Re: [lamps] Double signatures

[Massimiliano Pala <[e-mail]>]

Hi Russ, all,

my personal position is that the signer MUST use all the keys that have
digitalSignature set, the verifier shall verify all the signatures for
which it does have support for.

The rationale for this is that if I certify a public key in the
certificate, you should be able to use the private key to generate the
signature, therefore the approach is the same as usual: sign with your
key. In this case, it just happens that to generate the signature you
have to generate multiple ones and then combine them together.

For the application that verifies those signatures, it is always a
question of what is the threshold that is acceptable for the application
(in terms of risk) in case it does not support all of the algorithms
that are used to generate the composite signature. Ideally it would
verify all, but it may decide to verify less (at least one).

I also saw the other e-mail from Jim on this topic and I think it could
be a good idea - the use of the two OIDs is another way to go to codify
the validation process required. Technically, that makes sense to me,
however I am conflicted as this approach requires that the signer has an
understanding of what the verifier's capabilities are... I think that
defining two OIDs for the signatures could still be useful because the
signer might then decide the "recommended"/"intended" verification
behavior... I can see some use-cases that might have a composite key
with { RSA, EC } and the "Must-Verify-All" OID for the signature, and
another use-case where we have a composite key with { RSA, HASH-BASED }
and for the signature "Must-Verify-At-Least-One".

Does this make sense?

Cheers,
Max


On 9/12/18 6:12 AM, Russ Housley wrote:
> Max:
>
> During a transition to quantum-resistant signatures, a signer wants to
> put a traditional signature and a quantum-resistant signature on an
> object.  Given your description of keyUsage and extendedKeyUsage, both
> would have the digitalSignature bit set.  How does a client know if
> just one or both signatures must be valid?
>
> As Jim Schaad already said, RFC 5752 talks about this issue when a CMS
> SignedData contains more than one SignerInfo.
>
> Russ
>
>
>> On Sep 11, 2018, at 4:45 PM, Max Pala <[e-mail]
>> <mailto:[e-mail]>> wrote:
>>
>> Hi All,
>>
>> I am working on a similar - but different - solution, in particular I
>> solve the issue of (a) being able to combine more than one public
>> key, (b) only one (actually two) OIDs required, and (c) simply the
>> processing by re-utilizing the same data structures we have today.
>>
>> I particular, I define a “composite public key” and “composite
>> signature”.
>>
>> The first one encodes in the key value’s BITSTRING the DER value of
>> the SEQUENCE of public keys (each of which is a the
>> subjectPublicKeyInfo structure) and uses a specific OID that
>> identifies the public key type. The parameters of the compositeKey
>> algorithm can be used to encode the keyUsage and the extendedKeyUsage
>> for each of the keys in the composite key.
>>
>> The same approach is used for the “Composite Signature” case where
>> the value of the signature is the DER representation of the SEQUENCE
>> of signatures made with each of the keys.
>>
>> As soon as I have some spare time, I will submit the draft - maybe
>> this could be discussed in Bangkok?
>>
>> This simple idea allows us to have all the other procedures related
>> to PKIs work - this means we can combine ECC with RSA or with a
>> Quantum-Resistant algorithm (when finally available and
>> standardized). A step forward for the deployment of hybrid-PKIs where
>> multiple Lagos for keys can be used to authenticate data, certs,
>> revocation data, etc... we plan to use this in our infrastructures to
>> provide a transitional path for post-Quantum transition and to
>> further improve the algorithm-agility capability of PKIs.
>>
>> What do you think?
>>
>> Cheers,
>> Max
>>
>>
>>
>>
>> ---
>>
>> Cheers,
>> Max
>> On Sep 11, 2018, at 8:38 AM, Tim Hollebeek
>> <[e-mail] <mailto:[e-mail]>> wrote:
>>
>>> Unfortunately, “not every combination needs to be covered”
>>> introduces a lot of politics around choosing which combinations
>>> “need to be covered”, a subject on which inevitably not everyone
>>> agrees.  I would rather avoid all those discussions and the
>>> unnecessary work they represent.
>>>  
>>> I personally don’t think a single AlgID which implies a SEQUENCE of
>>> ALG IDs is an improvement over a SEQUENCE of ALG IDs, or its moral
>>> equivalent.  For simple hybrid use cases, there is also a lot of
>>> value in having the classical algorithm ID being the same as it
>>> usually is, to allow easier interoperability with older systems that
>>> don’t understand the newer algorithms (and can blissfully ignore them).
>>>  
>>> -Tim
>>>  
>>> *From:* Santosh Chokhani <[e-mail]
>>> <mailto:[e-mail]>> 
>>> *Sent:* Tuesday, September 11, 2018 10:29 AM
>>> *To:* Tim Hollebeek <[e-mail]
>>> <mailto:[e-mail]>>; 'Erik Andersen' <[e-mail]
>>> <mailto:[e-mail]>>; 'SPASM' <[e-mail]
>>> <mailto:[e-mail]>>; [e-mail]
>>> <mailto:[e-mail]>
>>> *Subject:* RE: [lamps] Double signatures
>>>  
>>> Thanks Tim.
>>>  
>>> There are ways to accommodate your concern.
>>>  
>>> One way to handle this is defining a single Alg ID A which implies a
>>> SEQUENCE of ALG IDs and define the relying party rules in terms of
>>> its ability to process one or all ALG IDs.
>>>  
>>> Another way to do this is not every combination needs to be covered
>>> and the user community defines its own  Alg ID Xi which maps to a
>>> SEQUENCE of ALG IDs.
>>>  
>>> *From:* Spasm [mailto:[e-mail]] *On Behalf Of *Tim
>>> Hollebeek
>>> *Sent:* Tuesday, September 11, 2018 10:03 AM
>>> *To:* Erik Andersen <[e-mail] <mailto:[e-mail]>>; 'SPASM'
>>> <[e-mail] <mailto:[e-mail]>>; [e-mail]
>>> <mailto:[e-mail]>
>>> *Subject:* Re: [lamps] Double signatures
>>>  
>>> Doesn’t the combinatoric explosion render this completely impractical?
>>>  
>>> You need N_c x N_pq algorithm identifiers just to handle the simple
>>> hybrid use case where a single classical algorithm is being used in
>>> conjunction with a single post-quantum algorithm.
>>>  
>>> And there are people who want to use multiple post-quantum
>>> algorithms to hedge against potential yet to be discovered
>>> weaknesses in post-quantum algorithms.
>>>  
>>> I’m not really looking forward to trying to allocate or manage O(N_c
>>> x N_pq^3) algorithm identifiers…
>>>  
>>> -Tim
>>>  
>>> *From:* Spasm <[e-mail]
>>> <mailto:[e-mail]>> *On Behalf Of *Erik Andersen
>>> *Sent:* Tuesday, September 11, 2018 3:10 AM
>>> *To:* 'SPASM' <[e-mail]
>>> <mailto:[e-mail]>>; [e-mail]
>>> <mailto:[e-mail]>
>>> *Subject:* Re: [lamps] Double signatures
>>>  
>>> Hi Santosh,
>>>  
>>> You have proposed something like this before. It still puzzling in
>>> my brain. As I understand, it requires that we define a particular
>>> algorithm that has a parameter that includes the things you suggest.
>>> It is worthy to be analysed.
>>>  
>>> Erik
>>>  
>>> *Fra:* Spasm [mailto:[e-mail]] *På vegne af *Santosh
>>> Chokhani
>>> *Sendt:* 10 September 2018 19:18
>>> *Til:* 'Jim Schaad' <[e-mail]
>>> <mailto:[e-mail]>>; 'Ryan Sleevi'
>>> <[e-mail] <mailto:[e-mail]>>; [e-mail]
>>> <mailto:[e-mail]>
>>> *Cc:* 'SPASM' <[e-mail]
>>> <mailto:[e-mail]>>; [e-mail]
>>> <mailto:[e-mail]>
>>> *Emne:* Re: [lamps] Double signatures
>>>  
>>> Why not let algorithm identifier dictate the number of signatures
>>> and their syntax?
>>>  
>>> *From:* Spasm [mailto:[e-mail]] *On Behalf Of *Jim Schaad
>>> *Sent:* Monday, September 10, 2018 1:07 PM
>>> *To:* 'Ryan Sleevi' <[e-mail]
>>> <mailto:[e-mail]>>; [e-mail] <mailto:[e-mail]>
>>> *Cc:* 'SPASM' <[e-mail]
>>> <mailto:[e-mail]>>; [e-mail]
>>> <mailto:[e-mail]>
>>> *Subject:* Re: [lamps] Double signatures
>>>  
>>> Ryan,
>>>  
>>> The discussion in London dealt with a completely different proposal
>>> than this one.  While I think there are problems with this that need
>>> to be dealt with they are mostly not the same set.
>>>  
>>> Erik,
>>>  
>>> Why is this considered to be a preferred solution to defining a new
>>> signature algorithm which contains as the parameter the sequence of
>>> algorithm identifiers and as the signature value a sequence of
>>> signature values.  The problem with just defining the extension to
>>> SIGNED is that one needs to make sure that the set of signature
>>> algorithms and parameters are also part of the data to be signed and
>>> I am not seeing that highlighted here.
>>>  
>>> Jim
>>>  
>>>  
>>> *From:* Spasm <[e-mail]
>>> <mailto:[e-mail]>> *On Behalf Of *Ryan Sleevi
>>> *Sent:* Monday, September 10, 2018 8:53 AM
>>> *To:* [e-mail] <mailto:[e-mail]>
>>> *Cc:* SPASM <[e-mail]
>>> <mailto:[e-mail]>>; [e-mail]
>>> <mailto:[e-mail]>
>>> *Subject:* Re: [lamps] Double signatures
>>>  
>>>
>>>  
>>>
>>> On Mon, Sep 10, 2018 at 10:56 AM Erik Andersen <[e-mail]
>>> <mailto:[e-mail]>> wrote:
>>>
>>>     Hi Folk,
>>>      
>>>     In ITU-T we have plans to allow for double signatures using the
>>>     SIGNED parametrized data type defined in X.509 to cope with
>>>     situation as described in the internet draft: “Multiple
>>>     Public-Key Algorithm X.509 Certificates
>>>     (draft-truskovsky-lamps-pq-hybrid-x509-01)”
>>>      
>>>     We suggest to enhance the SIGNED data type as shown below:
>>>      
>>>     *SIGNED{ToBeSigned} ::= SEQUENCE {*
>>>     *  COMPONENTS OF SIGNATURE,*
>>>     *  ......,*
>>>     *  altAlgorithmIdentifier 
>>>     AlgorithmIdentifier{{SupportedAlgorithms}} OPTIONAL,*
>>>     *  altSignature            BIT STRING OPTIONAL *
>>>     *  **} (WITH COMPONENTS {..., altAlgorithmIdentifier PRESENT,
>>>     altSignature PRESENT } |*
>>>     *     WITH COMPONENTS {..., altAlgorithmIdentifier ABSENT, 
>>>     altSignature ABSENT } )*
>>>     * *
>>>     We are open to comments. We know that IETF is not a heavy user
>>>     of this data type.
>>>      
>>>     We have no intention to use this extended data type for
>>>     certificates and CRLs.
>>>      
>>>     For your information, SIGNATURE is defined as:
>>>      
>>>     *SIGNATURE ::= SEQUENCE {*
>>>     *  algorithmIdentifier  AlgorithmIdentifier{{SupportedAlgorithms}},*
>>>     *  signature            BIT STRING,*
>>>     *  ...... }*
>>>
>>>  
>>> From the discussions in London (101), there were a number of
>>> challenges identified during the discussion
>>> - https://datatracker.ietf.org/meeting/101/materials/minutes-101-lamps-01.txt -
>>> that fundamentally questioned that approach.
>>>  
>>> Has the ITU-T addressed or resolved those concerns? Are they not
>>> applicable for some reason specific to ITU-T? 
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>

-- 
Best Regards,
Massimiliano Pala, Ph.D.
CableLabs
Principal Architect
Security Services, R&D