[security-dev 00226]: X509KeyManager alias choice based on temporary socket

Bruno Harbulot Bruno.Harbulot at manchester.ac.uk
Wed Jul 9 06:02:00 PDT 2008


I'm trying to use an X509KeyManager to choose which certificate a server 
presents depending on which IP address the socket is listening on.

Let's suppose I have two certificates (+private keys) for 
host1.example.org ( and host2.example.com (, and that 
the clients are going to check the name of the hostname against the name 
in the certificate. This should work fine since there are two distinct 
IP addresses, one for each certificate.

The Java server I'm running is configured with a single SSLContext, 
which is set up with a KeyStore that contains two pairs of private keys 
and certificates. This SSLContext is also set up to use a custom 
X509KeyManager, which I was planning to use to choose which of the two 
aliases (and therefore certificates) should be used depending on the socket.
This server starts up two SSLServerSockets, one with local address and the other one with local address (same port, but 
this shouldn't really matter).

I initially thought that "chooseServerAlias(String keyType, Principal[] 
issuers, Socket socket)" would give me the server socket used and thus I 
would be able to pick the alias based on "socket.getLocalAddress()".

Unfortunately, it turns out that the socket passed to chooseServerAlias 
is not the socket that is actually used. Its address is always, 
regardless of the IP address the actual listening socket has been bound to.

I've traced the call to chooseServerAlias to:

Looking at com.sun.net.ssl.internal.ssl.SSLServerSocketImpl (in 
openjdk-6-src-b10_30_may_2008.tar.gz and 
openjdk-7-ea-src-b30-03_jul_2008.zip), it turns out that the choice of 
the certificate is based on a temporary socket, which is initialised 
with settings based on the actual socket (cipher suites, etc.), but not 
the local address or port. (Code fragment at the end of this e-mail.)

It is done by design? Any idea how it would be possible to choose a 
certificate based on which IP address is used otherwise?

Best wishes,


====== This is a short extract of 
com.sun.net.ssl.internal.ssl.SSLServerSocketImpl (line count will differ 
depending on the version, but it's towards the end of the file) =====

      * This is a sometimes helpful diagnostic check that is performed
      * once for each ServerSocket to verify that the initial set of
      * enabled suites are capable of supporting a successful handshake.
     private void checkEnabledSuites() throws IOException {
         // We want to report an error if no cipher suites were actually
         // enabled, since this is an error users are known to make.  Then
         // they get vastly confused by having clients report an error!
         synchronized (this) {
             if (checkedEnabled) {
             if (useServerMode == false) {

             SSLSocketImpl tmp = new SSLSocketImpl(sslContext, 
                          enabledCipherSuites, doClientAuth,
                          enableSessionCreation, enabledProtocols);

             ServerHandshaker handshaker = tmp.getServerHandshaker();

             for (Iterator t = enabledCipherSuites.iterator(); 
t.hasNext(); ) {
                 CipherSuite suite = (CipherSuite)t.next();
                 if (handshaker.trySetCipherSuite(suite)) {
                     checkedEnabled = true;

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