Re: des-die-die-die and RC4

Tom Yu wrote:
> 
> Martin Rex <[email protected]> writes:
> 
> > I'm fine with deprecating 1DES and RC4-40/RC4-56,
> > and believe the RC4-128 based enctype will still be needed for interop
> > for a couple of years.
> 
> I am not recalling Microsoft releasing any RC4 variant that has a
> 40-bit key size, and RFC 4757 seems to specify a 56-bit variant, not a
> 40-bit variant.

I'm sorry, you're right.

I was confused by this statement:

          OCTET L40[14] = "fortybits";

but the actual truncation of the RC4 key is this:

          if (export) memset (K1+7, 0xAB, 9);

which flattens 9 of 16 octets (and therefore leave 7 octets = 56 bits).



> 
> > Actually, I would prefer the document to use a different quoting:
> >
> >    "export strength RC4"  or "40-bit RC4 (RC4_EXP)"
> >
> > rather than
> >
> >    "export strength" RC4
> 
> What semantic difference would you want to imply by making such a
> change?  (I assume you mean changing the quoting in both the title and
> the body.)
> 

The latter could be interpreted that RC4 is "export strength",
although the term "export strength" is not an attribute to RC4 in
general, but to variants of RC4 with a purposely short (or truncated) key.

Not everyone is aware what "export strength" means.
With respect to RC4 export strength was originally 40(!) bit.


-Martin




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