Why does SSL handshake give 'Could not generat

Question

When I make an SSL connection with some IRC servers (but not others - presumably due to the server's preferred encryption method) I get the following exception:

Caused by: java.lang.RuntimeException: Could not generate DH keypair
    at com.sun.net.ssl.internal.ssl.DHCrypt.<init>(DHCrypt.java:106)
    at com.sun.net.ssl.internal.ssl.ClientHandshaker.serverKeyExchange(ClientHandshaker.java:556)
    at com.sun.net.ssl.internal.ssl.ClientHandshaker.processMessage(ClientHandshaker.java:183)
    at com.sun.net.ssl.internal.ssl.Handshaker.processLoop(Handshaker.java:593)
    at com.sun.net.ssl.internal.ssl.Handshaker.process_record(Handshaker.java:529)
    at com.sun.net.ssl.internal.ssl.SSLSocketImpl.readRecord(SSLSocketImpl.java:893)
    at com.sun.net.ssl.internal.ssl.SSLSocketImpl.performInitialHandshake(SSLSocketImpl.java:1138)
    at com.sun.net.ssl.internal.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:1165)
    ... 3 more

Final cause:

Caused by: java.security.InvalidAlgorithmParameterException: Prime size must be multiple of 64, and can only range from 512 to 1024 (inclusive)
    at com.sun.crypto.provider.DHKeyPairGenerator.initialize(DashoA13*..)
    at java.security.KeyPairGenerator$Delegate.initialize(KeyPairGenerator.java:627)
    at com.sun.net.ssl.internal.ssl.DHCrypt.<init>(DHCrypt.java:100)
    ... 10 more

An example of a server that demonstrates this problem is aperture.esper.net:6697 (this is an IRC server). An example of a server that does not demonstrate the problem is kornbluth.freenode.net:6697. [Not surprisingly, all servers on each network share the same respective behaviour.]

My code (which as noted does work when connecting to some SSL servers) is:

    SSLContext sslContext = SSLContext.getInstance("SSL");
    sslContext.init(null, trustAllCerts, new SecureRandom());
    s = (SSLSocket)sslContext.getSocketFactory().createSocket();
    s.connect(new InetSocketAddress(host, port), timeout);
    s.setSoTimeout(0);
    ((SSLSocket)s).startHandshake();

It's that last startHandshake that throws the exception. And yes there is some magic going on with the 'trustAllCerts'; that code forces the SSL system not to validate certs. (So... not a cert problem.)

Obviously one possibility is that esper's server is misconfigured, but I searched and didn't find any other references to people having problems with esper's SSL ports, and 'openssl' connects to it (see below). So I'm wondering if this is a limitation of Java default SSL support, or something. Any suggestions?

Here's what happens when I connect to aperture.esper.net 6697 using 'openssl' from commandline:

~ $ openssl s_client -connect aperture.esper.net:6697
CONNECTED(00000003)
depth=0 /C=GB/ST=England/L=London/O=EsperNet/OU=aperture.esper.net/CN=*.esper.net/emailAddress=[e-mail]
verify error:num=18:self signed certificate
verify return:1
depth=0 /C=GB/ST=England/L=London/O=EsperNet/OU=aperture.esper.net/CN=*.esper.net/emailAddress=[e-mail]
verify return:1
---
Certificate chain
 0 s:/C=GB/ST=England/L=London/O=EsperNet/OU=aperture.esper.net/CN=*.esper.net/emailAddress=[e-mail]
   i:/C=GB/ST=England/L=London/O=EsperNet/OU=aperture.esper.net/CN=*.esper.net/emailAddress=[e-mail]
---
Server certificate
-----BEGIN CERTIFICATE-----
[There was a certificate here, but I deleted it to save space]
-----END CERTIFICATE-----
subject=/C=GB/ST=England/L=London/O=EsperNet/OU=aperture.esper.net/CN=*.esper.net/emailAddress=[e-mail]
issuer=/C=GB/ST=England/L=London/O=EsperNet/OU=aperture.esper.net/CN=*.esper.net/emailAddress=[e-mail]
---
No client certificate CA names sent
---
SSL handshake has read 2178 bytes and written 468 bytes
---
New, TLSv1/SSLv3, Cipher is DHE-RSA-AES256-SHA
Server public key is 2048 bit
Secure Renegotiation IS supported
Compression: NONE
Expansion: NONE
SSL-Session:
    Protocol  : TLSv1
    Cipher    : DHE-RSA-AES256-SHA
    Session-ID: 51F1D40A1B044700365D3BD1C61ABC745FB0C347A334E1410946DCB5EFE37AFD
    Session-ID-ctx: 
    Master-Key: DF8194F6A60B073E049C87284856B5561476315145B55E35811028C4D97F77696F676DB019BB6E271E9965F289A99083
    Key-Arg   : None
    Start Time: 1311801833
    Timeout   : 300 (sec)
    Verify return code: 18 (self signed certificate)
---

As noted, after all that, it does connect successfully which is more than you can say for my Java app.

Should it be relevant, I'm using OS X 10.6.8, Java version 1.6.0_26.

Answer 1

I used to get a similar error accessing svn.apache.org with java SVN clients using an IBM JDK. Currently, svn.apache.org users the clients cipher preferences.

After running just once with a packet capture / javax.net.debug=ALL I was able to blacklist just a single DHE cipher and things work for me (ECDHE is negotiated instead).

.../java/jre/lib/security/java.security:
    jdk.tls.disabledAlgorithms=SSL_DHE_RSA_WITH_AES_256_CBC_SHA

A nice quick fix when it is not easy to change the client.

Answer 2

If you are still bitten by this issue AND you are using Apache httpd v> 2.4.7, try this: http://httpd.apache.org/docs/current/ssl/ssl_faq.html#javadh

copied from the url:

Beginning with version 2.4.7, mod_ssl will use DH parameters which include primes with lengths of more than 1024 bits. Java 7 and earlier limit their support for DH prime sizes to a maximum of 1024 bits, however.

If your Java-based client aborts with exceptions such as java.lang.RuntimeException: Could not generate DH keypair and java.security.InvalidAlgorithmParameterException: Prime size must be multiple of 64, and can only range from 512 to 1024 (inclusive), and httpd logs tlsv1 alert internal error (SSL alert number 80) (at LogLevel info or higher), you can either rearrange mod_ssl's cipher list with SSLCipherSuite (possibly in conjunction with SSLHonorCipherOrder), or you can use custom DH parameters with a 1024-bit prime, which will always have precedence over any of the built-in DH parameters.

To generate custom DH parameters, use the

openssl dhparam 1024

command. Alternatively, you can use the following standard 1024-bit DH parameters from RFC 2409, section 6.2:

-----BEGIN DH PARAMETERS-----
MIGHAoGBAP//////////yQ/aoiFowjTExmKLgNwc0SkCTgiKZ8x0Agu+pjsTmyJR
Sgh5jjQE3e+VGbPNOkMbMCsKbfJfFDdP4TVtbVHCReSFtXZiXn7G9ExC6aY37WsL
/1y29Aa37e44a/taiZ+lrp8kEXxLH+ZJKGZR7OZTgf//////////AgEC
-----END DH PARAMETERS-----

Add the custom parameters including the "BEGIN DH PARAMETERS" and "END DH PARAMETERS" lines to the end of the first certificate file you have configured using the SSLCertificateFile directive.

---

I am using java 1.6 on client side, and it solved my issue. I didn't lowered the cipher suites or like, but added a custom generated DH param to the cert file..

Answer 3

The problem is the prime size. The maximum-acceptable size that Java accepts is 1024 bits. This is a known issue (see JDK-6521495).

The bug report that I linked to mentions a workaround using BouncyCastle's JCE implementation. Hopefully that should work for you.

UPDATE

This was reported as bug JDK-7044060 and fixed recently.

Note, however, that the limit was only raised to 2048 bit. For sizes > 2048 bit, there is JDK-8072452 - Remove the maximum prime size of DH Keys; the fix appears to be for 9.

Answer 4

Here is my solution (java 1.6), also would be interested why I had to do this:

I noticed from the javax.security.debug=ssl, that sometimes the used cipher suite is TLS_DHE_... and sometime it is TLS_ECDHE_.... The later would happen if I added BouncyCastle. If TLS_ECDHE_ was selected, MOST OF the time it worked, but not ALWAYS, so adding even BouncyCastle provider was unreliable (failed with same error, every other time or so). I guess somewhere in the Sun SSL implementation sometimes it choose DHE, sometimes it choose ECDHE.

So the solution posted here relies on removing TLS_DHE_ ciphers completely. NOTE: BouncyCastle is NOT required for the solution.

So create the server certification file by:

echo |openssl s_client -connect example.org:443 2>&1 |sed -ne '/-BEGIN CERTIFICATE-/,/-END CERTIFICATE-/p'

Save this as it will be referenced later, than here is the solution for an SSL http get, excluding the TLS_DHE_ cipher suites.

package org.example.security;

import java.io.BufferedInputStream;
import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.InetAddress;
import java.net.Socket;
import java.net.URL;
import java.net.UnknownHostException;
import java.security.KeyStore;
import java.security.cert.Certificate;
import java.security.cert.CertificateFactory;
import java.security.cert.X509Certificate;
import java.util.ArrayList;
import java.util.List;

import javax.net.ssl.HttpsURLConnection;
import javax.net.ssl.SSLContext;
import javax.net.ssl.SSLParameters;
import javax.net.ssl.SSLSocket;
import javax.net.ssl.SSLSocketFactory;
import javax.net.ssl.TrustManagerFactory;

import org.apache.log4j.Logger;

public class SSLExcludeCipherConnectionHelper {

    private Logger logger = Logger.getLogger(SSLExcludeCipherConnectionHelper.class);

    private String[] exludedCipherSuites = {"_DHE_","_DH_"};

    private String trustCert = null;

    private TrustManagerFactory tmf;

    public void setExludedCipherSuites(String[] exludedCipherSuites) {
        this.exludedCipherSuites = exludedCipherSuites;
    }

    public SSLExcludeCipherConnectionHelper(String trustCert) {
        super();
        this.trustCert = trustCert;
        //Security.addProvider(new BouncyCastleProvider());
        try {
            this.initTrustManager();
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }

    private void initTrustManager() throws Exception {
        CertificateFactory cf = CertificateFactory.getInstance("X.509");
        InputStream caInput = new BufferedInputStream(new FileInputStream(trustCert));
        Certificate ca = null;
        try {
            ca = cf.generateCertificate(caInput);
            logger.debug("ca=" + ((X509Certificate) ca).getSubjectDN());
        } finally {
            caInput.close();
        }

        // Create a KeyStore containing our trusted CAs
        KeyStore keyStore = KeyStore.getInstance("jks");
        keyStore.load(null, null);
        keyStore.setCertificateEntry("ca", ca);

        // Create a TrustManager that trusts the CAs in our KeyStore
        String tmfAlgorithm = TrustManagerFactory.getDefaultAlgorithm();
        tmf = TrustManagerFactory.getInstance(tmfAlgorithm);
        tmf.init(keyStore);
    }

    public String get(URL url) throws Exception {
        // Create an SSLContext that uses our TrustManager
        SSLContext context = SSLContext.getInstance("TLS");
        context.init(null, tmf.getTrustManagers(), null);
        SSLParameters params = context.getSupportedSSLParameters();
        List<String> enabledCiphers = new ArrayList<String>();
        for (String cipher : params.getCipherSuites()) {
            boolean exclude = false;
            if (exludedCipherSuites != null) {
                for (int i=0; i<exludedCipherSuites.length && !exclude; i++) {
                    exclude = cipher.indexOf(exludedCipherSuites[i]) >= 0;
                }
            }
            if (!exclude) {
                enabledCiphers.add(cipher);
            }
        }
        String[] cArray = new String[enabledCiphers.size()];
        enabledCiphers.toArray(cArray);

        // Tell the URLConnection to use a SocketFactory from our SSLContext
        HttpsURLConnection urlConnection =
            (HttpsURLConnection)url.openConnection();
        SSLSocketFactory sf = context.getSocketFactory();
        sf = new DOSSLSocketFactory(sf, cArray);
        urlConnection.setSSLSocketFactory(sf);
        BufferedReader in = new BufferedReader(new InputStreamReader(urlConnection.getInputStream()));
        String inputLine;
        StringBuffer buffer = new StringBuffer();
        while ((inputLine = in.readLine()) != null) 
            buffer.append(inputLine);
        in.close();

        return buffer.toString();
    }

    private class DOSSLSocketFactory extends javax.net.ssl.SSLSocketFactory {

        private SSLSocketFactory sf = null;
        private String[] enabledCiphers = null;

        private DOSSLSocketFactory(SSLSocketFactory sf, String[] enabledCiphers) {
            super();
            this.sf = sf;
            this.enabledCiphers = enabledCiphers;
        }

        private Socket getSocketWithEnabledCiphers(Socket socket) {
            if (enabledCiphers != null && socket != null && socket instanceof SSLSocket)
                ((SSLSocket)socket).setEnabledCipherSuites(enabledCiphers);

            return socket;
        }

        @Override
        public Socket createSocket(Socket s, String host, int port,
                boolean autoClose) throws IOException {
            return getSocketWithEnabledCiphers(sf.createSocket(s, host, port, autoClose));
        }

        @Override
        public String[] getDefaultCipherSuites() {
            return sf.getDefaultCipherSuites();
        }

        @Override
        public String[] getSupportedCipherSuites() {
            if (enabledCiphers == null)
                return sf.getSupportedCipherSuites();
            else
                return enabledCiphers;
        }

        @Override
        public Socket createSocket(String host, int port) throws IOException,
                UnknownHostException {
            return getSocketWithEnabledCiphers(sf.createSocket(host, port));
        }

        @Override
        public Socket createSocket(InetAddress address, int port)
                throws IOException {
            return getSocketWithEnabledCiphers(sf.createSocket(address, port));
        }

        @Override
        public Socket createSocket(String host, int port, InetAddress localAddress,
                int localPort) throws IOException, UnknownHostException {
            return getSocketWithEnabledCiphers(sf.createSocket(host, port, localAddress, localPort));
        }

        @Override
        public Socket createSocket(InetAddress address, int port,
                InetAddress localaddress, int localport) throws IOException {
            return getSocketWithEnabledCiphers(sf.createSocket(address, port, localaddress, localport));
        }

    }
}

Finally here is how it is used (certFilePath if the path of the certificate saved from openssl):

try {
            URL url = new URL("https://www.example.org?q=somedata");            
            SSLExcludeCipherConnectionHelper sslExclHelper = new SSLExcludeCipherConnectionHelper(certFilePath);
            logger.debug(
                    sslExclHelper.get(url)
            );
        } catch (Exception ex) {
            ex.printStackTrace();
        }

Answer 5

It is possible that you have incorrect Maven dependencies. You must find these libraries in Maven dependency hierarchy:

bcprov-jdk14, bcpkix-jdk14, bcmail-jdk14

If you have these dependencies that is the error, and you should do this:

Add the dependency:

<dependency>
    <groupId>org.bouncycastle</groupId>
    <artifactId>bcmail-jdk15on</artifactId>
    <version>1.59</version>
</dependency>

Exclude these dependencies from the artifact that included the wrong dependencies, in my case it is:

<dependency>
    <groupId>com.lowagie</groupId>
    <artifactId>itext</artifactId>
    <version>2.1.7</version>
    <exclusions>
        <exclusion>
            <groupId>org.bouncycastle</groupId>
            <artifactId>bctsp-jdk14</artifactId>                
        </exclusion>
        <exclusion>
            <groupId>bouncycastle</groupId>
            <artifactId>bcprov-jdk14</artifactId>               
        </exclusion>
        <exclusion>
            <groupId>bouncycastle</groupId>
            <artifactId>bcmail-jdk14</artifactId>               
        </exclusion>
    </exclusions>       
</dependency>

Answer 6

You can disable DHE completely in your jdk, edit jre/lib/security/java.security and make sure DHE is disabled, eg. like

jdk.tls.disabledAlgorithms=SSLv3, DHE.