Network Security Hacks [Electronic resources] نسخه متنی

Hack 45 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 #47],
SMTP
[Hack #48], IPSec (see Chapter 6), and, of course, SSL tunnels [Hack #76] .
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 Certificate Authorities
(such as Thawte and VeriSign) exist to serve as an authoritative,
trusted third party 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
site's SSL certificate is signed by a trusted
authority, then 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. But even a self-signed
cert must be signed by an authority that the client recognizes.

OpenSSL, a free SSL
implementation, is perfectly capable of generating everything you
need to run your own Certificate Authority. The
CA.pl utility makes the process very simple.

In these examples, you'll need to type anything in
boldface, and enter passwords wherever appropriate (they
don't echo to the screen). To establish your new
Certificate Authority, first change to the misc/
directory under wherever OpenSSL is installed
(/System/Library/OpenSSL/ on OpenBSD;
/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 []:certadmin@nonexistantdomain.com

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 Certificate
Authority 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 will create keys that are good
for only one year. To change this behavior, edit
CA.pl and change the line that reads:

$DAYS="-days 365";

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 will create a key pair that is good for the next 10 years, which
can of course be changed by using 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, we have 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, a
certificate-signing request is created:

$ ./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 []:postmaster@nonexistantdomain.com
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 wish 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:

$ ./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              = postmaster@nonexistantdomain.com
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/emailAddress=certadmin@nonexistantdomain.com
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 certificate authority
and all the files associated with it. Don't forget
to distribute your CA cert to programs that need to trust it [Hack #46] .