This is a text-only version of the following page on https://raymii.org:

This is a text-only version of the following page on https://raymii.org:
---
Title : OpenSSL generate self signed certificate with SAN in one command (subject alternative name)
Author : Remy van Elst
Date : 14-10-2022 22:02
URL : https://raymii.org/s/tutorials/OpenSSL_generate_self_signed_cert_with_Subject_Alternative_name_oneliner.html
Format : Markdown/HTML
---

This small one liner lets you generate an OpenSSL self signed certificate with both a common name and a [Subject Alternative Name (SAN)](https://en.wikipedia.org/wiki/Subject_Alternative_Name). Most guides online require you to specify a separate config file but this guide uses a bash trick [(process substitution)](https://web.archive.org/web/20221014191420/https://superuser.com/questions/1059781/what-exactly-is-in-bash-and-in-zsh) to pass such a config file to OpenSSL via the command line. If you are using OpenSSL 1.1.1 or higher, there now finally is a built in command line option which I'll also cover.

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The reason for such a one liner is that I was playing around with a docker
registry web GUI that complained that my self signed certificate used an old
style CN (common name) and not the SAN field. It appeared to be an underlying
Go warning. So I had to regenerate my self signed certificate with a
[Subject Alternative Name][6] next to a common name. Since I was toying
around, I didn't want to save a bunch of unrelated config files. Just make me
a sandwich, err, certificate.

I often write about OpenSSL. [You can see all my OpenSSL articles here][2]. I've
also made a convenient [OpenSSL command generator][3] which generates a command
for you to execute whenever you need a certificate.

### Generate Self Signed Certificate with SAN

If you are using [OpenSSL 1.1.1 or higher][5] you can simply use the
`-addext "subjectAltName = ` parameter like so:

openssl req -nodes -x509 -sha256 -newkey rsa:4096 \
-keyout example.org.key \
-out example.org.crt \
-days 356 \
-subj "/C=NL/ST=Zuid Holland/L=Rotterdam/O=ACME Corp/OU=IT Dept/CN=example.org" \
-addext "subjectAltName = DNS:localhost,DNS:example.org"

Replace `example.org` with your domain name. If you use an IP address, prefix
it with `IP:` instead of `DNS:`.

If you use an older version of OpenSSL, you can use [bash process
substitution][4] to provide an OpenSSL config file directly without saving
that file anywhere:

openssl req -nodes -x509 -sha256 -newkey rsa:4096 \
-keyout example.org.key \
-out example.org.crt \
-days 356 \
-subj "/C=NL/ST=Zuid Holland/L=Rotterdam/O=ACME Corp/OU=IT Dept/CN=example.org" \
-extensions san \
-config <( \
echo '[req]'; \
echo 'distinguished_name=req'; \
echo '[san]'; \
echo 'subjectAltName=DNS:localhost,DNS:example.org')

In the last line, do not forget to add 'DNS:' in front of your hostname. Otherwise you
will receive a vague error message regarding the SAN extension not being found.

[2]: /s/tags/openssl.html
[3]: /s/software/OpenSSL_Command_Generator.html
[4]: https://web.archive.org/web/20221014191420/https://superuser.com/questions/1059781/what-exactly-is-in-bash-and-in-zsh
[5]: https://web.archive.org/web/20221014193739/https://github.com/openssl/openssl/commit/bfa470a4f64313651a35571883e235d3335054eb
[6]: https://en.wikipedia.org/wiki/Subject_Alternative_Name

---

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