Switch to SpeakEasy.net DSL

The Modular Manual Browser

Home Page
Manual: (OpenBSD-3.6)
Apropos / Subsearch:
optional field

SSL(8)                  OpenBSD System Manager's Manual                 SSL(8)

     ssl - details for libssl and libcrypto

     This document describes some of the issues relating to the use of the
     OpenSSL libssl and libcrypto libraries.  This document is intended as an
     overview of what the libraries do, and what uses them.

     The SSL libraries (libssl and libcrypto) implement the SSL version 2, SSL
     version 3, and TLS version 1 protocols.  SSL version 2 and 3 are most
     commonly used by the https protocol for encrypted web transactions, as
     can be done with httpd(8).  The libcrypto library is also used by various
     programs such as ssh(1), sshd(8), and isakmpd(8).

     OpenBSD uses the arandom(4) device as the default source for random data
     when needed by the routines in libcrypto and libssl.  If the arandom(4)
     device does not exist or is not readable, many of the routines will fail.
     This is most commonly seen by users as the RSA routines failing in appli-
     cations such as ssh(1), and httpd(8).

     It is important to remember when using a random data source for certifi-
     cate and key generation that the random data source should not be visible
     by people who could duplicate the process and come up with the same re-
     sult.  You should ensure that nobody who you don't trust is in a position
     to read the same random data used by you to generate keys and certifi-
     cates.  The arandom(4) device ensures that no two users on the same ma-
     chine will see the same data.  See openssl(1) for more information on how
     to use different sources of random data.

     The most common uses of SSL/TLS will require you to generate a server
     certificate, which is provided by your host as evidence of its identity
     when clients make new connections.  The certificates reside in the
     /etc/ssl directory, with the keys in the /etc/ssl/private directory.

     Private keys can be encrypted using 3DES and a passphrase to protect
     their integrity should the encrypted file be disclosed.  However, it is
     important to note that encrypted server keys mean that the passphrase
     needs to be typed in every time the server is started.  If a passphrase
     is not used, you will need to be absolutely sure your key file is kept

     Generating a DSA certificate involves several steps.  First, you generate
     a DSA parameter set with a command like the following:

           # openssl dsaparam 1024 -out dsa1024.pem

     Would generate DSA parameters for 1024 bit DSA keys, and save them to the
     file dsa1024.pem.

     Once you have the DSA parameters generated, you can generate a certifi-
     cate and unencrypted private key using the command:

           # openssl req -x509 -nodes -newkey dsa:dsa1024.pem \
             -out /etc/ssl/dsacert.pem -keyout /etc/ssl/private/dsakey.pem

     To generate an encrypted private key, you would use:

           # openssl req -x509 -newkey dsa:dsa1024.pem \
             -out /etc/ssl/dsacert.pem -keyout /etc/ssl/private/dsakey.pem

     To support https transactions in httpd(8) you will need to generate an
     RSA certificate.

           # openssl genrsa -out /etc/ssl/private/server.key 1024

     Or, if you wish the key to be encrypted with a passphrase that you will
     have to type in when starting servers

           # openssl genrsa -des3 -out /etc/ssl/private/server.key 1024

     The next step is to generate a Certificate Signing Request which is used
     to get a Certifying Authority (CA) to sign your certificate.  To do this
     use the command:

           # openssl req -new -key /etc/ssl/private/server.key \
             -out /etc/ssl/private/server.csr

     This server.csr file can then be given to Certifying Authority who will
     sign the key.

     You can also sign the key yourself, using the command:

           # openssl x509 -req -days 365 -in /etc/ssl/private/server.csr \
             -signkey /etc/ssl/private/server.key -out /etc/ssl/server.crt

     With /etc/ssl/server.crt and /etc/ssl/private/server.key in place, you
     should be able to start httpd(8) with the -DSSL flag, enabling https
     transactions with your machine on port 443.

     You will most likely want to generate a self-signed certificate in the
     manner above along with your certificate signing request to test your
     server's functionality even if you are going to have the certificate
     signed by another Certifying Authority.  Once your Certifying Authority
     returns the signed certificate to you, you can switch to using the new
     certificate by replacing the self-signed /etc/ssl/server.crt with the
     certificate signed by your Certifying Authority, and then restarting

     By default, sendmail(8) expects both the keys and certificates to reside
     in /etc/mail/certs, not in the /etc/ssl directory.  The default paths may
     be overridden in the sendmail.cf file.  See starttls(8) for information
     on configuring sendmail(8) to use SSL/TLS.

     openssl(1), ssh(1), ssl(3), arandom(4), httpd(8), isakmpd(8), rc(8),
     sendmail(8), sshd(8), starttls(8)

     Prior to Sept 21, 2000, there were problems shipping fully functional im-
     plementations of these protocols, as such shipment would include shipping
     into the United States.  RSA Data Security Inc (RSADSI) held the patent
     on the RSA algorithm in the United States, and because of this, free im-
     plementations of RSA were difficult to distribute and propagate.  (The
     RSA patent was probably more effective at preventing the adoption of
     widespread international integrated crypto than the much maligned ITAR
     restrictions were).  Prior to OpenBSD 2.8, these libraries shipped with-
     out the RSA algorithm -- all such functions were stubbed to fail.  Since
     RSA is a key component of SSL version 2, this meant that SSL version 2
     would not work at all.  SSL version 3 and TLS version 1 allow for the ex-
     change of keys via mechanisms that do not involve RSA, and would work
     with the shipped version of the libraries, assuming both ends could agree
     to a cipher suite and key exchange that did not involve RSA.  Likewise,
     the SSH1 protocol in ssh(1) uses RSA, so it was similarly encumbered.

     For instance, another typical alternative is DSA, which is not encumbered
     by commercial patents (and lawyers).

     The https protocol used by web browsers (in modern incarnations) allows
     for the use of SSL version 3 and TLS version 1, which in theory allows
     for encrypted web transactions without using RSA.  Unfortunately, all the
     popular web browsers buy their cryptographic code from RSADSI.  Pre-
     dictably, RSADSI would prefer that web browsers used their patented algo-
     rithm, and thus their libraries do not implement any non-RSA cipher and
     keying combination.  The result of this was that while the https protocol
     allowed for many cipher suites that did not require the use of patented
     algorithms, it was very difficult to use these with the popular commer-
     cially available software.  Prior to version 2.8, OpenBSD allowed users
     to download RSA enabled versions of the shared libssl and libcrypto li-
     braries which allowed users to enable full function without recompiling
     the applications.  This method is now no longer needed, as the fully
     functional libraries ship with the system.  However, this entire debacle
     is worth remembering when choosing software and vendors.

     This document first appeared in OpenBSD 2.5.

     The world needs more DSA capable SSL and SSH services.

OpenBSD 3.6                   September 19, 2001                             3