SSL(8) OpenBSD System Manager's Manual SSL(8)NAMEssl - details for libssl and libcrypto
DESCRIPTION
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).
RANDOM DATA SOURCE
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
applications such as ssh(1), and httpd(8).
It is important to remember when using a random data source for
certificate 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 result. 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
certificates. The arandom(4) device ensures that no two users on the
same machine will see the same data. See openssl(1) for more information
on how to use different sources of random data.
SERVER CERTIFICATES
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
secure.
GENERATING RSA SERVER CERTIFICATES FOR WEB SERVERS
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
httpd(8)GENERATING DSA SERVER CERTIFICATES
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
certificate 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
USING SSL/TLS WITH SENDMAIL
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.
SEE ALSOopenssl(1), ssh(1), ssl(3), arandom(4), httpd(8), isakmpd(8), rc(8),
sendmail(8), sshd(8), starttls(8)HISTORY
Prior to Sept 21, 2000, there were problems shipping fully functional
implementations 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 implementations 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
without 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 exchange 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.
Predictably, RSADSI would prefer that web browsers used their patented
algorithm, 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
commercially available software. Prior to version 2.8, OpenBSD allowed
users to download RSA enabled versions of the shared libssl and libcrypto
libraries 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.
BUGS
The world needs more DSA capable SSL and SSH services.
OpenBSD 4.9 March 26, 2010 OpenBSD 4.9
