Creating SSL keys, CSRs, self-signed certificates, and .pem files.

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 What is the whole darned process?

Well that’s a good question. For my purposes, this is what I need to know:

1. Create a Private Key. These usually end in the file extension “key” If you already have one, don’t worry - it’s cool, we’ll be using that one.
2. Create a Certificate Signing Request. These usually end in the extension “csr”, and are sent to the certificate authority to generate a certificate.
3. If you’re not going to be using an existing service (usually for pay) as a certificate authority, you can create your own Certificate Authority, or self-sign your certificate.
4. Submit your CSR to the CA and get the results. If you’re doing it yourself, I’ll tell you how. The CA creates a Certificate file, which ends in “.crt”.
5. Take the whole collection of files, keep them somewhere safe, and mash them together to create your PEM file (this is usually just used for email.)

So. Let’s get started, eh?

Step Zero: Basic Assumptions

• I’ll assume your domain name is domain.tld.
• I’ll assume you have OpenSSL installed.
• I’ll assume that you are running some form of Linux. I use Debian.

Step One: Create your Private Key

Ok, here you’re going to create your key - and treat is as such. This should be kept private, and not shared with anyone.

Now, you have a couple of options here - the first is to create your private key with a password, the other is to make it without one. If you create it with a password, you have to type it in every time your start any server that uses it.

Important: If you create your private key with a password, you can remove it later. I recommend creating your private key with a password, and then removing it temporarily every time you need to use it. When you’re done with the key without a password, delete it so it isn’t a security risk.

Create your Private key  with a password

openssl genrsa -des3 -out domain.tld.encrypted.key 1024

Create your Private key  without a password

openssl genrsa -out domain.tld.key 1024

If you created your private key with a password, you’ll want to complete the rest of the steps using a decrypted private key - else you’ll have to type in your password every time you use the certificate (ie: every time you start a daemon using that certificate.)

Remove the password and encryption from your private key

openssl rsa -in domain.tld.encrypted.key -out domain.tld.key

Step Two: Create a CSR

On this step you’re going to create what you actually send to your Certificate Authority. If you set a password with your Private Key, you’ll be required to enter it to create the CSR. After you finish all these steps, you can delete your CSR.

Create your Certificate Signing Request

openssl req -new -key domain.tld.key -out domain.tld.csr

Step Three: Create your Certificate

You have three options here: 1. Self-signing 2. Creating a certificate authority (CA) 3. Paying a CA to create your certificate for you.

Here’s what’s up: Self-signing is easy, free, and quick. Creating a CA isn’t terribly difficult, but probably more than you want to handle for something small. Paying for a CA can be cheap ($20), easy, quick, and comes with browser-recognition, which is generally important for public websites; especially commercial ones.

My advice: Self-sign your certificates for personal things, and pay for a certificate if its public and important.

If you’d like to pay for someone to sign your certificates, do some research and find which one you want to use. Next, find their instructions for submitting your CSR file.

Self-Sign your Certificate

openssl x509 -req -days 365 -in domain.tld.csr -signkey domain.tld.key -outdomain.tld.crt

If you do happen to want to setup your own certificate authority, check these resources out:

• http://www.g-loaded.eu/2005/11/10/be-your-own-ca/
• http://codeghar.wordpress.com/2008/03/17/create-a-certificate-authority-and-certificates-with-openssl/

Step Four: Creating a PEM file

A PEM file is used by many different daemons, however how to generate such a PEM file can be hard to come by. There are some complicated ways to build one, however I have had pretty good success with simply combining the .key and the .crt file together:

cat domain.tld.key domain.tld.crt > domain.tld.pem

Disclaimer

I am not an expert with SSL, which is exactly why I created this. This may not be accurate, YMMV, etc. Be careful. Also: Your .key is private. Keep that safe, with appropriate permissions. Make sure nobody else can access it, and do not give it away to anyone. If you have any insight, feel free to comment - I would appreciate them.

原帖地址：http://grahamc.com/blog/openssl-madness-how-to-create-keys-certificate-signing-requests-authorities-and-pem-files 

Creating SSL keys, CSRs, self-signed certificates, and .pem files.