Re: [GNU Crypto] how to deal with weak keys. was: Documentation

[Raif S. Naffah]

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hello Simon,

On Wed, 28 May 2003 09:31 pm, Simon Josefsson wrote:
> "Raif S. Naffah" <address@hidden> writes:
> >> My vote is to not check for weak keys. Any user-level applications
> >> we eventually write for GNU Crypto most definitely *should* check
> >> for weak keys when they are generated, but I don't think this
> >> belongs in the library proper.
> >
> > i hear you.
>
> My vote is to implement it, but make the check optional somehow. 
> Weak key testing is useful to have in the library, and some
> applications really do need it (cf kerberos des string2key).  Those
> who do not need doesn't have to use it.
>
> > ok.  i see the benefit of allowing even weak keys to go through the
> > implementation.  i double checked all the FIPS publications
> > relevant to DES, and couldnt find even a warning about weak keys!
>
> See FIPS 74 section 3.6.  It mentions the weak and semi-weak keys,
> but not the pseudo-weak keys (using Schneier's terminology).
>
> http://www.itl.nist.gov/fipspubs/fip74.htm

got it.  thanks.


> > * add in each cipher implementation which is known to exhibit weak,
> > or semi-weak keys, a private static final boolean CHECK_WEAK_KEYS
> > with a default value.  in the makeKey() method we add the code to
> > check for weak keys conditioned by the value of CHECK_WEAK_KEYS.
> >
> > * in the code, distinguish the case of weak keys with a new
> > exception that is a subclass of InvalidKeyException.  this way the
> > code will remain backward compatible.
> >
> > * add a warning in the documentation, incl. the README about the
> > set default for CHECK_WEAK_KEYS, and how the user can change it to
> > get the desired effect if it is not set to the appropriate value.
> >
> >
> > how does this sound?
>
> Sounds good to me.


- -- 
cheers;
rsn
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