How to extract CN from X509Certificate in Java?

Question

I am using a SslServerSocket and client certificates and want to extract the CN from the SubjectDN from the client's X509Certificate.

At the moment I call cert.getSubjectX500Principal().getName() but this of course gives me the total formatted DN of the client. For some reason I am just interested in the CN=theclient part of the DN. Is there a way to extract this part of the DN without parsing the String myself?

Answer 1

here is another way. the idea is that the DN you obtain is in rfc2253 format, which is the same as used for LDAP DN. So why not reuse the LDAP API?

import javax.naming.ldap.LdapName;
import javax.naming.ldap.Rdn;

String dn = x509cert.getSubjectX500Principal().getName();
LdapName ldapDN = new LdapName(dn);
for(Rdn rdn: ldapDN.getRdns()) {
    System.out.println(rdn.getType() + " -> " + rdn.getValue());
}