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Overview
The following
is an extremely simplified view of how SSL is implemented and what
part the certificate plays in the entire process.
Normal web traffic is sent unencrypted over the Internet. That is,
anyone with access to the right tools can snoop all of that traffic.
Obviously, this can lead to problems, especially where security and
privacy is necessary, such as in credit card data and bank
transactions. The Secure Socket Layer is used to encrypt the data
stream between the web server and the web client (the browser).
SSL makes use of what is known as asymmetric cryptography, commonly
referred to as public key cryptography (PKI). With public key
cryptography, two keys are created, one public, one private. Anything
encrypted with either key can only be decrypted with its corresponding
key. Thus if a message or data stream were encrypted with the server's
private key, it can be decrypted only using its corresponding public
key, ensuring that the data only could have come from the server.
If SSL utilizes public key cryptography to encrypt the data stream
traveling over the Internet, why is a certificate necessary? The
technical answer to that question is that a certificate is not really
necessary - the data is secure and cannot easily be decrypted by a
third party. However, certificates do serve a crucial role in the
communication process. The certificate, signed by a trusted
Certificate Authority (CA), ensures that the certificate holder is
really who he claims to be. Without a trusted signed certificate, your
data may be encrypted, however, the party you are communicating with
may not be whom you think. Without certificates, impersonation attacks
would be much more common.
Step 1: Generate a
Private Key
The openssl toolkit is used
to generate an RSA Private Key and CSR (Certificate Signing
Request). It can also be used to generate self-signed certificates
which can be used for testing purposes or internal usage.
The first step is to create your
RSA Private Key. This key is a 1024 bit RSA key which is encrypted using
Triple-DES and stored in a PEM format so that it is readable as ASCII
text.
openssl genrsa -des3 -out server.key 1024
Generating RSA private key, 1024 bit long
modulus
.........................................................++++++
........++++++
e is 65537 (0x10001)
Enter PEM pass phrase:
Verifying password - Enter PEM pass phrase:
Step 2: Generate a CSR (Certificate Signing Request)
Once the private key is generated a Certificate
Signing Request can be generated. The CSR is then used in one of two
ways. Ideally, the CSR will be sent to a Certificate Authority, such as
Thawte or Verisign who will verify the identity of the requestor and
issue a signed certificate. The second option is to self-sign the
CSR, which will be demonstrated in the next section.
During the generation of the CSR, you will be prompted
for several pieces of information. These are the X.509 attributes of the
certificate. One of the prompts will be for "Common Name (e.g., YOUR
name)". It is important that this field be filled in with the fully
qualified domain name of the server to be protected by SSL. If the
website to be protected will be https://public.akadia.com, then enter
public.akadia.com at this prompt. The command to generate the CSR is as
follows:
openssl req -new -key server.key -out server.csr
Country Name (2 letter code) [GB]:CH
State or Province Name (full name) [Berkshire]:Bern
Locality Name (eg, city) [Newbury]:Oberdiessbach
Organization Name (eg, company) [My Company Ltd]:Akadia
AG
Organizational Unit Name (eg, section) []:Information
Technology
Common Name (eg, your name or your server's
hostname) []:public.akadia.com
Email Address []:martin.zahn@akadia.com
Please enter the following 'extra' attributes
to be sent with your certificate request
A challenge password []:
An optional company name []:
Step 3: Remove Passphrase from Key
One unfortunate side-effect of the pass-phrased
private key is that Apache will ask for the pass-phrase each time the
web server is started. Obviously this is not necessarily convenient
as someone will not always be around to type in the pass-phrase, such as
after a reboot or crash. mod_ssl includes the ability to use an external
program in place of the built-in pass-phrase dialog, however, this is
not necessarily the most secure option either. It is possible to
remove the Triple-DES encryption from the key, thereby no longer
needing to type in a pass-phrase. If the private key is no longer
encrypted, it is critical that this file only be readable by the root
user! If your system is ever compromised and a third party obtains your
unencrypted private key, the corresponding certificate will need to be
revoked. With that being said, use the following command to remove the
pass-phrase from the key:
cp server.key server.key.org
openssl rsa -in server.key.org -out server.key
The newly created server.key file has no more passphrase in it.
-rw-r--r-- 1 root root 745 Jun
29 12:19 server.csr
-rw-r--r-- 1 root root 891 Jun 29 13:22 server.key
-rw-r--r-- 1 root root 963 Jun 29 13:22 server.key.org
Step 4: Generating a Self-Signed Certificate
At this point you will need to generate a self-signed certificate
because you either don't plan on having your certificate signed by a
CA, or you wish to test your new SSL implementation while the CA is
signing your certificate. This temporary certificate will generate an
error in the client browser to the effect that the signing certificate
authority is unknown and not trusted.
To generate a temporary certificate which is good for 365 days,
issue the following command:
openssl x509 -req -days 365 -in server.csr
-signkey server.key -out server.crt
Signature ok
subject=/C=CH/ST=Bern/L=Oberdiessbach/O=Akadia AG/OU=Information
Technology/CN=public.akadia.com/Email=martin.zahn@akadia.com
Getting Private key
Step 5: Installing the Private Key and Certificate
When Apache with mod_ssl is installed, it creates several
directories in the Apache config directory. The location of this
directory will differ depending on how Apache was compiled.
cp server.crt /usr/local/apache/conf/ssl.crt
cp server.key /usr/local/apache/conf/ssl.key
Step 6: Configuring SSL Enabled Virtual Hosts
SSLEngine on
SSLCertificateFile /usr/local/apache/conf/ssl.crt/server.crt
SSLCertificateKeyFile /usr/local/apache/conf/ssl.key/server.key
SetEnvIf User-Agent ".*MSIE.*" nokeepalive ssl-unclean-shutdown
CustomLog logs/ssl_request_log \
"%t %h %{SSL_PROTOCOL}x %{SSL_CIPHER}x \"%r\" %b"
Step 7: Restart Apache and Test
/etc/init.d/httpd stop
/etc/init.d/httpd stop
https://public.akadia.com
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