
depending on the exact usage.

(You could also keep the speedup and keep the optional
backwards-compatible Python callback support, but you can't
keep all three of the speedup, the
optional-backwards-compatible Python callback support, and
the simpler code.)

----------------------------------------------------------------------

Comment By: Zooko O'Whielacronx (zooko)
Date: 2005-08-17 12:07

Message:
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There's an issue in this patch -- it increments the counter
before encrypting, so if you initialize the counter with 0
then the first block will be encrypted with 1.

I'm fixing this issue, but my new patch is going to get rid
of the optional Python callback entirely.  (Maintaining both
ways to do it is complicating things.)



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