Re: Managing Long-Lived CA certs

Hi Eric,

thanks, however this does not solve the issue I am trying to address - 
it would be great if we would have it scoped. For example (not aiming at 
correctness here.. :D):

privateKeyUsageTypes ::= CHOICE {
    anyPurpose,
    certificateSigning,
    ...
}

scopedPrivateKeyUsagePeriod ::= SEQUENCE {
    scope           privateKeyUsageTypes,
    notBefore   [0] GeneralizedTime OPTIONAL,
    notAfter    [1] GeneralizedTime OPTIONAL
}

privateKeyUsageRestrictions ::= SET OF scopedPrivateKeyUsagePeriod

Of course, this is just an example :-D

Cheers,
Max

On 7/17/17 5:04 PM, Erik Andersen wrote:
>
> Hi Massimiliano,
>
> What about the private key usage period extension. It was clarified in 
> the latest edition of X.509:
>
>
>         9.2.2.5 Private key usage period extension
>
> This extension indicates the period of use of the private key 
> corresponding to the certified public key. It is applicable only for 
> private key used for creating digital signatures. This extension is 
> defined as follows:
>
> privateKeyUsagePeriod EXTENSION ::= {
>
>   SYNTAX         PrivateKeyUsagePeriod
>
>   IDENTIFIED BY  id-ce-privateKeyUsagePeriod }
>
> PrivateKeyUsagePeriod ::= SEQUENCE {
>
>   notBefore  [0]  GeneralizedTime OPTIONAL,
>
>   notAfter   [1]  GeneralizedTime OPTIONAL,
>
>   ... }
>
>   (WITH COMPONENTS {..., notBefore  PRESENT } |
>
>    WITH COMPONENTS {..., notAfter   PRESENT } )
>
> The notBefore component indicates the earliest date and time at which 
> the private key may be used for signing. If the notBefore component is 
> not present, then no information is provided as to when the period of 
> valid use of the private key commences beyond that specified in the 
> validity component of the public-key certificate. The notAfter 
> component indicates the latest date and time at which the private key 
> may be used for signing. If the notAfter component is not present then 
> no information is provided as to when the period of valid use of the 
> private key concludes beyond that specified in the validity component 
> of the public-key certificate.
>
> This extension shall always be flagged as non-critical.
>
> NOTE 1 – The period of valid use of the private key may be different 
> from the certified validity of the public key as indicated by the 
> public-key certificate validity period. The usage period for the 
> private key used for signing is typically shorter than that for the 
> public key used for verifying the signature.
>
> NOTE  2 – The period of use of the private key corresponding to a 
> public key can only be enforced if both the private key and the 
> corresponding public-key certificate are placed in a tamper-resistant 
> hardware module that contains a reliable clock synchronized with UTC. 
> When this is not the case, a signer may avoid using a signing private 
> key up to the very end of the validity period of the public-key 
> certificate. This is one possible use of this extension.
>
> NOTE 3 – In general, this Specification does not associate any 
> semantic with this extension. Any particular use of this extension 
> will have to specify the semantic associated with that usage.
>
> *Fra:*pkix [mailto:[email protected]] *På vegne af *Dr. Pala
> *Sendt:* 17 July 2017 16:20
> *Til:* [email protected]
> *Emne:* [pkix] Managing Long-Lived CA certs
>
> Hi PKIX,
>
> I have a small question for the list regarding long-lived CA 
> certificates. Especially in the context of device certificates, we 
> often see the use of extra long-lived certificates for Root and Sub 
> CAs (e.g., 35+ years) combined with limited key sizes (e.g., p256).
>
> Until we have a supported mechanism for reprovisioning devices (...), 
> one possible solution for limiting the exposure of the private key 
> would be to have a scoped certificate issuance period.
>
> What I am thinking about would be adding an extension that says: "This 
> CA can issue certificates from up to 5 years from the validFrom, after 
> this, just use it to provide revocation information". This might 
> provide some protection in case the CA key is compromised after the 
> initial 5 years of validity (e.g., certificates issued after that date 
> shall be rejected).
>
> Does such extension exists today ? If not, could this be some work for 
> LAMPS/SPASM WG ?
>
> Cheers,
> Max
>
> -- 
>
> Best Regards,
>
> Massimiliano Pala, Ph.D.
> OpenCA Labs Director
>
> OpenCA Logo
>
>
>
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