Re: Timestamp validation checks critical flag on EKU

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Christian:

No, RFC 5280 does not obsolete RFC 3161.  RFC 5280 obsoletes RFCs 3280, 4325, and 4630.

Anyway, RFC 5280 and RFC 3161 are consistent.

RFC 5280 says that the certificate issuer can make the EKU extension critical or non-critical.

RFC 3161 says that for use with the Time-Stamp Protocol, the certificate issuer MUST make the EKU extension critical, and it MUST contain id-kp-timeStamping.

Russ



On Jan 28, 2022, at 9:56 AM, weber@xxxxxxxxxxx wrote:

Dear Russ,

thanks for your reply.

OK, i got it, but RFC 5280 obsoletes RFC 3161 and says:

4.2.1.12.  Extended Key Usage

   This extension indicates one or more purposes for which the certified
   public key may be used, in addition to or in place of the basic
   purposes indicated in the key usage extension.  In general, this
   extension will appear only in end entity certificates.  This
   extension is defined as follows:

   id-ce-extKeyUsage OBJECT IDENTIFIER ::= { id-ce 37 }

   ExtKeyUsageSyntax ::= SEQUENCE SIZE (1..MAX) OF KeyPurposeId

   KeyPurposeId ::= OBJECT IDENTIFIER

   Key purposes may be defined by any organization with a need.  Object
   identifiers used to identify key purposes MUST be assigned in
   accordance with IANA or ITU-T Recommendation X.660 [X.660].

   This extension MAY, at the option of the certificate issuer, be
   either critical or non-critical.

   If the extension is present, then the certificate MUST only be used
   for one of the purposes indicated.  If multiple purposes are
   indicated the application need not recognize all purposes indicated,
   as long as the intended purpose is present.  Certificate using
   applications MAY require that the extended key usage extension be
   present and that a particular purpose be indicated in order for the
   certificate to be acceptable to that application.

So what?

BTW: The further obsoletions RFC i.e. Updated by: 6818, 8398, 8399
do not affect RCF 5280 in this matter.

The main question remains: How to handle this issue?

Thanks In Advance
--
Christian Weber
Am 28.01.2022 um 13:58 schrieb Russ Housley:
RFC 3161 says:

2.3. Identification of the TSA

   The TSA MUST sign each time-stamp message with a key reserved
   specifically for that purpose.  A TSA MAY have distinct private keys,
   e.g., to accommodate different policies, different algorithms,
   different private key sizes or to increase the performance.  The
   corresponding certificate MUST contain only one instance of the
   extended key usage field extension as defined in [RFC2459] Section
   4.2.1.13 with KeyPurposeID having value:

   id-kp-timeStamping.  This extension MUST be critical.

   The following object identifier identifies the KeyPurposeID having
   value id-kp-timeStamping.

   id-kp-timeStamping OBJECT IDENTIFIER ::= {iso(1)
                   identified-organization(3) dod(6)
                   internet(1) security(5) mechanisms(5) pkix(7)
                   kp (3) timestamping (8)}


On Jan 28, 2022, at 6:25 AM, weber@xxxxxxxxxxx wrote:

Dear OpenSSL users,

recently we checked an older timestamp using the OpenSSL Library version 1.1.1i.
The check revealed, that the timestamp verification failed.

Digging into the code we found that if an eku entry for timestamping is preset
it is expected to be marked critical (see v3_purp.c:798 ff.).

Thats's not the case for the timetamp cert in use.

We couldn'f find any source that enforces the critical flag on eku timestamp entries.
RFC 5280 says, that makring the EKU as critical is deliberate tu the issuer.

Any thoughts or pointer to the mentioned requirement?

Thanks in advance
--
Christian Weber

    

--
Christian Weber
Entwicklung - Verteilte Systeme
mailto:Weber@xxxxxxxxxxx
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