SSL/TLS Strong Encryption: FAQ

Available Languages: en | + fr

+ +

+
The wise man doesn't give the right answers, +he poses the right questions.
+
-- Claude Levi-Strauss
+ +

Installation
Configuration
Certificates
The SSL Protocol
mod_ssl Support

Installation

Why do I get permission errors related to +SSLMutex when I start Apache?
Why does mod_ssl stop with the error "Failed to +generate temporary 512 bit RSA private key" when I start Apache?

+ +

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?
Which port does HTTPS use?
How do I speak HTTPS manually for testing +purposes?
Why does the connection hang when I connect to my +SSL-aware Apache server?
Why do I get ``Connection Refused'' errors, when +trying to access my newly installed Apache+mod_ssl server via HTTPS?
Why are the SSL_XXX variables not +available to my CGI & SSI scripts?
How can I switch between HTTP and HTTPS in +relative hyperlinks?

+ +

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?
Is there a difference on startup between +a non-SSL-aware Apache and an SSL-aware Apache?
How do I create a self-signed SSL +Certificate for testing purposes?
How do I create a real SSL Certificate?
How do I create and use my own Certificate +Authority (CA)?
How can I change the pass-phrase on my private +key file?
How can I get rid of the pass-phrase +dialog at Apache startup time?
How do I verify that a private key matches its +Certificate?
How can I convert a certificate from PEM to DER +format?
Why do browsers complain that they cannot +verify my server certificate?

+ +

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 2048
+
+ 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 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 2048
+
+ 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 -extensions usr_cert
+
+ 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

+ + +

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

The default certificate format for 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 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?
Why does my webserver have a higher load, now +that it serves SSL encrypted traffic?
Why do HTTPS connections to my server +sometimes take up to 30 seconds to establish a connection?
What SSL Ciphers are supported by mod_ssl?
Why do I get ``no shared cipher'' errors, when +trying to use Anonymous Diffie-Hellman (ADH) ciphers?
Why do I get a 'no shared ciphers' +error when connecting to my newly installed server?
Why can't I use SSL with name-based/non-IP-based +virtual hosts?
Is it possible to use Name-Based Virtual +Hosting to identify different SSL virtual hosts?
How do I get SSL compression working?
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?
Why do I get I/O errors when connecting via +HTTPS to an Apache+mod_ssl server with Microsoft Internet Explorer +(MSIE)?
How do I enable TLS-SRP?
Why do I get handshake failures with Java-based clients when using a certificate with more than 1024 bits?

+ +

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 SHA1
AES with SHA1
Triple-DES with SHA1

+ +

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 + extra/httpd-ssl.conf) 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.

+ + +

Is it 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).

+ +

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 preferred 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 older versions of 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 [2-5]" \
+         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.

+ + +

How do I enable TLS-SRP?

TLS-SRP (Secure Remote Password key exchange for TLS, specified in RFC 5054) + can supplement or replace certificates in authenticating an SSL connection. + To use TLS-SRP, set the + SSLSRPVerifierFile directive to + point to an OpenSSL SRP verifier file. To create the verifier file, use the + openssl tool:

+ openssl srp -srpvfile passwd.srpv -add username +

After creating this file, specify it in the SSL server configuration:

+ SSLSRPVerifierFile /path/to/passwd.srpv +

To force clients to use non-certificate TLS-SRP cipher suites, use the + following directive:

+ SSLCipherSuite "!DSS:!aRSA:SRP" +

+ + +

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

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.

+ + +

mod_ssl Support

What information resources are available in +case of mod_ssl problems?
What support contacts are available in case of +mod_ssl problems?
What information should I +provide when writing a bug report?
I had a core dump, can you help me?
How do I get a backtrace, to help find the reason +for my core dump?

+ +

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): + http://httpd.apache.org/docs/2.4/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. +

+ + +

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 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
+ + http://httpd.apache.org/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 httpd 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 httpd and 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 httpd 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. +

+ +

SSL/TLS Strong Encryption: FAQ

See also