June 18, 2011, 1:58 a.m.
posted by unixgeek
Create Your Own Certificate Authority
Sign your own certificates to use in securing your network.
SSL certificates are usually thought of as being used for secure communications over the HTTP protocol. However, they are also useful in providing both a means for authentication and a means for initiating key exchange for a myriad of other services where encryption is desired, such as POP and IMAP [Hack #54], SMTP [Hack #55], IPsec [Hack #93], and, of course, SSL tunnels [Hack #100]. To make the best use of SSL, you will need to properly manage your own certificates.
If an SSL client needs to verify the authenticity of an SSL server, the cert used by the server needs to be signed by a Certificate Authority (CA) that is already trusted by the client. Well-known CAs (such as Thawte and VeriSign) exist to serve as authoritative, trusted third parties for authentication. They are in the business of signing SSL certificates that are used on sites dealing with sensitive information (such as account numbers or passwords).
If a trusted authority has signed a site's SSL certificate, presumably it is possible to verify the identity of a server supplying that cert's credentials. However, for anything other than e-commerce applications, a self-signed certificate is usually sufficient for gaining all of the security advantages that SSL provides. Of course, an authority that the client recognizes must sign even a self-signed cert.
Creating the CA
To establish your new Certificate Authority, first change to the /misc directory under wherever OpenSSL is installed (/System/Library/OpenSSL on Mac OS X; /usr/ssl or /usr/local/ssl on most Linux systems). Then, use these commands:
$./CA.pl -newca CA certificate filename (or enter to create) Making CA certificate ... Generating a 1024 bit RSA private key ..........++++++ .....................++++++ writing new private key to './demoCA/private/cakey.pem' Enter PEM pass phrase: Verifying - Enter PEM pass phrase: ----- 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) :US State or Province Name (full name) :Colorado Locality Name (eg, city) :Denver Organization Name (eg, company) :NonExistant Enterprises Organizational Unit Name (eg, section) :IT Services Common Name (eg, fully qualified host name) :ca.nonexistantdomain.com Email Address :[email protected]
Note that you don't necessarily need root permissions, but you will need write permissions on the current directory.
Congratulations! You're the proud owner of your very own Certificate Authority. Take a look around:
$ ls -l demoCA/ total 16 -rw-r--r-- 1 andrew andrew 1399 3 Dec 19:52 cacert.pem drwxr-xr-x 2 andrew andrew 68 3 Dec 19:49 certs drwxr-xr-x 2 andrew andrew 68 3 Dec 19:49 crl -rw-r--r-- 1 andrew andrew 0 3 Dec 19:49 index.txt drwxr-xr-x 2 andrew andrew 68 3 Dec 19:49 newcerts drwxr-xr-x 3 andrew andrew 102 3 Dec 19:49 private -rw-r--r-- 1 andrew andrew 3 3 Dec 19:49 serial
The public key for your new CA is contained in cacert.pem, and the private key is in private/cakey.pem. You can now use this private key to sign other SSL certs.
By default, CA.pl creates keys that are good for only one year. To change this behavior, edit CA.pl and change the line that reads:
Alternatively, you can forego CA.pl altogether and generate the public and private keys manually with a command like this:
$ openssl req -new -x509 -keyout cakey.pem -out cakey.pem -days 3650
This creates a key pair that is good for the next 10 years (to change that period, use a different argument to the -days switch). Additionally, you should change the private key's permissions to 600, to ensure that it is protected from being read by anyone.
So far, you've only created the Certificate Authority. To actually create keys that you can use with your services, you need to create a certificate-signing request and a key. Again, this can be done easily with CA.pl. First, create a certificate-signing request:
$ ./CA.pl -newreq-nodes Generating a 1024 bit RSA private key ...++++++ ...............................................++++++ writing new private key to 'newreq.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]:Colorado Locality Name (eg, city) :Denver Organization Name (eg, company) [Internet Widgits Pty Ltd]:NonExistant Enterprises Organizational Unit Name (eg, section) :IT Services Common Name (eg, YOUR name) :mail.nonexistantdomain.com Email Address :[email protected] Please enter the following 'extra' attributes to be sent with your certificate request A challenge password : An optional company name :NonExistant Enterprises Request (and private key) is in newreq.pem
If you want to encrypt the private key, you can use the -newreq switch in place of -newreq-nodes. However, if you encrypt the private key, you will have to enter the password for it each time the service that uses it is started. If you decide not to use an encrypted private key, be extremely cautious with your private key, as anyone who can obtain a copy of it can impersonate your server.
Now, to actually sign the request and generate the signed certificate, issue this command:
$ ./CA.pl -sign Using configuration from /System/Library/OpenSSL/openssl.cnf Enter pass phrase for ./demoCA/private/cakey.pem: Check that the request matches the signature Signature ok Certificate Details: Serial Number: 1 (0x1) Validity Not Before: Dec 3 09:05:08 2003 GMT Not After : Dec 3 09:05:08 2004 GMT Subject: countryName = US stateOrProvinceName = Colorado localityName = Denver organizationName = NonExistant Enterprises organizationalUnitName = IT Services commonName = mail.nonexistantdomain.com emailAddress = [email protected] X509v3 extensions: X509v3 Basic Constraints: CA:FALSE Netscape Comment: OpenSSL Generated Certificate X509v3 Subject Key Identifier: 94:0F:E9:F5:22:40:2C:71:D0:A7:5C:65:02:3E:BC:D8:DB:10:BD:88 X509v3 Authority Key Identifier: keyid:7E:AF:2D:A4:39:37:F5:36:AE:71:2E:09:0E:49:23:70:61:28:5F:4A DirName:/C=US/ST=Colorado/L=Denver/O=NonExistant Enterprises/OU=IT Services/ CN=Certificate Administration/[email protected] serial:00 Certificate is to be certified until Dec 7 09:05:08 2004 GMT (365 days) Sign the certificate? [y/n]:y 1 out of 1 certificate requests certified, commit? [y/n]:y Write out database with 1 new entries Data Base Updated Signed certificate is in newcert.pem
Now you can set up keys in this manner for each server that needs to provide an SSL-encrypted service. It is easier to do this if you designate a single workstation to maintain the CA and all the files associated with it. Don't forget to distribute your CA cert [Hack #70] to programs that need to trust it.