SSL/TLS Strong Encryption: FAQ

About The Module

What is the history of mod_ssl?

The mod_ssl v1 package was initially created in April 1998 by Ralf S. Engelschall via porting Ben Laurie's Apache-SSL 1.17 source patches for Apache 1.2.6 to Apache 1.3b6. Because of conflicts with Ben Laurie's development cycle it then was re-assembled from scratch for Apache 1.3.0 by merging the old mod_ssl 1.x with the newer Apache-SSL 1.18. From this point on mod_ssl lived its own life as mod_ssl v2. The first publicly released version was mod_ssl 2.0.0 from August 10th, 1998.

After US export restrictions on cryptographic software were loosened, mod_ssl became part of the Apache HTTP Server with the release of Apache httpd 2.

Is mod_ssl affected by the Wassenaar Arrangement?

First, let us explain what Wassenaar and its Arrangement on Export Controls for Conventional Arms and Dual-Use Goods and Technologies is: This is a international regime, established in 1995, to control trade in conventional arms and dual-use goods and technology. It replaced the previous CoCom regime. Further details on both the Arrangement and its signatories are available at http://www.wassenaar.org/.

In short, the aim of the Wassenaar Arrangement is to prevent the build up of military capabilities that threaten regional and international security and stability. The Wassenaar Arrangement controls the export of cryptography as a dual-use good, that is, something that has both military and civilian applications. However, the Wassenaar Arrangement also provides an exemption from export controls for mass-market software and free software.

In the current Wassenaar List of Dual Use Goods and Technologies And Munitions, under GENERAL SOFTWARE NOTE (GSN) it says The Lists do not control "software" which is either: 1. [...] 2. "in the public domain". And under DEFINITIONS OF TERMS USED IN THESE LISTS we find In the public domain defined as "technology" or "software" which has been made available without restrictions upon its further dissemination. Note: Copyright restrictions do not remove "technology" or "software" from being "in the public domain".

So, both mod_ssl and OpenSSL are in the public domain for the purposes of the Wassenaar Arrangement and its List of Dual Use Goods and Technologies And Munitions List, and thus not affected by its provisions.

Installation

Why do I get permission errors related to SSLMutex when I start Apache?

Errors such as ``mod_ssl: Child could not open SSLMutex lockfile /opt/apache/logs/ssl_mutex.18332 (System error follows) [...] System: Permission denied (errno: 13)'' are usually caused by overly restrictive permissions on the parent directories. Make sure that all parent directories (here /opt, /opt/apache and /opt/apache/logs) have the x-bit set for, at minimum, the UID under which Apache's children are running (see the User directive).

Why does mod_ssl stop with the error "Failed to generate temporary 512 bit RSA private key" when I start Apache?

Cryptographic software needs a source of unpredictable data to work correctly. Many open source operating systems provide a "randomness device" that serves this purpose (usually named /dev/random). On other systems, applications have to seed the OpenSSL Pseudo Random Number Generator (PRNG) manually with appropriate data before generating keys or performing public key encryption. As of version 0.9.5, the OpenSSL functions that need randomness report an error if the PRNG has not been seeded with at least 128 bits of randomness.

To prevent this error, mod_ssl has to provide enough entropy to the PRNG to allow it to work correctly. This can be done via the SSLRandomSeed directive.

Configuration

Is it possible to provide HTTP and HTTPS from the same server?

Yes. HTTP and HTTPS use different server ports (HTTP binds to port 80, HTTPS to port 443), so there is no direct conflict between them. You can either run two separate server instances bound to these ports, or use Apache's elegant virtual hosting facility to create two virtual servers, both served by the same instance of Apache - one responding over HTTP to requests on port 80, and the other responding over HTTPS to requests on port 443.

Which port does HTTPS use?

You can run HTTPS on any port, but the standards specify port 443, which is where any HTTPS compliant browser will look by default. You can force your browser to look on a different port by specifying it in the URL. For example, if your server is set up to serve pages over HTTPS on port 8080, you can access them at https://example.com:8080/

How do I speak HTTPS manually for testing purposes?

While you usually just use

$ telnet localhost 80 GET / HTTP/1.0

for simple testing of Apache via HTTP, it's not so easy for HTTPS because of the SSL protocol between TCP and HTTP. With the help of OpenSSL's s_client command, however, you can do a similar check via HTTPS:

$ openssl s_client -connect localhost:443 -state -debug GET / HTTP/1.0

Before the actual HTTP response you will receive detailed information about the SSL handshake. For a more general command line client which directly understands both HTTP and HTTPS, can perform GET and POST operations, can use a proxy, supports byte ranges, etc. you should have a look at the nifty cURL tool. Using this, you can check that Apache is responding correctly to requests via HTTP and HTTPS as follows:

$ curl http://localhost/ $ curl https://localhost/

Why does the connection hang when I connect to my SSL-aware Apache server?

This can happen when you try to connect to a HTTPS server (or virtual server) via HTTP (eg, using http://example.com/ instead of https://example.com). It can also happen when trying to connect via HTTPS to a HTTP server (eg, using https://example.com/ on a server which doesn't support HTTPS, or which supports it on a non-standard port). Make sure that you're connecting to a (virtual) server that supports SSL.

Why do I get ``Connection Refused'' messages, when trying to access my newly installed Apache+mod_ssl server via HTTPS?

This error can be caused by an incorrect configuration. Please make sure that your Listen directives match your <VirtualHost> directives. If all else fails, please start afresh, using the default configuration provided by mod_ssl.

Why are the `SSL_XXX` variables not available to my CGI & SSI scripts?

Please make sure you have ``SSLOptions +StdEnvVars'' enabled for the context of your CGI/SSI requests.

How can I switch between HTTP and HTTPS in relative hyperlinks?

Usually, to switch between HTTP and HTTPS, you have to use fully-qualified hyperlinks (because you have to change the URL scheme). Using mod_rewrite however, you can manipulate relative hyperlinks, to achieve the same effect.

RewriteEngine on RewriteRule ^/(.*)_SSL$ https://%{SERVER_NAME}/$1 [R,L] RewriteRule ^/(.*)_NOSSL$ http://%{SERVER_NAME}/$1 [R,L]

This rewrite ruleset lets you use hyperlinks of the form <a href="document.html_SSL">, to switch to HTTPS in a relative link. (Replace SSL with NOSSL to switch to HTTP.)

Certificates

What are RSA Private Keys, CSRs and Certificates?

An RSA private key file is a digital file that you can use to decrypt messages sent to you. It has a public component which you distribute (via your Certificate file) which allows people to encrypt those messages to you.

A Certificate Signing Request (CSR) is a digital file which contains your public key and your name. You send the CSR to a Certifying Authority (CA), who will convert it into a real Certificate, by signing it.

A Certificate contains your RSA public key, your name, the name of the CA, and is digitally signed by the CA. Browsers that know the CA can verify the signature on that Certificate, thereby obtaining your RSA public key. That enables them to send messages which only you can decrypt.

See the Introduction chapter for a general description of the SSL protocol.

Is there a difference on startup between a non-SSL-aware Apache and an SSL-aware Apache?

Yes. In general, starting Apache with mod_ssl built-in is just like starting Apache without it. However, if you have a passphrase on your SSL private key file, a startup dialog will pop up which asks you to enter the pass phrase.

Having to manually enter the passphrase when starting the server can be problematic - for example, when starting the server from the system boot scripts. In this case, you can follow the steps below to remove the passphrase from your private key. Bear in mind that doing so brings additional security risks - proceed with caution!

How do I create a self-signed SSL Certificate for testing purposes?

Make sure OpenSSL is installed and in your PATH.
Run the following command, to create server.key and server.crt files:
$ openssl req -new -x509 -nodes -out server.crt -keyout server.key
These can be used as follows in your httpd.conf file:
```
             SSLCertificateFile    /path/to/this/server.crt
             SSLCertificateKeyFile /path/to/this/server.key
```
It is important that you are aware that this server.key does not have any passphrase. To add a passphrase to the key, you should run the following command, and enter & verify the passphrase as requested.

$ openssl rsa -des3 -in server.key -out server.key.new
$ mv server.key.new server.key

Please backup the server.key file, and the passphrase you entered, in a secure location.

How do I create a real SSL Certificate?

Here is a step-by-step description:

Make sure OpenSSL is installed and in your PATH.
Create a RSA private key for your Apache server (will be Triple-DES encrypted and PEM formatted):

$ openssl genrsa -des3 -out server.key 1024

Please backup this server.key file and the pass-phrase you entered in a secure location. You can see the details of this RSA private key by using the command:

$ openssl rsa -noout -text -in server.key

If necessary, you can also create a decrypted PEM version (not recommended) of this RSA private key with:

$ openssl rsa -in server.key -out server.key.unsecure
Create a Certificate Signing Request (CSR) with the server RSA private key (output will be PEM formatted):

$ openssl req -new -key server.key -out server.csr

Make sure you enter the FQDN ("Fully Qualified Domain Name") of the server when OpenSSL prompts you for the "CommonName", i.e. when you generate a CSR for a website which will be later accessed via https://www.foo.dom/, enter "www.foo.dom" here. You can see the details of this CSR by using

$ openssl req -noout -text -in server.csr
You now have to send this Certificate Signing Request (CSR) to a Certifying Authority (CA) to be signed. Once the CSR has been signed, you will have a real Certificate, which can be used by Apache. You can have a CSR signed by a commercial CA, or you can create your own CA to sign it.
Commercial CAs usually ask you to post the CSR into a web form, pay for the signing, and then send a signed Certificate, which you can store in a server.crt file. For more information about commercial CAs see the following locations:
1. Verisign
  http://digitalid.verisign.com/server/apacheNotice.htm
2. Thawte
  http://www.thawte.com/
3. CertiSign Certificadora Digital Ltda.
  http://www.certisign.com.br
4. IKS GmbH
  http://www.iks-jena.de/leistungen/ca/
5. Uptime Commerce Ltd.
  http://www.uptimecommerce.com
6. BelSign NV/SA
  http://www.belsign.be
For details on how to create your own CA, and use this to sign a CSR, see below.
Once your CSR has been signed, you can see the details of the Certificate as follows:

$ openssl x509 -noout -text -in server.crt
You should now have two files: server.key and server.crt. These can be used as follows in your httpd.conf file:
```
       SSLCertificateFile    /path/to/this/server.crt
       SSLCertificateKeyFile /path/to/this/server.key
```
The server.csr file is no longer needed.

How do I create and use my own Certificate Authority (CA)?

The short answer is to use the CA.sh or CA.pl script provided by OpenSSL. Unless you have a good reason not to, you should use these for preference. If you cannot, you can create a self-signed Certificate as follows:

Create a RSA private key for your server (will be Triple-DES encrypted and PEM formatted):

$ openssl genrsa -des3 -out server.key 1024

Please backup this server.key file and the pass-phrase you entered in a secure location. You can see the details of this RSA private key by using the command:

$ openssl rsa -noout -text -in server.key

If necessary, you can also create a decrypted PEM version (not recommended) of this RSA private key with:

$ openssl rsa -in server.key -out server.key.unsecure
Create a self-signed Certificate (X509 structure) with the RSA key you just created (output will be PEM formatted):

$ openssl req -new -x509 -nodes -sha1 -days 365 -key server.key -out server.crt

This signs the server CSR and results in a server.crt file.
You can see the details of this Certificate using:

$ openssl x509 -noout -text -in server.crt

How can I change the pass-phrase on my private key file?

You simply have to read it with the old pass-phrase and write it again, specifying the new pass-phrase. You can accomplish this with the following commands:

$ openssl rsa -des3 -in server.key -out server.key.new
$ mv server.key.new server.key

The first time you're asked for a PEM pass-phrase, you should enter the old pass-phrase. After that, you'll be asked again to enter a pass-phrase - this time, use the new pass-phrase. If you are asked to verify the pass-phrase, you'll need to enter the new pass-phrase a second time.

How can I get rid of the pass-phrase dialog at Apache startup time?

The reason this dialog pops up at startup and every re-start is that the RSA private key inside your server.key file is stored in encrypted format for security reasons. The pass-phrase is needed to decrypt this file, so it can be read and parsed. Removing the pass-phrase removes a layer of security from your server - proceed with caution!

Remove the encryption from the RSA private key (while keeping a backup copy of the original file):

$ cp server.key server.key.org
$ openssl rsa -in server.key.org -out server.key
Make sure the server.key file is only readable by root:

$ chmod 400 server.key

Now server.key contains an unencrypted copy of the key. If you point your server at this file, it will not prompt you for a pass-phrase. HOWEVER, if anyone gets this key they will be able to impersonate you on the net. PLEASE make sure that the permissions on this file are such that only root or the web server user can read it (preferably get your web server to start as root but run as another user, and have the key readable only by root).

As an alternative approach you can use the ``SSLPassPhraseDialog exec:/path/to/program'' facility. Bear in mind that this is neither more nor less secure, of course.

How do I verify that a private key matches its Certificate?

A private key contains a series of numbers. Two of these numbers form the "public key", the others are part of the "private key". The "public key" bits are included when you generate a CSR, and subsequently form part of the associated Certificate.

To check that the public key in your Certificate matches the public portion of your private key, you simply need to compare these numbers. To view the Certificate and the key run the commands:

$ openssl x509 -noout -text -in server.crt
$ openssl rsa -noout -text -in server.key

The `modulus' and the `public exponent' portions in the key and the Certificate must match. As the public exponent is usually 65537 and it's difficult to visually check that the long modulus numbers are the same, you can use the following approach:

$ openssl x509 -noout -modulus -in server.crt | openssl md5
$ openssl rsa -noout -modulus -in server.key | openssl md5

This leaves you with two rather shorter numbers to compare. It is, in theory, possible that these numbers may be the same, without the modulus numbers being the same, but the chances of this are overwhelmingly remote.

Should you wish to check to which key or certificate a particular CSR belongs you can perform the same calculation on the CSR as follows:

$ openssl req -noout -modulus -in server.csr | openssl md5

Why do connections fail with an "alert bad certificate" error?

Errors such as OpenSSL: error:14094412: SSL routines:SSL3_READ_BYTES:sslv3 alert bad certificate in the SSL logfile, are usually caused by a browser which is unable to handle the server certificate/private-key. For example, Netscape Navigator 3.x is unable to handle RSA key lengths not equal to 1024 bits.

Why does my 2048-bit private key not work?

The private key sizes for SSL must be either 512 or 1024 bits, for compatibility with certain web browsers. A keysize of 1024 bits is recommended because keys larger than 1024 bits are incompatible with some versions of Netscape Navigator and Microsoft Internet Explorer, and with other browsers that use RSA's BSAFE cryptography toolkit.

Why is client authentication broken after upgrading from SSLeay version 0.8 to 0.9?

The CA certificates under the path you configured with SSLCACertificatePath are found by SSLeay through hash symlinks. These hash values are generated by the `openssl x509 -noout -hash' command. However, the algorithm used to calculate the hash for a certificate changed between SSLeay 0.8 and 0.9. You will need to remove all old hash symlinks and create new ones after upgrading. Use the Makefile provided by mod_ssl.

How can I convert a certificate from PEM to DER format?

The default certificate format for SSLeay/OpenSSL is PEM, which is simply Base64 encoded DER, with header and footer lines. For some applications (e.g. Microsoft Internet Explorer) you need the certificate in plain DER format. You can convert a PEM file cert.pem into the corresponding DER file cert.der using the following command: $ openssl x509 -in cert.pem -out cert.der -outform DER

Why can't I find the `getca` or `getverisign` programs mentioned by Verisign, for installing my Verisign certificate?

Verisign has never provided specific instructions for Apache+mod_ssl. The instructions provided are for C2Net's Stronghold (a commercial Apache based server with SSL support).

To install your certificate, all you need to do is to save the certificate to a file, and give the name of that file to the SSLCertificateFile directive. You will also need to give it the key file. For more information, see the SSLCertificateKeyFile directive.

Can I use the Server Gated Cryptography (SGC) facility (aka Verisign Global ID) with mod_ssl?

Yes. mod_ssl has included support for the SGC facility since version 2.1. No special configuration is required - just use the Global ID as your server certificate. The step up of the clients is then automatically handled by mod_ssl at run-time.

Why do browsers complain that they cannot verify my server certificate?

One reason this might happen is because your server certificate is signed by an intermediate CA. Various CAs, such as Verisign or Thawte, have started signing certificates not with their root certificate but with intermediate certificates.

Intermediate CA certificates lie between the root CA certificate (which is installed in the browsers) and the server certificate (which you installed on the server). In order for the browser to be able to traverse and verify the trust chain from the server certificate to the root certificate it needs need to be given the intermediate certificates. The CAs should be able to provide you such intermediate certificate packages that can be installed on the server.

You need to include those intermediate certificates with the SSLCertificateChainFile directive.

The SSL Protocol

Why do I get lots of random SSL protocol errors under heavy server load?

There can be a number of reasons for this, but the main one is problems with the SSL session Cache specified by the SSLSessionCache directive. The DBM session cache is the most likely source of the problem, so using the SHM session cache (or no cache at all) may help.

Why does my webserver have a higher load, now that it serves SSL encrypted traffic?

SSL uses strong cryptographic encryption, which necessitates a lot of number crunching. When you request a webpage via HTTPS, everything (even the images) is encrypted before it is transferred. So increased HTTPS traffic leads to load increases.

Why do HTTPS connections to my server sometimes take up to 30 seconds to establish a connection?

This is usually caused by a /dev/random device for SSLRandomSeed which blocks the read(2) call until enough entropy is available to service the request. More information is available in the reference manual for the SSLRandomSeed directive.

What SSL Ciphers are supported by mod_ssl?

Usually, any SSL ciphers supported by the version of OpenSSL in use, are also supported by mod_ssl. Which ciphers are available can depend on the way you built OpenSSL. Typically, at least the following ciphers are supported:

RC4 with MD5
RC4 with MD5 (export version restricted to 40-bit key)
RC2 with MD5
RC2 with MD5 (export version restricted to 40-bit key)
IDEA with MD5
DES with MD5
Triple-DES with MD5

To determine the actual list of ciphers available, you should run the following:

$ openssl ciphers -v

Why do I get ``no shared cipher'' errors, when trying to use Anonymous Diffie-Hellman (ADH) ciphers?

By default, OpenSSL does not allow ADH ciphers, for security reasons. Please be sure you are aware of the potential side-effects if you choose to enable these ciphers.

In order to use Anonymous Diffie-Hellman (ADH) ciphers, you must build OpenSSL with ``-DSSL_ALLOW_ADH'', and then add ``ADH'' into your SSLCipherSuite.

Why do I get a 'no shared ciphers' error when connecting to my newly installed server?

Either you have made a mistake with your SSLCipherSuite directive (compare it with the pre-configured example in httpd.conf-dist) or you chose to use DSA/DH algorithms instead of RSA when you generated your private key and ignored or overlooked the warnings. If you have chosen DSA/DH, then your server cannot communicate using RSA-based SSL ciphers (at least until you configure an additional RSA-based certificate/key pair). Modern browsers like NS or IE can only communicate over SSL using RSA ciphers. The result is the "no shared ciphers" error. To fix this, regenerate your server certificate/key pair, using the RSA algorithm.

Why can't I use SSL with name-based/non-IP-based virtual hosts?

The reason is very technical, and a somewhat "chicken and egg" problem. The SSL protocol layer stays below the HTTP protocol layer and encapsulates HTTP. When an SSL connection (HTTPS) is established Apache/mod_ssl has to negotiate the SSL protocol parameters with the client. For this, mod_ssl has to consult the configuration of the virtual server (for instance it has to look for the cipher suite, the server certificate, etc.). But in order to go to the correct virtual server Apache has to know the Host HTTP header field. To do this, the HTTP request header has to be read. This cannot be done before the SSL handshake is finished, but the information is needed in order to complete the SSL handshake phase. See the next question for how to circumvent this issue.

Note that if you have a wildcard SSL certificate, or a certificate that has multiple hostnames on it using subjectAltName fields, you can use SSL on name-based virtual hosts without further workarounds.

Why is it not possible to use Name-Based Virtual Hosting to identify different SSL virtual hosts?

Name-Based Virtual Hosting is a very popular method of identifying different virtual hosts. It allows you to use the same IP address and the same port number for many different sites. When people move on to SSL, it seems natural to assume that the same method can be used to have lots of different SSL virtual hosts on the same server.

It is possible, but only if using a 2.2.12 or later web server, built with 0.9.8j or later OpenSSL. This is because it requires a feature that only the most recent revisions of the SSL specification added, called Server Name Indication (SNI).

Note that if you have a wildcard SSL certificate, or a certificate that has multiple hostnames on it using subjectAltName fields, you can use SSL on name-based virtual hosts without further workarounds.

The reason is that the SSL protocol is a separate layer which encapsulates the HTTP protocol. So the SSL session is a separate transaction, that takes place before the HTTP session has begun. The server receives an SSL request on IP address X and port Y (usually 443). Since the SSL request did not contain any Host: field, the server had no way to decide which SSL virtual host to use. Usually, it just used the first one it found which matched the port and IP address specified.

If you are using a version of the web server and OpenSSL that support SNI, though, and the client's browser also supports SNI, then the hostname is included in the original SSL request, and the web server can select the correct SSL virtual host.

You can, of course, use Name-Based Virtual Hosting to identify many non-SSL virtual hosts (all on port 80, for example) and then have a single SSL virtual host (on port 443). But if you do this, you must make sure to put the non-SSL port number on the NameVirtualHost directive, e.g.

NameVirtualHost 192.168.1.1:80

How do I get SSL compression working?

Although SSL compression negotiation was defined in the specification of SSLv2 and TLS, it took until May 2004 for RFC 3749 to define DEFLATE as a negotiable standard compression method.

OpenSSL 0.9.8 started to support this by default when compiled with the zlib option. If both the client and the server support compression, it will be used. However, most clients still try to initially connect with an SSLv2 Hello. As SSLv2 did not include an array of prefered compression algorithms in its handshake, compression cannot be negotiated with these clients. If the client disables support for SSLv2, either an SSLv3 or TLS Hello may be sent, depending on which SSL library is used, and compression may be set up. You can verify whether clients make use of SSL compression by logging the %{SSL_COMPRESS_METHOD}x variable.

When I use Basic Authentication over HTTPS the lock icon in Netscape browsers stays unlocked when the dialog pops up. Does this mean the username/password is being sent unencrypted?

No, the username/password is transmitted encrypted. The icon in Netscape browsers is not actually synchronized with the SSL/TLS layer. It only toggles to the locked state when the first part of the actual webpage data is transferred, which may confuse people. The Basic Authentication facility is part of the HTTP layer, which is above the SSL/TLS layer in HTTPS. Before any HTTP data communication takes place in HTTPS, the SSL/TLS layer has already completed its handshake phase, and switched to encrypted communication. So don't be confused by this icon.

Why do I get I/O errors when connecting via HTTPS to an Apache+mod_ssl server with Microsoft Internet Explorer (MSIE)?

The first reason is that the SSL implementation in some MSIE versions has some subtle bugs related to the HTTP keep-alive facility and the SSL close notify alerts on socket connection close. Additionally the interaction between SSL and HTTP/1.1 features are problematic in some MSIE versions. You can work around these problems by forcing Apache not to use HTTP/1.1, keep-alive connections or send the SSL close notify messages to MSIE clients. This can be done by using the following directive in your SSL-aware virtual host section:

SetEnvIf User-Agent ".*MSIE.*" \ nokeepalive ssl-unclean-shutdown \ downgrade-1.0 force-response-1.0

Further, some MSIE versions have problems with particular ciphers. Unfortunately, it is not possible to implement a MSIE-specific workaround for this, because the ciphers are needed as early as the SSL handshake phase. So a MSIE-specific SetEnvIf won't solve these problems. Instead, you will have to make more drastic adjustments to the global parameters. Before you decide to do this, make sure your clients really have problems. If not, do not make these changes - they will affect all your clients, MSIE or otherwise.

The next problem is that 56bit export versions of MSIE 5.x browsers have a broken SSLv3 implementation, which interacts badly with OpenSSL versions greater than 0.9.4. You can accept this and require your clients to upgrade their browsers, you can downgrade to OpenSSL 0.9.4 (not advised), or you can work around this, accepting that your workaround will affect other browsers too:

SSLProtocol all -SSLv3

will completely disables the SSLv3 protocol and allow those browsers to work. A better workaround is to disable only those ciphers which cause trouble.

SSLCipherSuite ALL:!ADH:!EXPORT56:RC4+RSA:+HIGH:+MEDIUM:+LOW:+SSLv2:+EXP

This also allows the broken MSIE versions to work, but only removes the newer 56bit TLS ciphers.

Another problem with MSIE 5.x clients is that they refuse to connect to URLs of the form https://12.34.56.78/ (where IP-addresses are used instead of the hostname), if the server is using the Server Gated Cryptography (SGC) facility. This can only be avoided by using the fully qualified domain name (FQDN) of the website in hyperlinks instead, because MSIE 5.x has an error in the way it handles the SGC negotiation.

And finally there are versions of MSIE which seem to require that an SSL session can be reused (a totally non standard-conforming behaviour, of course). Connecting with those MSIE versions only work if a SSL session cache is used. So, as a work-around, make sure you are using a session cache (see the SSLSessionCache directive).

Why do I get I/O errors, or the message "Netscape has encountered bad data from the server", when connecting via HTTPS to an Apache+mod_ssl server with Netscape Navigator?

This usually occurs when you have created a new server certificate for a given domain, but had previously told your browser to always accept the old server certificate. Once you clear the entry for the old certificate from your browser, everything should be fine. Netscape's SSL implementation is correct, so when you encounter I/O errors with Netscape Navigator it is usually caused by the configured certificates.

Why do I get handshake failures with Java-based clients when using a certificate with more than 1024 bits?

Beginning with version 2.2.30, 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.

mod_ssl Support

What information resources are available in case of mod_ssl problems?

The following information resources are available. In case of problems you should search here first.

Answers in the User Manual's F.A.Q. List (this): /docs/2.2/ssl/ssl_faq.html
First check the F.A.Q. (this text). If your problem is a common one, it may have been answered several times before, and been included in this doc.
Postings from the modssl-users Support Mailing List http://www.modssl.org/support/: Search for your problem in the archives of the modssl-users mailing list. You're probably not the first person to have had this problem!

What support contacts are available in case of mod_ssl problems?

The following lists all support possibilities for mod_ssl, in order of preference. Please go through these possibilities in this order - don't just pick the one you like the look of.

Send a Problem Report to the modssl-users Support Mailing List
modssl-users@modssl.org
This is the preferred way of submitting your problem report, because this way, others can see the problem, and learn from any answers. You must subscribe to the list first, but you can then easily discuss your problem with both the author and the whole mod_ssl user community.
Send a Problem Report to the Apache httpd Users Support Mailing List
users@httpd.apache.org
This is the second way of submitting your problem report. Again, you must subscribe to the list first, but you can then easily discuss your problem with the whole Apache httpd user community.
Write a Problem Report in the Bug Database
/bug_report.html
This is the last way of submitting your problem report. You should only do this if you've already posted to the mailing lists, and had no success. Please follow the instructions on the above page carefully.

What information should I provide when writing a bug report?

You should always provide at least the following information:

Apache and OpenSSL version information: The Apache version can be determined by running httpd -v. The OpenSSL version can be determined by running openssl version. Alternatively, if you have Lynx installed, you can run the command lynx -mime_header http://localhost/ | grep Server to gather this information in a single step.
The details on how you built and installed Apache+mod_ssl+OpenSSL: For this you can provide a logfile of your terminal session which shows the configuration and install steps. If this is not possible, you should at least provide the configure command line you used.
In case of core dumps please include a Backtrace: If your Apache+mod_ssl+OpenSSL dumps its core, please attach a stack-frame ``backtrace'' (see below for information on how to get this). This information is required in order to find a reason for your core dump.
A detailed description of your problem: Don't laugh, we really mean it! Many problem reports don't include a description of what the actual problem is. Without this, it's very difficult for anyone to help you. So, it's in your own interest (you want the problem be solved, don't you?) to include as much detail as possible, please. Of course, you should still include all the essentials above too.

I had a core dump, can you help me?

In general no, at least not unless you provide more details about the code location where Apache dumped core. What is usually always required in order to help you is a backtrace (see next question). Without this information it is mostly impossible to find the problem and help you in fixing it.

How do I get a backtrace, to help find the reason for my core dump?

Following are the steps you will need to complete, to get a backtrace:

Make sure you have debugging symbols available, at least in Apache. On platforms where you use GCC/GDB, you will have to build Apache+mod_ssl with ``OPTIM="-g -ggdb3"'' to get this. On other platforms at least ``OPTIM="-g"'' is needed.
Start the server and try to reproduce the core-dump. For this you may want to use a directive like ``CoreDumpDirectory /tmp'' to make sure that the core-dump file can be written. This should result in a /tmp/core or /tmp/httpd.core file. If you don't get one of these, try running your server under a non-root UID. Many modern kernels do not allow a process to dump core after it has done a setuid() (unless it does an exec()) for security reasons (there can be privileged information left over in memory). If necessary, you can run /path/to/httpd -X manually to force Apache to not fork.
Analyze the core-dump. For this, run gdb /path/to/httpd /tmp/httpd.core or a similar command. In GDB, all you have to do then is to enter bt, and voila, you get the backtrace. For other debuggers consult your local debugger manual.

Please note