Re: [Trans] [trans] #79 (rfc6962-bis): Precertificate signaturemust be over something other than just the TBSCertificate

[Rob Stradling <[e-mail]>]

On 11/06/15 22:42, Stephen Kent wrote:
> what does it mean to not be "an X509 signature"?
>
> I thought the intent was to use a CMS object, and thus the signature
> would be defined by that (profiled) CMS object.

Hi Steve.  That's correct.

At the top of ticket #79 I wrote:
"If I understand the CMS spec correctly, then we're currently defining a 
Precertificate to be a CMS structure that contains a TBSCertificate and 
a signature over just that TBSCertificate.
That means that the components of a Precertificate can be trivially 
rearranged into an X.509 certificate with a valid signature!"

It turns out that I didn't understand correctly.  :-)

Ben added some text to help clarify the situation:
"Note that, because of the structure of CMS, the signature on the CMS 
object will not be a valid X.509v3 signature and so cannot be used to 
construct a certificate from the precertificate."

>> #79: Precertificate signature must be over something other than just the
>> TBSCertificate
>>
>> Changes (by [e-mail]):
>>
>>   * milestone:   => review
>>
>>
>> Comment:
>>
>>   After discussion with Rob, core point is that the CMS signature is
>> not an X509 signature.
>>
>>   Fixed at https://github.com/google/certificate-transparency-
>>   rfcs/commit/546e6e9451186e96ddd7b54ca02f17c8d86f951e.

-- 
Rob Stradling
Senior Research & Development Scientist
COMODO - Creating Trust Online