Re: Best practices: time-stamps comments

It is very useful to maintain this distinction, thank you for  
pointing this out Pratik.  The WSS usage is what appeared to me in  
the original reading.

regards, Frederick

Frederick Hirsch
Nokia



On Jun 10, 2008, at 2:40 AM, ext Pratik Datta wrote:

> The word "timestamp"  means two different things in WSS and XAdES
>
> In WSS, the timestamp is just a dateTime value. It represents the  
> time, the signature was created, or the time the signature expires.
> But in XAdes and DSS timestamp is actually a signature which signs  
> a dateTime Value and message Digest.
>
> To avoid confusion we need to use a different name for these two  
> concepts. I changed the document to use "dateTime" or "Signing  
> time" for the WSS meaning of timestamp. I also added a separate  
> section for XAdES.
>
> http://www.w3.org/2007/xmlsec/Drafts/xmldsig-bestpractices/
>
> Pratik
>
> Juan Carlos Cruellas wrote:
>>
>> Frederick Hirsch escribió:
>>> Is it correct to say that some timestamps might not always be  
>>> intended for long term signatures, and thus not need to meet the  
>>> XAdES approach in those short term cases?
>>>
>> Yes....
>>> Why cannot a timestamp and nonce be generated, and  then the  
>>> signature including references to those items? You suggest the  
>>> signature must be generated first?
>>>
>> I am not saying that, what I am saying is that as I read the text  
>> before it did not clarify what was time-stamped by the time-stamp  
>> generated before signing, and obviously, if this is the case, what  
>> it may not be time-stamped is the signature.
>>
>> There are a number of things that we may do:
>>
>> Step 1: generate a nonce, time-stamp (TST-N) the nonce and/or  
>> other to be signed data objects. TST-N would prove when the nonce  
>> was generated and/or the to be signed data existed
>>
>> Step 2: sign the data objects, the nonce and TST-N.
>>
>> Step 3: time-stamp the signature (TST-S). This TST-S would prove  
>> when the signature was created.
>>
>> The text dealing with nonce and time-stamp should clarify what  
>> time-stamp is talking about, the TST-N or the TST-S, as each is  
>> for a different purpose. In addition to that, XAdES  specifies  
>> elements able to encapsulate both TSTs.
>>
>>
>> Juan Carlos.
>>> regards, Frederick
>>>
>>> Frederick Hirsch
>>> Nokia
>>>
>>>
>>>
>>> On May 20, 2008, at 8:04 AM, ext Juan Carlos Cruellas wrote:
>>>
>>>>
>>>> Dear all,
>>>>
>>>> Some comments on time-stamps best practices.
>>>>
>>>> 1. I suggest to substitute the text: "DSS Profiles contain  
>>>> timestamps" by some text that provide some hints on XAdES way of  
>>>> using time-stamping for long term signatures and how DSS  
>>>> profiles deal with the request and verification of such issues.
>>>>
>>>> Proposed text:
>>>>
>>>> "ETSI has produced TS 101 903: "XML Advanced Electronic  
>>>> Signatures (XAdES)", which among other ones, deals with the  
>>>> issue of long-term electronic signatures. It has defined a  
>>>> standard way for incorporating time-stamps to XML signatures. In  
>>>> addition to the signature time-stamp, which should be generated  
>>>> soon after the generation of the signature, other time-stamps  
>>>> may be added to the signature structure protecting the  
>>>> validation material used by the verifier. Recurrent time- 
>>>> stamping (with stronger algorithms and keys) on all these items,  
>>>> i.e., the signature, the validation material and previous time- 
>>>> stamps counters the revocation of validation data and weaknesses  
>>>> of cryptographic algorithms and keys.
>>>>
>>>> OASIS DSS core specifies a XML format for time-stamps based in  
>>>> XML Sig. In addition DSS core and profiles allow the generation  
>>>> and verification of signatures, time-stamps, and time-stamped  
>>>> signatures by a centralized server"
>>>>
>>>> 2. Best practice 14.
>>>> This reads: "Nonce and timestamp must be signature protected."
>>>>
>>>> Is this correct? I have the impression taht in this section we  
>>>> are speaking of time-stamps of signatures, ie, time-stamps  
>>>> generated after the signature has been produced so that we may  
>>>> prove that at certain point of time the signature already  
>>>> existed; how the time-stamp could be protected by this  
>>>> signature? In addition, a time-stamp  is a secure piece of  
>>>> information: by the TSA's signature (RFC3161 or the DSS time- 
>>>> stamp) or because of the linking mechanism.
>>>>
>>>> Reading what comes before this text:
>>>>
>>>> "Nonces and passwords must fall under at least one signature to  
>>>> be effective. In addition, the signature should include at least  
>>>> a critical portion of the message payload, otherwise an attacker  
>>>> might be able to discard the timestamp and its signature without  
>>>> arousing suspicion.
>>>>
>>>>
>>>> I have the impression that the  Best practice 14 text should be:
>>>> "Nonce and passwords must be signature protected."
>>>>
>>>>
>>>> Regards
>>>>
>>>> Juan Carlos.
>>>> Best Practice 14:
>>>>
>>>>
>>>>
>>
>>
>

Received on Tuesday, 10 June 2008 12:50:36 UTC