client certs with no subjectName only SAN

[Erwann Abalea]

Bonjour,

Having a critical extension adds 3 octets (the BOOLEAN tag, length=1, value=0xff). It may, as a side effect, enlarge the number of octets necessary to encode some structure size.

Remove the 2 Netscape extensions, they're way obsolete (don't know why OpenSSL keeps them by default).

If size is a hard constraint:
 - you can probably remove the emailProtection EKU (it's an OID, you'll gain 10 octets). Depending on your use-case, you may need to tweak the EKU (or remove it completely).
 - SKI and AKI extensions may not be necessary
 - Key Usage may be marked as non critical (it's a SHOULD in PKIX)

A quick reading of RFC8002 tells me that you may need to include the IssuerAltName extension as well?

Cordialement,
Erwann Abalea

Le 16/08/2019 17:11, « openssl-users au nom de Robert Moskowitz » <openssl-users-bounces at openssl.org au nom de rgm at htt-consult.com> a écrit :

    Viktor,
    
    
    On 8/16/19 8:41 AM, Viktor Dukhovni wrote:
    >> On Aug 16, 2019, at 6:13 AM, Salz, Rich via openssl-users <openssl-users at openssl.org> wrote:
    >>
    >> subjectAltName is rarely marked as critical; sec 4.2.1.6 of PKIX says "SHOULD mark subjectAltName as non-critical"
    > This is wrong.  When the subject DN is empty, the subjectAltName should be
    > marked as critical.  IIRC some Java implementations reject the certificate
    > otherwise.
    
    I have just created a client cert with empty subjectName and critical 
    subjectAltName.  Interestingly, it is 4 bytes larger than the earlier 
    non-critical SAN cert.  See below for the output of the cert.
    
    >> I can believe that OpenSSL doesn't support empty subjectName's.  An empty one, with no relative disintuished name components, is not the same as not present.
    > OpenSSL supports empty (empty RDN sequence) subject DNs.
    > The "-subj /" option is one way to make that happen.
    >
    > Empty is of course different from "absent", which is not
    > possible, since the subject DN is a required component of
    > an X.509 certificate.
    
    I now have it clear that Empty SN is NOT a cert with NO SN.  It is there 
    with null content.
    
    Thank you all.
    
    $ openssl x509 -noout -text -in $dir/certs/device2.cert.pem
    Certificate:
         Data:
             Version: 3 (0x2)
             Serial Number:
                 c9:8f:b2:7b:e1:95:74:d0
             Signature Algorithm: ED25519
             Issuer: CN = 2001:24:28:14::/64
             Validity
                 Not Before: Aug 16 14:54:58 2019 GMT
                 Not After : Aug 25 14:54:58 2020 GMT
             Subject:
             Subject Public Key Info:
                 Public Key Algorithm: ED25519
                     ED25519 Public-Key:
                     pub:
                         69:4f:1c:77:56:69:3a:cd:86:c4:3a:b0:67:b9:50:
                         c3:12:9c:6f:85:65:a0:8f:fa:b5:74:b1:c4:56:f8:
                         4c:a5
             X509v3 extensions:
                 X509v3 Basic Constraints:
                     CA:FALSE
                 Netscape Cert Type:
                     SSL Client, S/MIME
                 Netscape Comment:
                     OpenSSL Generated Client Certificate
                 X509v3 Subject Key Identifier:
    8A:8D:18:B6:F7:70:7D:17:64:AA:2F:C7:FF:1F:C2:30:E2:D8:56:DD
                 X509v3 Authority Key Identifier:
    keyid:B1:45:18:9B:33:82:6C:74:29:69:2A:15:93:3B:1C:31:D2:37:D6:CA
    
                 X509v3 Key Usage: critical
                     Digital Signature, Non Repudiation, Key Encipherment
                 X509v3 Extended Key Usage:
                     TLS Web Client Authentication, E-mail Protection
                 X509v3 Subject Alternative Name: critical
                     IP Address:2001:24:28:14:2B6E:2C43:A2D8:507C
         Signature Algorithm: ED25519
              01:54:3e:d2:21:36:27:57:f2:da:d7:ee:42:ec:8f:05:99:b1:
              4b:de:2c:c4:3b:95:6f:ba:f6:25:a5:10:bb:2d:5c:9b:15:46:
              dc:67:ea:b4:74:df:a6:52:60:6f:cd:06:af:f4:69:5f:37:1a:
              ba:1a:b4:17:c0:bb:0f:da:be:02