Import X509 certificate with subjectAltName (SAN) into JKS keystore

I'm using pyOpenSSL to create a X509 certifcate. I need to import this certificate into a Java JKS keystore to make it available to my Java application. This is working fine as long as I don't add a subjectAltName extension to the certificate. If the certificate has an alternative subject set, import into the JKS keystore fails:

root@51561a8a1e01:~# /opt/oracle/java/jdk64-1.8.0_92/bin/keytool -keystore keystore -storepass changeit -noprompt -importcert -alias example -file certificate.crt -v
keytool error: java.lang.Exception: Input not an X.509 certificate
java.lang.Exception: Input not an X.509 certificate
    at sun.security.tools.keytool.Main.doCommands(Main.java:1009)655)
    at sun.security.tools.keytool.Main.main(Main.java:336)
root@51561a8a1e01:~#

If I print this certificate using OpenSSL on the command line, I get this output:

root@51561a8a1e01:~# openssl x509 -in certificate.crt -text -noout
Certificate:
    Data:
        Version: 1 (0x0)
        Serial Number: 0 (0x0)
    Signature Algorithm: sha256WithRSAEncryption
        Issuer: OU=example.com, CN=my-server.example.com, O=example.com
        Validity
            Not Before: Aug 26 12:03:03 2016 GMT
            Not After : Aug 25 12:03:03 2021 GMT
        Subject: OU=example.com, CN=my-server.example.com, O=example.com
        Subject Public Key Info:
            Public Key Algorithm: rsaEncryption
                Public-Key: (2048 bit)
                Modulus:
                    00:cc:a7:53:5a:38:...:11:2f
                Exponent: 65537 (0x10001)
        X509v3 extensions:
            X509v3 Subject Alternative Name:
                DNS:localhost
    Signature Algorithm: sha256WithRSAEncryption
         ab:51:12:fb:a6:a6:...:0d:4b

That is the certificate is obviously valid. And according to oracle's documentation the Java 8 keytool should support the SubjectAlternativeName extension.

When I tried to generate everything with keytool itself - which seems to work - I noticed that the certificate generated by keytool has a second extension X509v3 Subject Key Identifier:

Certificate:
    Data:
        Version: 3 (0x2)
        Serial Number: 1510484556 (0x5a082a4c)
    Signature Algorithm: sha256WithRSAEncryption
        Issuer: O=example.com, OU=example.com, CN=my-server.example.com
        Validity
            Not Before: Aug 26 12:52:43 2016 GMT
            Not After : Nov 24 12:52:43 2016 GMT
        Subject: O=example.com, OU=example.com, CN=my-server.example.com
        Subject Public Key Info:
            Public Key Algorithm: rsaEncryption
                Public-Key: (2048 bit)
                Modulus:
                    00:99:b6:b1:11:a6:...:7b:39
                Exponent: 65537 (0x10001)
        X509v3 extensions:
            X509v3 Subject Alternative Name:
                DNS:localhost
            X509v3 Subject Key Identifier:
                66:75:AD:7A:A5:19:AB:43:DE:55:E4:A7:4F:C2:3D:53:55:49:CE:48
    Signature Algorithm: sha256WithRSAEncryption
         50:7c:fe:c8:5d:1b:...:da:27

Do I need to add this extension to my certificate using pyOpenSSL as well. But what would be the correct value?!

Solution

Well, just after writing down everything for this question I noticed that there is a second difference between the certificate generated with pyOpenSSL and the keytool one. The keytool certificate states Version: 3 (0x2) while the other one says Version: 1 (0x0).

I'm not too much into the X509 specs but as the extensions are all prefixed with X509v3 I'd guess that extension support is not available for version 1 certificates.

And after adapting my python code to set the version to 3 (actually 2 as version is 0 based), import into keytool works as expected:

_cert = OpenSSL.crypto.X509()
_cert.set_version(2)
...