15.8. OpenSSL

15.8. OpenSSL
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Written by Tom Rhodes.

The OpenSSL toolkit is included in FreeBSD. It provides an encryption transport layer on top of the normal communications layer, allowing it to be intertwined with many network applications and services.

Some uses of OpenSSL may include encrypted authentication of mail clients and web based transactions such as credit card payments. Many ports such as www/apache22, and mail/claws-mail offer compilation support for building with OpenSSL.

Note:

In most cases, the Ports Collection will attempt to build the security/openssl port unless WITH_OPENSSL_BASE is explicitly set to “yes”.

The version of OpenSSL included in FreeBSD supports Secure Sockets Layer v2/v3 (SSLv2/SSLv3) and Transport Layer Security v1 (TLSv1) network security protocols and can be used as a general cryptographic library.

Note:

While OpenSSL supports the IDEA algorithm, it is disabled by default due to United States patents. To use it, the license should be reviewed and, if the restrictions are acceptable, the MAKE_IDEA variable must be set in /etc/make.conf.

One of the most common uses of OpenSSL is to provide certificates for use with software applications. These certificates ensure that the credentials of the company or individual are valid and not fraudulent. If the certificate in question has not been verified by a “Certificate Authority” (CA), a warning is produced. A CA is a company, such as VeriSign, signs certificates in order to validate the credentials of individuals or companies. This process has a cost associated with it and is not a requirement for using certificates; however, it can put users at ease.

15.8.1. Generating Certificates

To generate a certificate, the following command is available:

# openssl req -new -nodes -out req.pem -keyout cert.pem Generating a 1024 bit RSA private key ................++++++ .......................................++++++ writing new private key to 'cert.pem' ----- You are about to be asked to enter information that will be incorporated into your certificate request. What you are about to enter is what is called a Distinguished Name or a DN. There are quite a few fields but you can leave some blank For some fields there will be a default value, If you enter '.', the field will be left blank. ----- Country Name (2 letter code) [AU]:US State or Province Name (full name) [Some-State]:PA Locality Name (eg, city) []:Pittsburgh Organization Name (eg, company) [Internet Widgits Pty Ltd]:My Company Organizational Unit Name (eg, section) []:Systems Administrator Common Name (eg, YOUR name) []:localhost.example.org Email Address []:trhodes@FreeBSD.org Please enter the following 'extra' attributes to be sent with your certificate request A challenge password []:SOME PASSWORD An optional company name []:Another Name

Notice the response directly after the “Common Name” prompt shows a domain name. This prompt requires a server name to be entered for verification purposes and placing anything but a domain name yields a useless certificate. Other options, such as the expire time and alternate encryption algorithms, are available. A complete list of options is described in openssl(1).

Two files should now exist in the directory in which this command was issued. The certificate request, req.pem, may be sent to a CA who will validate the entered credentials, sign the request, and return the signed certificate. The second file is named cert.pem and is the private key for the certificate and should be protected at all costs. If this falls in the hands of others it can be used to impersonate the user or the server.

In cases where a signature from a CA is not required, a self signed certificate can be created. First, generate the RSA key:

# openssl dsaparam -rand -genkey -out myRSA.key 1024

Next, generate the CA key:

# openssl gendsa -des3 -out myca.key myRSA.key

Use this key to create the certificate:

# openssl req -new -x509 -days 365 -key myca.key -out new.crt

Two new files should appear in the directory: a certificate authority signature file, myca.key and the certificate itself, new.crt. These should be placed in a directory, preferably under /etc, which is readable only by root. Permissions of 0700 are appropriate and can be set using chmod(1).

15.8.2. Using Certificates

One use for a certificate is to encrypt connections to the Sendmail MTA. This prevents the use of clear text authentication for users who send mail via the local MTA.

Note:

Some MUAs will display error if the user has not installed the certificate locally. Refer to the documentation included with the software for more information on certificate installation.

To configure Sendmail, the following lines should be placed in the local .mc file:

dnl SSL Options define(`confCACERT_PATH',`/etc/certs')dnl define(`confCACERT',`/etc/certs/new.crt')dnl define(`confSERVER_CERT',`/etc/certs/new.crt')dnl define(`confSERVER_KEY',`/etc/certs/myca.key')dnl define(`confTLS_SRV_OPTIONS', `V')dnl

In this example, /etc/certs/ stores the certificate and key files locally. After saving the edits, rebuild the local .cf file by typing make install within /etc/mail. Follow that up with make restart which should start the Sendmail daemon.

If all went well, there will be no error messages in /var/log/maillog and Sendmail will show up in the process list.

For a simple test, connect to the mail server using telnet(1):

# telnet example.com 25 Trying 192.0.34.166... Connected to example.com. Escape character is '^]'. 220 example.com ESMTP Sendmail 8.12.10/8.12.10; Tue, 31 Aug 2004 03:41:22 -0400 (EDT) ehlo example.com 250-example.com Hello example.com [192.0.34.166], pleased to meet you 250-ENHANCEDSTATUSCODES 250-PIPELINING 250-8BITMIME 250-SIZE 250-DSN 250-ETRN 250-AUTH LOGIN PLAIN 250-STARTTLS 250-DELIVERBY 250 HELP quit 221 2.0.0 example.com closing connection Connection closed by foreign host.

If the “STARTTLS” line appears in the output, everything is working correctly.

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