markdown 如何生成SSL CSR或自签名SSL证书

Posted 2021-05-06

# How to generate an SSL CSR or self signed SSL certificate

## 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 2048
    
    Generating RSA private key, 2048 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.example.com, then enter public.example.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]:Example
    Organizational Unit Name (eg, section) []:Information Technology
    Common Name (eg, your name or your server's hostname) []:public.example.com
    Email Address []:martin dot zahn at example dot ch
    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=Example/OU=Information
    Technology/CN=public.example.com/Email=martin dot zahn at example dot ch
    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 on Apache

    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.example.com