Generate and import a Self-Signed SSL certificate on Mac OS X Sierra

Step 1: Verify that you have openssl installed.

$ which openssl
/usr/bin/openssl
$

If not, install openssl using:

$ brew install openssl
$

If you are using Microsoft(r) Windows, checkout http://gnuwin32.sourceforge.net/packages/openssl.htm for details about the openssl package on Windows.

If you using Linux, you can use the default package manager to get the openssl package installed on your box. For example:

# In case of Ubuntu:
$ sudo apt-get install openssl
$

Step 2: Create a RSA private key.

# The below command will create a file named 'server.pass.key' and place it in the same folder where the command is executed. 
$ openssl genrsa -des3 -passout pass:x -out server.pass.key 2048

# The below command will use the 'server.pass.key' file that just generated and create 'server.key'.
$ openssl rsa -passin pass:x -in server.pass.key -out server.key

# We no longer need the 'server.pass.key'
$ rm server.pass.key
$

server.key is a PEM RSA private key. To know more about what is a PEM file and it’s significance, read What is a Pem file and how does it differ from other OpenSSL Generated Key File Formats? at serverfault.com.

Step 3: Create the Certificate Signing Request (CSR) utilizing the RSA private key we generated in the last step.

# The below command will ask you for information that would be included in the certificate. Since this is a self-signed certificate, there is no need to provide the 'challenge password' (to leave it blank, press enter).
$ openssl req -new -key server.key -out server.csr
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]:
State or Province Name (full name) [Some-State]:
Locality Name (eg, city) []:
Organization Name (eg, company) [Internet Widgits Pty Ltd]:
Organizational Unit Name (eg, section) []:
Common Name (e.g. server FQDN or YOUR name) []: <provide a CN - usually, FQDN of your site>
Email Address []: <provide the email address to be included in the certificate signing request>

Please enter the following 'extra' attributes
to be sent with your certificate request
A challenge password []:
An optional company name []:
$

The ‘challenge password’ is used by the Certificate Authority (CA) to authenticate the certificate owner when they have to revoke the certificate. There is no way to revoke a Self-Signed Certificate via Certificate Revocation List (CRL) (refer: https://devcenter.heroku.com/articles/ssl-certificate-self#generate-private-key-and-certificate-signing-request]

As a result of executing the above command, you will find a file named server.csr (‘csr’ stands for Certificate Signing Request) in the same directory.

Step 4: Generate a file named, v3.ext with the below listed contents:

$ cat v3.ext
authorityKeyIdentifier=keyid,issuer
basicConstraints=CA:FALSE
keyUsage = digitalSignature, nonRepudiation, keyEncipherment, dataEncipherment
subjectAltName = @alt_names

[alt_names]
DNS.1 = <specify-the-same-common-name-that-you-used-while-generating-csr-in-the-last-step>
$

This step is required because when you load the certificate in the Chrome browser, it would display an error portrayed in the below screenshot.

Setting the DNS.1 value in v3.ext file to be same as the Common Name that you mentioned while generating the certificate signing request would resolve the error. Refer https://stackoverflow.com/questions/43665243/chrome-invalid-self-signed-ssl-cert-subject-alternative-name-missing for more details about the subject alternate name missing error and the solution.

1. Create the SSL Certificate utilizing the CSR created in the last step.

   $ openssl x509 -req -sha256 -extfile v3.ext -days 365 -in server.csr -signkey server.key -out server.crt
   Signature ok
   subject=/C=<country>/ST=<state>/L=<locality>/O=<organization-name>/OU=<organization-unit-name>/CN=<common-name-probably-server-fqdn>/emailAddress=<email-address-provided-while-generating-csr>
   Getting Private key
   $
   

The above command will use the Certificate Signing Request and the RSA Private Key that we generated as part of executing the previous steps and generate a Certificate file named, server.crt (‘crt’ is an abbreviation of ‘Certificate’) and place it in the same directory.

Step 5: Import the newly generated certificate in your Keychain (Mac OSX only).

Since this is a self-signed certificate, the browser would display a warning mentioning that the certificate is self-signed and the website should not be trusted as portrayed in the below-listed screenshot captured on the Chrome browser.

Click the Advanced hyperlink at the bottom of the warning page and click Proceed to hyperlink.

The browser will allow you to proceed and open the homepage but will mark the site as Not-Secure as portrayed in the image below.

To avoid this accepting the self-signed certificate everytime you restart chrome or restart your web server, follow the steps outlined at Google Chrome, Mac OS X and Self-Signed SSL Certificates to add the certificate to your Mac OSX Keychain. Restart Chrome.

Other platforms like Microsoft(r) Windows and Linux have similar techniques to import a certificate into a browser. A quick Google(r) search should be able to provide you with the exact steps based on the browser that you use.

Now Chrome should happily display the green ‘Secure’ icon against the URL when you navigate to your locally deployed website. Also, the Security tab within the Developer Tools should list the site as ‘Secure’ as portrayed in the screenshot below.

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References:

1. Generating a self-signed certificate using OpenSSL
2. How to create a self-signed certificate with openssl?
3. Creating a Self-Signed SSL Certificate
4. What is a Pem file and how does it differ from other OpenSSL Generated Key File Formats?
5. Chrome: Invalid self signed SSL cert – “Subject Alternative Name Missing”
6. Google Chrome, Mac OS X and Self-Signed SSL Certificates

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