Re: [lamps] Double signatures

Jim Schaad <> Wed, 12 September 2018 14:59 UTC

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From: Jim Schaad <>
To: 'Russ Housley' <>, 'Massimiliano Pala' <>
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Subject: Re: [lamps] Double signatures
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There are two easy ways to indicate this.  The first would be to allocate multiple oids





The second would be to put a int value before the sequence of signature oids with the number of signatures that needed to validate so you could do 3 of n need to validate.





From: Spasm <> On Behalf Of Russ Housley
Sent: Wednesday, September 12, 2018 5:13 AM
To: Massimiliano Pala <>
Cc: SPASM <>rg>; Erik Andersen <>
Subject: Re: [lamps] Double signatures




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.




On Sep 11, 2018, at 4:45 PM, Max Pala < <> > 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?









On Sep 11, 2018, at 8:38 AM, Tim Hollebeek < <>> 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).




From: Santosh Chokhani < <>> 
Sent: Tuesday, September 11, 2018 10:29 AM
To: Tim Hollebeek < <>>gt;; 'Erik Andersen' < <>>gt;; 'SPASM' < <>>gt;;  <>
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 [ <>] On Behalf Of Tim Hollebeek
Sent: Tuesday, September 11, 2018 10:03 AM
To: Erik Andersen < <>>gt;; 'SPASM' < <>>gt;;  <>
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…




From: Spasm < <>> On Behalf Of Erik Andersen
Sent: Tuesday, September 11, 2018 3:10 AM
To: 'SPASM' < <>>gt;;  <>
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.




Fra: Spasm [ <>] På vegne af Santosh Chokhani
Sendt: 10 September 2018 19:18
Til: 'Jim Schaad' < <>>gt;; 'Ryan Sleevi' < <>>gt;;  <>
Cc: 'SPASM' < <>>gt;;  <>
Emne: Re: [lamps] Double signatures


Why not let algorithm identifier dictate the number of signatures and their syntax?


From: Spasm [ <>] On Behalf Of Jim Schaad
Sent: Monday, September 10, 2018 1:07 PM
To: 'Ryan Sleevi' < <>>gt;;  <>
Cc: 'SPASM' < <>>gt;;  <>
Subject: Re: [lamps] Double signatures




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.




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.





From: Spasm < <>> On Behalf Of Ryan Sleevi
Sent: Monday, September 10, 2018 8:53 AM
To:  <>
Cc: SPASM < <>>gt;;  <>
Subject: Re: [lamps] Double signatures



On Mon, Sep 10, 2018 at 10:56 AM Erik Andersen < <>> 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:





  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:



  algorithmIdentifier  AlgorithmIdentifier{{SupportedAlgorithms}},

  signature            BIT STRING,

  ...... }


>From the discussions in London (101), there were a number of challenges identified during the discussion -  <> - 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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