WG Chair hat = OFF
On 22/07/2009, at 6:25 AM, Stephen Kent wrote:
Geoff, Roque & David,
I do not disagree with David's technical observation about the
crypto strength matching of SHA-1 and RSA 1024 However, this
observation does not mean that we have to use SHA-1 with RSA 1024,
from an architectural perspective.
We specified use of SHA-256 (as a minimum), because we want to use
that hash algorithm with larger (2048) RSA key sizes, and we wanted
to encourage support for the SHA-2 family of hash algorithms as part
of a longer term transition strategy. As the most recent version of
the CP notes, we anticipate that CAs will transition to longer keys
and/or different algorithms over time, as required to maintain
appropriate crypto security for signatures in the RPKI. I think it
is reasonable to mandate support for SHA-256 now, to get people in
the habit of using that family of hash algorithms now, as it is
likely that we will migrate to these algorithms over time.
Thus I suggest that we stick with the current hash algorithm
requirements, irrespective of key sizes. If the WG decides that we
should up the minimum key size from 1,204 bits, that's fine too, but
we need not maintain crypto security equivalence between the two
parameters based on David's observation. There can be other reasons
for selecting parameters in contexts like these.
I am unclear what "stick with current algorithm requirements" means in
this context.
The "current" text in the WG document, is the text that matches
David's review comment in early September, namely:
-----
3.8. Subject Public Key Info
This field specifies the subject's public key and the algorithm with
which the key is used. The public key algorithm MUST be RSA, and,
accordingly, the OID for the public key algorithm is
1.2.840.113549.1.1.1. The key size MUST be a minimum size of 2048 bits.
It is noted that larger key sizes are computationally expensive for
both the CA and relying parties, indicating that care should be taken
when deciding to use larger than the minimum key size noted above.
-----
My interpretation of your suggestion to stick with current hash
algorithm requirements is that you are proposing to stick with the
current text in this draft.
thanks,
Geoiff
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