HOWTO: Create Your Own Self-Signed Certificate with Subject Alternative Names Using OpenSSL in Ubuntu Bash for Window
My main development workstation is a Windows 10 machine, so we'll approach this from that viewpoint.
Recently, Google Chrome started giving me a warning when I open a site that uses https and self-signed certificate on my local development machine due to some SSL certificate issues like the one below:
or one that is described in this forum post which I originally got.
I made my self-signed certificate using MAKECERT utility previously. Apparently, this tool does not support creating self-signed SSL certificate with Subject Alternative Name (SAN). If anyone knows different, please let me know.
So, after doing some searches, it seems that OpenSSL is the best solution for this.
If you are trying to use OpenSSL on Windows like me, you will probably be scratching your head on where to start. Build from the repository? Ouch. That's what they called yak shaving. I just want to quickly create my own damn self-signed certificate, not build a factory that can do that. Sure, there is binary installation available here, but after getting it installed and trying to figure out how to make it run nicely with PowerShell, I gave up.
Luckily, Windows 10 now has the ability to run Ubuntu Bash and after playing around with it, this seems to be the best way forward when using openssl
.
To set it up, follow the instruction here.
To install openssl
run the following command from the bash shell:
sudo apt-get install openssl
Once installed, you are ready to create your own self-signed certificate.
I am using this OpenSSL Ubuntu article as the base, but there are some modifications along the way, so I'll just explain the way I did it here. If you need further information, please visit that article.
The original article is using SHA1 but we really need to move to something else that is stronger like SHA256. If you are using SHA1 as suggested, you will be getting the Your connection is not private page in Chrome.
We will use your user profile root directory (~/
which points to /home/jchandra
in my case) to do this work. If you use anything else, you might need to customize the caconfig.cnf
and localhost.cnf
content below.
To create your environment, run the following in bash:
cd ~/ && mkdir myCA && mkdir -p myCA/signedcerts && mkdir myCA/private && cd myCA
This will create the following directories under your user profile root folder:
Directory | Contents |
---|---|
~/myCA |
contains CA certificate, certificates database, generated certificates, keys, and requests |
~/myCA/signedcerts |
contains copies of each signed certificate |
~/myCA/private |
contains the private key |
To create the database, enter the following in bash:
echo '01' > serial && touch index.txt
Create caconfig.cnf
using vim
or nano
or whatever Linux text-editor of your choice.
To create it using vim
, do the following:
vim ~/myCA/caconfig.cnf
To create it using nano
do the following:
nano ~/myCA/caconfig.cnf
The content should be like so:
# My sample caconfig.cnf file.
#
# Default configuration to use when one is not provided on the command line.
#
[ ca ]
default_ca = local_ca
#
#
# Default location of directories and files needed to generate certificates.
#
[ local_ca ]
dir = /home/jchandra/myCA
certificate = $dir/cacert.pem
database = $dir/index.txt
new_certs_dir = $dir/signedcerts
private_key = $dir/private/cakey.pem
serial = $dir/serial
#
#
# Default expiration and encryption policies for certificates
#
default_crl_days = 365
default_days = 1825
# sha1 is no longer recommended, we will be using sha256
default_md = sha256
#
policy = local_ca_policy
x509_extensions = local_ca_extensions
#
#
# Copy extensions specified in the certificate request
#
copy_extensions = copy
#
#
# Default policy to use when generating server certificates.
# The following fields must be defined in the server certificate.
#
# DO NOT CHANGE "supplied" BELOW TO ANYTHING ELSE.
# It is the correct content.
#
[ local_ca_policy ]
commonName = supplied
stateOrProvinceName = supplied
countryName = supplied
emailAddress = supplied
organizationName = supplied
organizationalUnitName = supplied
#
#
# x509 extensions to use when generating server certificates
#
[ local_ca_extensions ]
basicConstraints = CA:false
#
#
# The default root certificate generation policy
#
[ req ]
default_bits = 2048
default_keyfile = /home/jchandra/myCA/private/cakey.pem
#
# sha1 is no longer recommended, we will be using sha256
default_md = sha256
#
prompt = no
distinguished_name = root_ca_distinguished_name
x509_extensions = root_ca_extensions
#
#
# Root Certificate Authority distinguished name
#
# DO CHANGE THE CONTENT OF THESE FIELDS TO MATCH
# YOUR OWN SETTINGS!
#
[ root_ca_distinguished_name ]
commonName = InvoiceSmashDev Root Certificate Authority
stateOrProvinceName = NSW
countryName = AU
emailAddress = support.team@blahblahblah.com
organizationName = Coupa InvoiceSmash
organizationalUnitName = Development
#
[ root_ca_extensions ]
basicConstraints = CA:true
- In
[ local_ca ]
section, make sure you replace<username>
with your Ubuntu username that you created when you setup Ubuntu on Windows 10. Mine for example isdir = /home/jchandra/myCA
. NOTE: DO NOT USE~/myCA
. It does not work..
Similarly, change thedefault_keyfile
setting in[ req ]
section to be the same. - Leave the
[ local_ca_policy ]
section alone.commonName = supplied
, etc. are correct and not to be overwritten. - In
[ root_ca_distinguished_name ]
section, replace all values to your own settings.
- Run the following command so
openssl
will pick the settings automatically:
export OPENSSL_CONF=~/myCA/caconfig.cnf
- Generate the Certificate Authority (CA) certificate:
openssl req -x509 -newkey rsa:2048 -out cacert.pem -outform PEM -days 1825
- Enter and retype the password you wish to use to import/export the certificate.
NOTE: Remember this password, you will need it throughout this walk-through.
Once you are done you should have the following files:
File | Content |
---|---|
~/myCA/cacert.pem |
CA public certificate |
~/myCA/private/cakey.pem |
CA private key |
In Windows, we will be using .crt
file instead, so create one using the following command:
openssl x509 -in cacert.pem -out cacert.crt
Now that you have your CA, you can create the actual self-signed SSL certificate.
But first, we need to create the configuration file for it. So again, use vim
or nano
, etc. to create the file. In this example, I will call mine localhost.cnf
since that's the server that I am going to be using to test my development code. You can call it whatever you want. Just make sure you use the right filename in the export
command later on.
Below is the content of ~/myCA/localhost.cnf
:
#
# localhost.cnf
#
[ req ]
prompt = no
distinguished_name = server_distinguished_name
req_extensions = v3_req
[ server_distinguished_name ]
commonName = localhost
stateOrProvinceName = NSW
countryName = AU
emailAddress = invoicesmashteam@coupa.com
organizationName = Coupa InvoiceSmash
organizationalUnitName = Development
[ v3_req ]
basicConstraints = CA:FALSE
keyUsage = nonRepudiation, digitalSignature, keyEncipherment
subjectAltName = @alt_names
[ alt_names ]
DNS.0 = localhost
DNS.1 = invoicesmash.local
- Change the values in
[ server_distinguished_name ]
section to match your own settings. - In
[ alt_names ]
section, change the value forDNS.0
andDNS.1
to whatever you need. In my case, I test my web application usinghttps://localhost:44300
, therefore the correct value for me isDNS.0 = localhost
. I am not sure what to do withDNS.1
so, I just changed it toDNS.1 = invoicesmash.local
. If so happen that I have a host entry in myhosts
file that matches this (mapped to IP Address127.0.0.1
), it should still work.
Once you created the configuration file, you need to export it:
export OPENSSL_CONF=~/myCA/localhost.cnf
Now generate the certificate and key:
openssl req -newkey rsa:2048 -keyout tempkey.pem -keyform PEM -out tempreq.pem -outform PEM
Again, provide the password that you previously entered and wait for the command complete.
Next, run the following to create the unencrypted key file:
openssl rsa < tempkey.pem > server_key.pem
Again, provide the password that you previously entered and wait for the command to be completed.
Now switch back the export to caconfig.cnf
so we can sign the new certificate request with the CA:
export OPENSSL_CONF=~/myCA/caconfig.cnf
And sign it:
openssl ca -in tempreq.pem -out server_crt.pem
Again, provide the password that you previously entered and wait for the command to be completed and just type in Y whenever it asks you for [y/n]
.
Now you should have your self-signed certificate and the key.
File | Content |
---|---|
~/myCA/server_crt.pem |
Self signed SSL certificate |
~/myCA/server_key.pem |
Self signed SSL certificate private key |
In Windows, we mostly use .pfx
and .crt
files. Therefore, we need to convert the .pem
file to .pfx
. We'll use cat
to combine server_key.pem
and server_crt.pem
into a file called hold.pem
. Then we will do the conversion using openssl pkcs12
command as shown below. You can use whatever text you want to describe your new .pfx
file in the -name
parameter.
cat server_key.pem server_crt.pem > hold.pem
openssl pkcs12 -export -out localhost.pfx -in hold.pem -name "InvoiceSmash Dev Self-Signed SSL Certificate"
Again, provide the password that you previously entered and wait for the command to be completed.
Now you should have the following files that we will use in the next section.
File | Content |
---|---|
~/myCA/localhost.pfx |
Self signed SSL certificate in PKCS#12 format |
~/myCA/cacert.crt |
CA certificate used to signed the self-signed certificate |
It seems it is forbidden to touch the Linux Subsystem from Windows side, but you can touch Windows side from Linux side, so that's what we are going to do.
To copy the files from inside Ubuntu, you need to know where you want to copy the files to on Windows side. For example, if I want to copy the files to C:\certificates
folder, I'd do something like cp {localhost.pfx,cacert.crt} /mnt/c/certificates
.
See this faq if you want to know more about this.
To install the CA and self-signed certificates, all you need to do is double-click the file from where you copied them into.
Once clicked, just follow the Install Certificate steps and you should be good.
For the CA Certificate (`cacert.crt), make sure you install it to Local Machine, Trusted Root Certification Authorities.
For the self-signed certificate (localhost.pfx
), install it to Local Machine, enter the password as previously, and store it in Personal.
That's it. Now you can configure your application to use the new certificate. In my situation, I just need to configure the Azure Cloud Service project to use that certificate as pointed by this document. I do not know your workflow, so it might be different.
Instead of exporting you could just use
-config caconfig.cnf
. Also, addingencrypt_key = no
to[ req ]
makes life easier.