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<H1>[pycrypto] RSA exportKey() changes set in stone for 2.7?</H1>
<B>Kurt Vogel</B>
<A HREF="mailto:pycrypto%40lists.dlitz.net?Subject=Re%3A%20%5Bpycrypto%5D%20RSA%20exportKey%28%29%20changes%20set%20in%20stone%20for%202.7%3F&In-Reply-To=%3CCAGwD-jYXxfVKyDyB6d%2BCV1uMSmo_v2C-j_FV%3D_qaHJ_rvjHqtQ%40mail.gmail.com%3E"
TITLE="[pycrypto] RSA exportKey() changes set in stone for 2.7?">kvogel at mdcom.com
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<I>Wed Jul 17 01:33:41 PDT 2013</I>
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<PRE>Hi, quick question for the group and maintainer...
I am about ready to deploy a project and wondering how set we are on the
format of rsa.exportKey() for next pycrypto?
Is it safe to include in our requirements.pip (for now) a reference to
<A HREF="https://github.com/dlitz/pycrypto">https://github.com/dlitz/pycrypto</A> master branch? And export my keys with
the new protection scheme? And consequently matching importKey().
It would be super nice if we could add **kwargs for iteration_count and
salt_size to export() but beggars can't be choosers :) It seems a simple
enough change and looks like importKey() reads those fields in, I'd do it
myself but would like any thoughts/opinions?
Thanks,
Kurt
On Mon, Jul 15, 2013 at 1:52 PM, Legrandin <<A HREF="http://lists.dlitz.net/cgi-bin/mailman/listinfo/pycrypto">helderijs at gmail.com</A>> wrote:
><i> Hi Kurt,
</I>><i>
</I>><i> I hope I understand correctly this time.
</I>><i> The presence of a header like:
</I>><i>
</I>><i> -----BEGIN RSA PRIVATE KEY-----
</I>><i> Proc-Type: 4,ENCRYPTED
</I>><i> DEK-Info: AES-256-CBC,16D792053CB9E5981B06E020900F86EA
</I>><i> [...]
</I>><i>
</I>><i> indicates that the PEM envelope is encrypted and that the inner PKCS#8
</I>><i> structure is clear.
</I>><i>
</I>><i> A header like:
</I>><i>
</I>><i> -----BEGIN ENCRYPTED PRIVATE KEY-----
</I>><i> MIIFHzBJBgkqhkiG9w0BBQ0wPDAbBgkqhkiG9w0BBQwwDgQIHI1C+JhO35cCAgPo
</I>><i> [...]
</I>><i>
</I>><i> indicates the opposite: the PEM envelope is clear and the inner PKCS#8
</I>><i> structure is encrypted. That was produced by a call like:
</I>><i>
</I>><i> >> rsa.exportKey(passphrase='boo', pkcs=8,
</I>><i> protection='PBKDF2WithHMAC-SHA1AndAES256-CBC')
</I>><i>
</I>><i> I don't think you can have both PKCS#8-level encryption (with all its
</I>><i> nice properties, like ability to fine tune the algorithms and so on)
</I>><i> and nice human-readable headers in the PEM envelope (like DEK-Info)
</I>><i> describing the type of encryption that was performed.That would
</I>><i> totally confuse the receiver...
</I>><i>
</I>><i> It' also worth streessing that PEM-level encryption is not really
</I>><i> specified anywhere other than in very old RFCs like RFC 1421, which
</I>><i> only define DES as algorithm and no password key derivation. Nowadays,
</I>><i> PEM-level encryption is best avoided, even if that means that the only
</I>><i> hint that the key is encrypted is the generic "BEGIN ENCRYPTED PRIVATE
</I>><i> KEY" line.
</I>><i>
</I>><i> As described in the docstrings, specifying the 'protection' parameter
</I>><i> automatically implies
</I>><i> PKCS#8-level encryption, so the change of export format is actually
</I>><i> done on purpose.
</I>><i>
</I>><i> > Also maybe more importantly would be the extra parameters for salt size
</I>><i> and
</I>><i> > iteration count?
</I>><i>
</I>><i> I agree it would be a nice addition (along with some support for
</I>><i> bcrypt/scrypt).
</I>><i>
</I>><i> > An afterthought, maybe it's time exportKey(), importKey() stay the same
</I>><i> as
</I>><i> > 2.6 and have new functions that allow these extra combinations?
</I>><i>
</I>><i> Which extra combinations? Salt size and iteration count you mean?
</I>><i> They could be passed as a dictionary, since they are
</I>><i> algorithm-specific parameters.
</I>><i>
</I>><i> 2013/7/15 Kurt Vogel <<A HREF="http://lists.dlitz.net/cgi-bin/mailman/listinfo/pycrypto">kvogel at mdcom.com</A>>:
</I>><i> >
</I>><i> > Understood, but the format of the export changes when we add 'protection'
</I>><i> > parameter.
</I>><i> > Can we keep same format and have different headers, ex:
</I>><i> >
</I>><i> >> Proc-Type: 4,ENCRYPTED
</I>><i> >> DEK-Info: AES-256-CBC,16D792053CB9E5981B06E020900F86EA
</I>><i> >
</I>><i> > Because I notice we wrap the unencrypted PEM into a PBES2 which is
</I>><i> encrypted
</I>><i> > there.
</I>><i> >
</I>><i> > Also maybe more importantly would be the extra parameters for salt size
</I>><i> and
</I>><i> > iteration count?
</I>><i> >
</I>><i> > An afterthought, maybe it's time exportKey(), importKey() stay the same
</I>><i> as
</I>><i> > 2.6 and have new functions that allow these extra combinations?
</I>><i> >
</I>><i> > Thanks,
</I>><i> > Kurt
</I>><i> >
</I>><i> >
</I>><i> >
</I>><i> > On Mon, Jul 15, 2013 at 2:26 AM, Legrandin <<A HREF="http://lists.dlitz.net/cgi-bin/mailman/listinfo/pycrypto">helderijs at gmail.com</A>> wrote:
</I>><i> >>
</I>><i> >> Hi Kurt,
</I>><i> >>
</I>><i> >> In the PyCrypto 2.6 release, rsa.exportKey(passphrase='boo') generates
</I>><i> >> a TDES-encrypted private key, with encryption being done at the PEM
</I>><i> >> level.
</I>><i> >>
</I>><i> >> I don't think that behavior should change (e.g. we should not silently
</I>><i> >> switch to AES or even to the more robust PKCS#8-level encryption).
</I>><i> >>
</I>><i> >> 2013/7/15 Kurt Vogel <<A HREF="http://lists.dlitz.net/cgi-bin/mailman/listinfo/pycrypto">kvogel at mdcom.com</A>>:
</I>><i> >> > And finally a comment/question/complaint :(
</I>><i> >> >
</I>><i> >> > If I use protection like this for ex:
</I>><i> >> >
</I>><i> >> > export = rsa.exportKey(passphrase='boo', pkcs=8,
</I>><i> >> > protection='PBKDF2WithHMAC-SHA1AndAES256-CBC')
</I>><i> >> >
</I>><i> >> > The exported key looks like this:
</I>><i> >> >
</I>><i> >> > -----BEGIN ENCRYPTED PRIVATE KEY-----
</I>><i> >> > MIIFHzBJBgkqhkiG9w0BBQ0wPDAbBgkqhkiG9w0BBQwwDgQIHI1C+JhO35cCAgPo
</I>><i> >> > MB0GCWCGSAFlAwQBKgQQ2FsezYUEaQLPHxk0z6+R4gSCBNDV++BsvKxxpo6uhUYw
</I>><i> >> > ...
</I>><i> >> >
</I>><i> >> > With export = rsa.exportKey(passphrase='boo'):
</I>><i> >> >
</I>><i> >> > -----BEGIN RSA PRIVATE KEY-----
</I>><i> >> > Proc-Type: 4,ENCRYPTED
</I>><i> >> > DEK-Info: DES-EDE3-CBC,CE7B6EC598ED0D10
</I>><i> >> >
</I>><i> >> > lPMvbYUypG+O4P/LilzGVQqP+6PMbnnLMP6eosyubcBqLtQxvMlvRRqgRu5CDApA
</I>><i> >> > ...
</I>><i> >> >
</I>><i> >> > The logic in exportKey() looks a bit convoluted, is this for some
</I>><i> >> > backward
</I>><i> >> > compatibility issue? I would expect to see something like this, what
</I>><i> >> > ssh-key does:
</I>><i> >> >
</I>><i> >> > -----BEGIN RSA PRIVATE KEY-----
</I>><i> >> > Proc-Type: 4,ENCRYPTED
</I>><i> >> > DEK-Info: AES-256-CBC,16D792053CB9E5981B06E020900F86EA
</I>><i> >> >
</I>><i> >> > oL8O6n5v1S3cgGJIwrzrAq5TQIb7OeolGJpHXiyTUj1iStulgS5vAjkht0cgq53p
</I>><i> >> > ...
</I>><i> >> > ..
</I>><i> >> >
</I>><i> >> > Thanks,
</I>><i> >> > Kurt
</I>><i> >> >
</I>><i> >> >
</I>><i> >> > On Sun, Jul 14, 2013 at 11:40 PM, Kurt Vogel <<A HREF="http://lists.dlitz.net/cgi-bin/mailman/listinfo/pycrypto">kvogel at mdcom.com</A>>
</I>><i> wrote:
</I>><i> >> >>
</I>><i> >> >> While I'm on the subject and appears Dwayne is merging in pull
</I>><i> requests
</I>><i> >> >> :)
</I>><i> >> >>
</I>><i> >> >> For RSA exportKey() think we could have **kwargs for extra
</I>><i> prot_params
</I>><i> >> >> passed to
</I>><i> >> >>
</I>><i> >> >> PKCS8.wrap() like iteration_count and salt size?
</I>><i> >> >>
</I>><i> >> >>
</I>><i> >> >>
</I>><i> >> >> On Sun, Jul 14, 2013 at 9:34 PM, Kurt Vogel <<A HREF="http://lists.dlitz.net/cgi-bin/mailman/listinfo/pycrypto">kvogel at mdcom.com</A>>
</I>><i> wrote:
</I>><i> >> >>>
</I>><i> >> >>> Hi,
</I>><i> >> >>>
</I>><i> >> >>> Do you guys know roughly when this will go in?
</I>><i> >> >>>
</I>><i> >> >>> Also with import/export RSA keys can we support bcrypt?
</I>><i> >> >>>
</I>><i> >> >>> Does JCA and BouncyCastle use bcrypt, eg:
</I>><i> >> >>>
</I>><i> >> >>> 'BcryptWithHMAC-SHA1AndAES256-CBC'
</I>><i> >> >>>
</I>><i> >> >>> Thanks,
</I>><i> >> >>> Kurt
</I>><i> >> >>>
</I>><i> >> >>>
</I>><i> >> >>> On Fri, Jul 5, 2013 at 2:52 AM, Legrandin <<A HREF="http://lists.dlitz.net/cgi-bin/mailman/listinfo/pycrypto">helderijs at gmail.com</A>>
</I>><i> wrote:
</I>><i> >> >>> >
</I>><i> >> >>> > Hi Kurt , thanks a lot for providing feedback. It is much
</I>><i> >> >>> > appreciated.
</I>><i> >> >>> >
</I>><i> >> >>> > * I guess you refer to camel-casing used for several variables,
</I>><i> >> >>> > which
</I>><i> >> >>> > was due to my preference to stick to ASN.1 naming.
</I>><i> >> >>> > I can work on that and make sure flake8 does not complain that
</I>><i> >> >>> > much.
</I>><i> >> >>> >
</I>><i> >> >>> > * Right. Code evolved at different points in time, and indeed it
</I>><i> is
</I>><i> >> >>> > now hard to follow the path of the 'parameter' value. I will try
</I>><i> to
</I>><i> >> >>> > fix that.
</I>><i> >> >>> >
</I>><i> >> >>> > * I used strings like 'PBKDF2WithHMAC-SHA1AndAES128-CBC' because
</I>><i> >> >>> > that
</I>><i> >> >>> > is the style used in JCA and BouncyCastle and a lot of people are
</I>><i> >> >>> > familiar with it.
</I>><i> >> >>> > I am not very clear what the benefit enums might bring? One
</I>><i> option
</I>><i> >> >>> > I
</I>><i> >> >>> > considered was the ability to provide 3 independent parameters
</I>><i> >> >>> > instead of one (since protection mainly depends on type of KDF,
</I>><i> >> >>> > PRF,
</I>><i> >> >>> > and symmetric cipher) but at the end I guess most
</I>><i> >> >>> > uses case are about the desire to protect the private key using
</I>><i> a
</I>><i> >> >>> > password in a strong way, and the ability to tweak the various
</I>><i> >> >>> > parameters
</I>><i> >> >>> > is not that relevant. Plus, exportKey() parameter list becomes
</I>><i> to
</I>><i> >> >>> > long.
</I>><i> >> >>> >
</I>><i> >> >>> > * I am really ashamed to admit that I actually have 9 pull
</I>><i> requests
</I>><i> >> >>> > open, not 2 so I am totally giving headaches to the maintainer.
</I>><i> :-)
</I>><i> >> >>> > It is of course only up to him to decide which features should
</I>><i> go
</I>><i> >> >>> > in; given that he has not much time these days, it is likely that
</I>><i> >> >>> > only
</I>><i> >> >>> > few features and bugfixes may go into any next release.
</I>><i> >> >>> > The release merge window seems to roughly be once per year and I
</I>><i> >> >>> > find it is natural to have so many outstanding pull requests by
</I>><i> now.
</I>><i> >> >>> > To my defense, I can only say that the all pull requests cover
</I>><i> one
</I>><i> >> >>> > feature only and that I try to keep them as independent as
</I>><i> possible.
</I>><i> >> >>> > Most of them apply cleanly to master (e.g. HKDF, CCM, PKCS#8,
</I>><i> bug
</I>><i> >> >>> > fixes, etc).
</I>><i> >> >>> > In some cases though, they do depend on an existing pull request
</I>><i> >> >>> > (as
</I>><i> >> >>> > in the case of DSA import/export depending on PKCS8 be applied
</I>><i> >> >>> > first),
</I>><i> >> >>> > because keeping them separated is honestly too much work for me
</I>><i> >> >>> > *and* they are indeed extensions of other extensions.
</I>><i> >> >>> >
</I>><i> >> >>> > > Hi, I was looking at the pycrypto pull request
</I>><i> >> >>> > > <A HREF="https://github.com/dlitz/pycrypto/pull/32.">https://github.com/dlitz/pycrypto/pull/32.</A> Just a few
</I>><i> comments...
</I>><i> >> >>> > >
</I>><i> >> >>> > > * For readability can you pep8 format the code?
</I>><i> >> >>> > > * RSA, for import/export the protection parameter maybe rename
</I>><i> to
</I>><i> >> >>> > > algo or
</I>><i> >> >>> > > wrap algo? It evolves from: 'protection' to 'wrap_algo' to
</I>><i> 'mode'
</I>><i> >> >>> > > as
</I>><i> >> >>> > > it
</I>><i> >> >>> > > goes down the call stack.
</I>><i> >> >>> > > * Also maybe make this parameter an enum/value? Since the long
</I>><i> >> >>> > > string can
</I>><i> >> >>> > > be error prone, low level code would need to change anyway if it
</I>><i> >> >>> > > were
</I>><i> >> >>> > > either
</I>><i> >> >>> > > string or int if we support more modes.
</I>><i> >> >>> > > * And last but not least... I'm new to this email list and not
</I>><i> >> >>> > > sure
</I>><i> >> >>> > > how
</I>><i> >> >>> > > often pull requests are accepted but maybe you could reduce the
</I>><i> >> >>> > > amount of
</I>><i> >> >>> > > features going in? I know you have another one, 51, after
</I>><i> this...
</I>><i> >> >>> > > Maintainer may reluctant to do massive changes all at once?
</I>><i> >> >>> > >
</I>><i> >> >>> > > Anyway just ideas...
</I>><i> >> >>> > > Thanks for your time,
</I>><i> >> >>> > > Sincerely,
</I>><i> >> >>> > > Kurt
</I>><i> >> >>> > >
</I>><i> >> >>> > _______________________________________________
</I>><i> >> >>> > pycrypto mailing list
</I>><i> >> >>> > <A HREF="http://lists.dlitz.net/cgi-bin/mailman/listinfo/pycrypto">pycrypto at lists.dlitz.net</A>
</I>><i> >> >>> > <A HREF="http://lists.dlitz.net/cgi-bin/mailman/listinfo/pycrypto">http://lists.dlitz.net/cgi-bin/mailman/listinfo/pycrypto</A>
</I>><i> >> >>>
</I>><i> >> >>
</I>><i> >> >
</I>><i> >> >
</I>><i> >> > _______________________________________________
</I>><i> >> > pycrypto mailing list
</I>><i> >> > <A HREF="http://lists.dlitz.net/cgi-bin/mailman/listinfo/pycrypto">pycrypto at lists.dlitz.net</A>
</I>><i> >> > <A HREF="http://lists.dlitz.net/cgi-bin/mailman/listinfo/pycrypto">http://lists.dlitz.net/cgi-bin/mailman/listinfo/pycrypto</A>
</I>><i> >> >
</I>><i> >> _______________________________________________
</I>><i> >> pycrypto mailing list
</I>><i> >> <A HREF="http://lists.dlitz.net/cgi-bin/mailman/listinfo/pycrypto">pycrypto at lists.dlitz.net</A>
</I>><i> >> <A HREF="http://lists.dlitz.net/cgi-bin/mailman/listinfo/pycrypto">http://lists.dlitz.net/cgi-bin/mailman/listinfo/pycrypto</A>
</I>><i> >
</I>><i> >
</I>><i> >
</I>><i> > _______________________________________________
</I>><i> > pycrypto mailing list
</I>><i> > <A HREF="http://lists.dlitz.net/cgi-bin/mailman/listinfo/pycrypto">pycrypto at lists.dlitz.net</A>
</I>><i> > <A HREF="http://lists.dlitz.net/cgi-bin/mailman/listinfo/pycrypto">http://lists.dlitz.net/cgi-bin/mailman/listinfo/pycrypto</A>
</I>><i> >
</I>><i> _______________________________________________
</I>><i> pycrypto mailing list
</I>><i> <A HREF="http://lists.dlitz.net/cgi-bin/mailman/listinfo/pycrypto">pycrypto at lists.dlitz.net</A>
</I>><i> <A HREF="http://lists.dlitz.net/cgi-bin/mailman/listinfo/pycrypto">http://lists.dlitz.net/cgi-bin/mailman/listinfo/pycrypto</A>
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