RE: Key Sizes in S/MIME v3.2

The point is that we should be able to validate a signature that was 
generated by a key pair that was generated under the previous recommendations.
Russ


At 12:10 PM 2/20/2008, Turner, Sean P. wrote:

> As I dig around, I find that 1024 is pretty much the minimum that is
> recommended. Both NIST (SP 800-78) and RSA
> (http://www.rsa.com/rsalabs/node.asp?id=2004) recommend at least 1024 now.
> Also, I'm not sure I've ever actually seen a 768-bit key in a certificate -
> all I've seen for years now is 1024.
>
> spt
>
> >-----Original Message-----
> >From: owner-ietf-smime(_at_)mail(_dot_)imc(_dot_)org
> >[mailto:owner-ietf-smime(_at_)mail(_dot_)imc(_dot_)org] On Behalf Of Denis 
> Pinkas
> >Sent: Wednesday, February 20, 2008 11:34 AM
> >To: ietf-smime(_at_)imc(_dot_)org
> >Subject: Re: Key Sizes in S/MIME v3.2
> >
> >
> >
> >
> >>How about for 3851bis: A user agent SHOULD generate RSA key
> >pairs at a
> >>minimum key size of 1024 bits.  A user agent MUST NOT
> >generate RSA key
> >>pairs less than 1024 bits long.
> >
> >With these two sentences there is no more room for key sizes
> >less than 1024 bits.
> >768 bits is still fully adequate, even we can recommend to use
> >1024 bits as the minimum.
> >
> >Denis
> >
> >>I'll move the 768 back to 512 as suggested by Simon.
> >>
> >>spt
> >>>-----Original Message-----
> >>>From: Russ Housley [mailto:housley(_at_)vigilsec(_dot_)com]
> >>>Sent: Wednesday, February 20, 2008 9:16 AM
> >>>To: Turner, Sean P.
> >>>Cc: ietf-smime(_at_)imc(_dot_)org
> >>>Subject: RE: Key Sizes in S/MIME v3.2
> >>>
> >>>Sean:
> >>>
> >>>Given the proposed text, it sounds like you really want to say that
> >>>key sizes from 768 to 2048 bits must be supported, even
> >though you are
> >>>recommending 1024 bits as the minimum for newly generated keys.
> >>>
> >>>Russ
> >>>
> >>>At 07:17 AM 2/20/2008, Turner, Sean P. wrote:
> >>>
> >>>>I should have been clearer.
> >>>>
> >>>>RFC 3850 current says (sec 4.3):
> >>>>
> >>>>  Key sizes from 512 bits to 2048 bits MUST be supported.
> >>>>
> >>>>Suggesting it be replaced with:
> >>>>
> >>>>  Key sizes from 1024 bits to 2048 bits MUST be supported.
> >>>>
> >>>>Here are the suggested changes RFC 3851 (sec 4.1):
> >>>>
> >>>>  If an S/MIME agent needs to generate an RSA key pair,  then the
> >>>> S/MIME agent or some related administrative  utility or function
> >>>> SHOULD generate RSA key pairs  using the following
> >>>guidelines.  A user
> >>>> agent SHOULD  generate RSA key pairs at a minimum key size of 1024
> >>>>                                          was 768 ^^^^
> >bits.  A user
> >>>> agent MUST NOT generate RSA key pairs  less than 768 bits long.
> >>>> Creating keys longer than
> >>>>            ^^^ was 512
> >>>>  1024 bits can cause some older S/MIME receiving agents  to not be
> >>>> able to verify signatures, but gives better  security and is
> >>>therefore
> >>>> valuable.  A receiving agent  SHOULD be able to verify
> >>>signatures with
> >>>> keys of any  size over 768 bits. Some agents created in the United
> >>>>            ^^^ was 512
> >>>>  States have chosen to create 512 bit keys in order to  get more
> >>>> advantageous export licenses.  However, 512  bit keys are
> >considered
> >>>> by many to be cryptographically  insecure. Implementers SHOULD be
> >>>> aware that multiple
> >>>>  (active) key pairs can be associated with a single
> >>>individual.  For
> >>>> example, one key pair can be used  to support
> >>>confidentiality, while a
> >>>> different key pair  can be used for authentication.
> >>>>
> >>>>Thoughts?
> >>>>
> >>>>spt
> >>>>
> >>>> >-----Original Message-----
> >>>> >From: owner-ietf-smime(_at_)mail(_dot_)imc(_dot_)org
> >>>> >[mailto:owner-ietf-smime(_at_)mail(_dot_)imc(_dot_)org] On Behalf Of Paul 
> Hoffman
> >>>> >Sent: Tuesday, February 19, 2008 1:42 PM
> >>>> >To: Turner, Sean P.; ietf-smime(_at_)imc(_dot_)org
> >>>> >Subject: Re: Key Sizes in S/MIME v3.2
> >>>> >
> >>>> >
> >>>> >At 11:34 AM -0500 2/19/08, Turner, Sean P. wrote:
> >>>> >>  >From the mail discussion we had in December, it's pretty
> >>>> >clear to me
> >>>> >>that key sizes from 1024-2048 ought to be the MUST and other
> >>>> >key sizes are MAY.
> >>>> >>I'm suggesting the following text:
> >>>> >>
> >>>> >>Key sizes from 1024 bits to 2048 buts MUST be supported.
> >>>Keys sizes
> >>>> >>larger than 2048 MAY be supported.
> >>>> >
> >>>> >Sure.
> >>>> >
> >>>> >>Should we put a MUST NOT or SHOULD NOT in for key sizes
> >>>> >smaller than 1024?
> >>>> >
> >>>> >MUST NOT or SHOULD NOT *what*? Generate, or validate?
> >>>> >
> >>>
> >>
> >>
> >
> >Regards,
> >
> >Denis Pinkas
> >
> >
> >