Re: [lamps] Double signatures

"Panos Kampanakis (pkampana)" <> Sat, 22 September 2018 03:08 UTC

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From: "Panos Kampanakis (pkampana)" <>
To: "Dr. Pala" <>, Jim Schaad <>
CC: "" <>
Thread-Topic: [lamps] Double signatures
Date: Sat, 22 Sep 2018 03:08:26 +0000
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Hi Max, Jim,

Agreed. In summary, there are too good proposals (Erik, Max’s) that can combine multiple PKs and Sigs. That would allow us to us more than one PQ algos if they are not trusted.

draft-truskovsky-lamps-pq-hybrid allows for backwards compatibility by defining one only PQ key and sig as non-critical extensions.

I wonder if the two concepts could be merged. Meaning use the composite key + sigs can non-critical extensions. Old clients disregard the PQ extensions. New clients verify the classical  and the PQ algos defined in the composite OID contained in the non-critical extension.


From: Spasm [] On Behalf Of Dr. Pala
Sent: Thursday, September 20, 2018 1:44 PM
Subject: Re: [lamps] Double signatures

Hi Panos, all,

that is correct - since the new OIDs for the Key and the Signatures would be new, clients would fail since they do not know the "composite" algorithm :D

Although developing support for it should not be too difficult, the solution it is not meant to be backward compatible as we want applications to be able to fail if they do not even know they were supposed to generate or verify multiple signatures instead of just one.

From a usage perspective, I am leaning towards the need for the owner of the certificates to generate signatures with all the keys, and for the entity that validates the signatures it should validate all the signatures it supports and may accept signatures even if it does not understand all the algorithms (this is more an application decision based on the risk and threat model).

As I said, this solution fits not only certificates, but also OCSP responses, CRLs, CMS, PKCS#7, etc. and that is part of what is interesting for us :D I still need to check what are the needed changes for other formats like PKCS#1/#8/#12 for storing the composite public and private keys (this part still missing), but I hope that solving that part will not be too difficult...


On 9/20/18 7:26 AM, Panos Kampanakis (pkampana) wrote:
Hi Max,
To rephrase Eric’s question, would the CompositeKey+CompositeSig proposal be backwards compatible with existing systems?
I mean it gives you the change to use more than one algos in case you don’t trust all of them. But an old client wouldn’t be able to just use the traditional key+sig unless he was upgraded to understand CompositeKey+CompositeSig and its OIDs, right?

From: Spasm [] On Behalf Of Erik Andersen
Sent: Friday, September 14, 2018 11:49 AM
To: 'SPASM' <><>; Directory list <><>
Subject: Re: [lamps] Double signatures

The double signature is intended as a migration tool.

In the normal operation, only one signature is used (the native signature). When it is realized that the signature algorithm will be too week i some future, the migration period starts and an alternative, assuming stronger signature is provided for those able to handle it.  Legacy systems will ignore this alternative signature. After the migration period, there will be no alternative signature and the new stronger signature will be the native signature.

Does that make sense?


Fra: Massimiliano Pala []
Sendt: 12 September 2018 23:01
Til: Russ Housley <<>>
Cc: SPASM <<>>; Erik Andersen <<>>
Emne: Re: [lamps] Double signatures

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?


On 9/12/18 6:12 AM, Russ Housley wrote:

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 <<>>; 'Erik Andersen' <<>>; 'SPASM' <<>>;<>
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 <<>>; 'SPASM' <<>>;<>
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' <<>>;<>
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' <<>>; 'Ryan Sleevi' <<>>;<>
Cc: 'SPASM' <<>>;<>
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' <<>>;<>
Cc: 'SPASM' <<>>;<>
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
Cc: SPASM <<>>;<>
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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Best Regards,
Massimiliano Pala, Ph.D.
Principal Architect
Security Services, R&D


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