[pycrypto] DES/DES3/XOR/etc removal

Thomas Dixon reikon at reikon.us
Wed Apr 22 15:05:20 CST 2009

Tzury Bar Yochay wrote:
> please keep the DES3 and XOR.
> we use them and need them in our ongoing projects
> On Wed, Apr 22, 2009 at 8:23 PM, Jean-Paul Calderone
> <exarkun at twistedmatrix.com <mailto:exarkun at twistedmatrix.com>> wrote:
>     Hello,
>     Someone pointed out that XOR and several other ciphers [1] have been
>     removed from PyCrypto.  This has the consequence that Twisted Conch,
>     and SSH client and server implementation which depends on PyCrypto,
>     no longer works with the latest development version of PyCrypto, and
>     I assume that when the next release of PyCrypto is made, Conch also
>     won't work with that.
>     I'm curious how important backwards compatibility is deemed with the
>     new PyCrypto development going on.  A change like the one referenced
>     above is going to break users of PyCrypto (and that seems like it is
>     really obvious, to me - as opposed to a change which only accidentally
>     breaks applications).  The added maintenance burden this causes makes
>     PyCrypto less attractive (one nice thing about PyCrypto having been
>     unmaintained for a long time is that Conch's use of it stayed as
>     correct (or incorrect) as it was when it was written).  Basically, the
>     question is whether I should expect more PyCrypto changes like this
>     as development proceeds, or whether I can make the argument that
>     backwards
>     compatibility is a *good* thing compelling.
>     Of course it's one thing to say "more backwards compatibility please".
>     Actually deciding how that can be accomplished while allowing
>     development
>     to proceed in a useful direction is another.  However, I'm
>     intentionally
>     omitting details of that discussion from this message to keep things
>     simple.  I'm convinced that some degree of backwards compatibility is
>     always possible, regardless of the changes desired, so the details
>     of how
>     it works aren't as important as deciding whether backwards
>     compatibility
>     will be maintained.
>     So, what do you say?  Can we decide that backwards compatibility
>     is a good
>     thing?
>     Jean-Paul
>     [1] -
>     http://gitweb.pycrypto.org/?p=crypto/pycrypto-2.x.git;a=commit;h=5b5b496c0f81f3595d0aebb8da5196492abae429
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Personally, if Dwayne has decided to remove Blowfish, DES, 3DES, RC5,
IDEA, and XOR, then I agree with that decision completely. From a legal
and security standpoint, it makes perfect sense. There's also nothing to
say that Dwayne won't add different implementations of some of these
algorithms back into PyCrypto's offerings at a later date. Remember:
Those who will primarily suffer from a software developer's laziness are
their users.


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