Instantly share code, notes, and snippets.

Embed
What would you like to do?
Self Signed Certificate with Custom Root CA

Create Root CA (Done once)

Create Root Key

Attention: this is the key used to sign the certificate requests, anyone holding this can sign certificates on your behalf. So keep it in a safe place!

openssl genrsa -des3 -out rootCA.key 4096

If you want a non password protected key just remove the -des3 option

Create and self sign the Root Certificate

openssl req -x509 -new -nodes -key rootCA.key -sha256 -days 1024 -out rootCA.crt

Here we used our root key to create the root certificate that needs to be distributed in all the computers that have to trust us.

Create a certificate (Done for each server)

This procedure needs to be followed for each server/appliance that needs a trusted certificate from our CA

Create the certificate key

openssl genrsa -out mydomain.com.key 2048

Create the signing (csr)

The certificate signing request is where you specify the details for the certificate you want to generate. This request will be processed by the owner of the Root key (you in this case since you create it earlier) to generate the certificate.

Important: Please mind that while creating the signign request is important to specify the Common Name providing the IP address or domain name for the service, otherwise the certificate cannot be verified.

I will describe here two ways to gener

Method A (Interactive)

If you generate the csr in this way, openssl will ask you questions about the certificate to generate like the organization details and the Common Name (CN) that is the web address you are creating the certificate for, e.g mydomain.com.

openssl req -new -key mydomain.com.key -out mydomain.com.csr

Method B (One Liner)

This method generates the same output as Method A but it's suitable for use in your automation :) .

openssl req -new -sha256 -key mydomain.com.key -subj "/C=US/ST=CA/O=MyOrg, Inc./CN=mydomain.com" -out mydomain.com.csr

If you need to pass additional config you can use the -config parameter, here for example I want to add alternative names to my certificate.

openssl req -new -sha256 \
    -key mydomain.com.key \
    -subj "/C=US/ST=CA/O=MyOrg, Inc./CN=mydomain.com" \
    -reqexts SAN \
    -config <(cat /etc/ssl/openssl.cnf \
        <(printf "\n[SAN]\nsubjectAltName=DNS:mydomain.com,DNS:www.mydomain.com")) \
    -out mydomain.com.csr

Verify the csr's content

openssl req -in mydomain.com.csr -noout -text

Generate the certificate using the mydomain csr and key along with the CA Root key

openssl x509 -req -in mydomain.com.csr -CA rootCA.crt -CAkey rootCA.key -CAcreateserial -out mydomain.com.crt -days 500 -sha256

Verify the certificate's content

openssl x509 -in mydomain.com.crt -text -noout
@dthrash

This comment has been minimized.

dthrash commented Mar 1, 2018

How does the private key fit in here? Doesn't the pem file need to be generated too?

@fxpires

This comment has been minimized.

fxpires commented Mar 6, 2018

The files with ".key" extension are the private keys.

@qfan

This comment has been minimized.

qfan commented Apr 23, 2018

Is there a way to inform openssl to ask for the SAN (Subject Alternative Name) when generating the CSR?

@kalloa

This comment has been minimized.

kalloa commented May 12, 2018

@qfan You can use -config option to pass SAN to openssl
openssl req -new -key mydomain.com.key -out mydomain.com.csr -config certificate.conf
this is an example of certificate.conf

[req]
default_bits = 2048
prompt = no
default_md = sha256
req_extensions = req_ext
distinguished_name = dn
[dn]
C = HU
ST = Budapest
L = Budapest
O = ACME
OU = ACME Inc
emailAddress = kalloa@example.com
CN = example.com
[req_ext]
subjectAltName = @alt_names
[alt_names]
DNS.1 = example.com

@jkpaye

This comment has been minimized.

jkpaye commented May 31, 2018

Suggest you change the encryption from triple des to something stronger.

@scipilot

This comment has been minimized.

scipilot commented Jun 11, 2018

@qfan You will also need to pass the same config to the x509 command when you use the CSR, with -extfile certificate.conf -extensions req_ext. Took me a while to figure out.

@Fermec28

This comment has been minimized.

Fermec28 commented Jun 25, 2018

can I Generate the certificate using the third-domain csr and key along with the CA mydomain key ?
Root
mydomain
third-domain

@vs4vijay

This comment has been minimized.

vs4vijay commented Oct 10, 2018

Whats the difference between these two lines:

openssl x509 -req -in localhost.csr -CA root-CA.crt -CAkey root-CA.pem -CAcreateserial -out localhost.crt -days 365 -sha256

AND

openssl x509 -req -in localhost.csr -signkey root-CA.pem -out localhost.crt -days 365 -sha256

Are these commands are same? I have checked the output from these... Output were different but I guess both are used for signing CSR with Root CA... but whats the difference?

@choas75

This comment has been minimized.

choas75 commented Oct 25, 2018

@qfan You will also need to pass the same config to the x509 command when you use the CSR, with -extfile certificate.conf -extensions req_ext. Took me a while to figure out.

This is actually a very important comment. If forgotten the subjectAltName with the IP address will be missing!
Thanks scipilot!

@anandpathaksharma

This comment has been minimized.

anandpathaksharma commented Nov 2, 2018

@fntlnz - thank you very, very much for this Gist, it has enabled me to FINALLY get past a major hurdle with app development on Android Google Chrome!!!

I wanted to ask if you could perhaps update the gist to reflect the addition of "Subject Alternative Name" as the Common Name has become (according to some SO answers I've seen) a non-authoritative representation of the domain name and, apparently, will be phased out in some time. It has become important (and modern Firefox and Chrome at least demand it) that certificates be generated specifying DNS entries representing the domain name using the subjectAltName config setting. Source: https://stackoverflow.com/a/49087278.

Having learned this, I can say that almost all the steps in this Gist work for Google Chrome but, without some adjustments, Chrome keeps displaying an SSL Invalid message (and more importantly, in chromeless web apps, displaying an HTTPS Error warning bar at the top). In order to pass all the checks so that Chrome doesn't show this warning bar in chromeless apps, you need to specify the subjectAltName values for your domain(s), e.g. example.com and www.example.com.

Using the technique mentioned by @scipilot is what cleared all this up. @scipilot's comment was in response to @qfan's question:

@qfan You will also need to pass the same config to the x509 command when you use the CSR, with -extfile certificate.conf -extensions req_ext. Took me a while to figure out.

@scipilot - thank you SO MUCH for returning and sharing this information (as @choas75 already mentioned).

@fntlnz, I'd like to suggest that you modify your instructions for the section:

If you need to pass additional config you can use the -config parameter, here for example I want to add alternative names to my certificate.

To include the instructions provided by @scipilot. I feel it will save A LOT of people A LOT of head scratching!

Thanks everyone! 😄 👍

@nuvitu

This comment has been minimized.

nuvitu commented Nov 22, 2018

After did all steps, When I put .cer file to ios, it is shown that Not verified (Unverified profile - The authenticity of "xxx" cannot be verified.) => So I can install it, but after installed, it is still not verified.

Could you please tell me why ?

Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment