Makes perfectly sense. Thank you. > Am 25.03.2020 um 18:49 schrieb Viktor Dukhovni <openssl-users@xxxxxxxxxxxx>: > > On Wed, Mar 25, 2020 at 05:47:01PM +0100, Dirk wrote: > >>>> My expectation (maybe wrong) is that the serial and the issuer name belong to >>>> the same X509 certificate that the key id belongs to. >>> >>> Your expectation is "wrong". The issuer DN in the AKID is in fact >>> supposed to be the issuer's issuer. It would be redundant to >>> encode the issuer DN there, it is already present in the EE >>> certificate. >> >> Thank you Victor. Can you point me to the rfc that defines this? > > You could just save time and take my word for it, based on the logical > argument that the issuer public key is identified by the serial number > and DN of the CA that signed its certificate (the combination required > to be unique) and that repeating the EE issuer DN would be redundant. > The text in RFC 5280 is not terribly clear, but is basically a brief > restatement of X.509. > > If you really want to puzzle over more text see (page 24, physical page > 34 of): > > http://handle.itu.int/11.1002/1000/9590-en?locatt=format:pdf > > 8.2.2.1 Authority key identifier extension > > This field, which may be used as either a certificate extension or > CRL extension, identifies the public key to be used to verify the > signature on this certificate or CRL. It enables distinct keys used > by the same CA to be distinguished (e.g., as key updating occurs). > This field is defined as follows: > > authorityKeyIdentifier EXTENSION ::= { > SYNTAX AuthorityKeyIdentifier IDENTIFIED BY id-ce-authorityKeyIdentifier > } > > AuthorityKeyIdentifier ::= SEQUENCE { > keyIdentifier [0] KeyIdentifier OPTIONAL > authorityCertIssuer [1] GeneralNames OPTIONAL > authorityCertSerialNumber [2] CertificateSerialNumber OPTIONAL } > ( WITH COMPONENTS {..., authorityCertIssuer PRESENT, authorityCertSerialNumber PRESENT} | > WITH COMPONENTS {..., authorityCertIssuer ABSENT, authorityCertSerialNumber ABSENT} ) > > KeyIdentifier ::= OCTET STRING > > The key may be identified by an explicit key identifier in the > keyIdentifier component, by identification of a certificate for the > key (giving certificate issuer in the authorityCertIssuer component > and certificate serial number in the authorityCertSerialNumber > component), or by both explicit key identifier and identification of > a certificate for the key. If both forms of identification are used > then the certificate or CRL issuer shall ensure they are consistent. > A key identifier shall be unique with respect to all key identifiers > for the issuing authority for the certificate or CRL containing the > extension. An implementation which supports this extension is not > required to be able to process all name forms in the > authorityCertIssuer component. (See 8.3.2.1 for details of the > GeneralNames type.) > > Certification authorities shall assign certificate serial numbers > such that every (issuer, certificate serial number) pair uniquely > identifies a single certificate. The keyIdentifier form can be used > to select CA certificates during path construction. The > authorityCertIssuer, authoritySerialNumber pair can only be used to > provide preference to one certificate over others during path > construction. > > This extension is always non-critical. > > -- > Viktor.
