How to create a self-signed certificate with OpenS

Question

I'm adding HTTPS support to an embedded Linux device. I have tried to generate a self-signed certificate with these steps:

openssl req -new > cert.csr
openssl rsa -in privkey.pem -out key.pem
openssl x509 -in cert.csr -out cert.pem -req -signkey key.pem -days 1001
cat key.pem>>cert.pem

This works, but I get some errors with, for example, Google Chrome:

This is probably not the site you are looking for!
The site's security certificate is not trusted!

Am I missing something? Is this the correct way to build a self-signed certificate?

Answer 1

One-liner version 2017:

CentOS:

openssl req -x509 -nodes -sha256 -newkey rsa:2048 \
-keyout localhost.key -out localhost.crt \
-days 3650 \
-subj "CN=localhost" \
-reqexts SAN -extensions SAN \
-config <(cat /etc/pki/tls/openssl.cnf <(printf "\n[SAN]\nsubjectAltName=IP:127.0.0.1,DNS:localhost"))

Ubuntu:

openssl req -x509 -nodes -sha256 -newkey rsa:2048 \
-keyout localhost.key -out localhost.crt \
-days 3650 \
-subj "CN=localhost" \
-reqexts SAN -extensions SAN \
-config <(cat /etc/ssl/openssl.cnf <(printf "\n[SAN]\nsubjectAltName=IP:127.0.0.1,DNS:localhost"))

Answer 2

You can do that in one command:

openssl req -x509 -newkey rsa:4096 -keyout key.pem -out cert.pem -days 365

You can also add -nodes (short for no DES) if you don't want to protect your private key with a passphrase. Otherwise it will prompt you for "at least a 4 character" password.

The days parameter (365) you can replace with any number to affect the expiration date. It will then prompt you for things like "Country Name", but you can just hit Enter and accept the defaults.

Add -subj '/CN=localhost' to suppress questions about the contents of the certificate (replace localhost with your desired domain).

Self-signed certificates are not validated with any third party unless you import them to the browsers previously. If you need more security, you should use a certificate signed by a certificate authority (CA).

Answer 3

Here are the options described in @diegows's answer, described in more detail, from the documentation:

openssl req -x509 -newkey rsa:2048 -keyout key.pem -out cert.pem -days XXX

req

PKCS#10 certificate request and certificate generating utility.

-x509

this option outputs a self signed certificate instead of a certificate request. This is typically used to generate a test certificate or a self signed root CA.

-newkey arg

this option creates a new certificate request and a new private key. The argument takes one of several forms. rsa:nbits, where nbits is the number of bits, generates an RSA key nbits in size.

-keyout filename

this gives the filename to write the newly created private key to.

-out filename

This specifies the output filename to write to or standard output by default.

-days n

when the -x509 option is being used this specifies the number of days to certify the certificate for. The default is 30 days.

-nodes

if this option is specified then if a private key is created it will not be encrypted.

The documentation is actually more detailed than the above; I just summarized it here.

Answer 4

Generate keys

I am using /etc/mysql for cert storage because /etc/apparmor.d/usr.sbin.mysqld contains /etc/mysql/*.pem r.

sudo su -
cd /etc/mysql
openssl genrsa -out ca-key.pem 2048;
openssl req -new -x509 -nodes -days 1000 -key ca-key.pem -out ca-cert.pem;
openssl req -newkey rsa:2048 -days 1000 -nodes -keyout server-key.pem -out server-req.pem;
openssl x509 -req -in server-req.pem -days 1000 -CA ca-cert.pem -CAkey ca-key.pem -set_serial 01 -out server-cert.pem;
openssl req -newkey rsa:2048 -days 1000 -nodes -keyout client-key.pem -out client-req.pem;
openssl x509 -req -in client-req.pem -days 1000 -CA ca-cert.pem -CAkey ca-key.pem -set_serial 01 -out client-cert.pem;

Add configuration

/etc/mysql/my.cnf

[client]
ssl-ca=/etc/mysql/ca-cert.pem
ssl-cert=/etc/mysql/client-cert.pem
ssl-key=/etc/mysql/client-key.pem

[mysqld]
ssl-ca=/etc/mysql/ca-cert.pem
ssl-cert=/etc/mysql/server-cert.pem
ssl-key=/etc/mysql/server-key.pem

On my setup, Ubuntu server logged to: /var/log/mysql/error.log

Follow up notes:

• SSL error: Unable to get certificate from '...'

  MySQL might be denied read access to your certificate file if it is not in apparmors configuration. As mentioned in the previous steps^, save all our certificates as .pem files in the /etc/mysql/ directory which is approved by default by apparmor (or modify your apparmor/SELinux to allow access to wherever you stored them.)

• SSL error: Unable to get private key

  Your MySQL server version may not support the default rsa:2048 format

  Convert generated rsa:2048 to plain rsa with:

  openssl rsa -in server-key.pem -out server-key.pem
  openssl rsa -in client-key.pem -out client-key.pem
  

• Check if local server supports SSL:

  mysql -u root -p
  mysql> show variables like "%ssl%";
  +---------------+----------------------------+
  | Variable_name | Value                      |
  +---------------+----------------------------+
  | have_openssl  | YES                        |
  | have_ssl      | YES                        |
  | ssl_ca        | /etc/mysql/ca-cert.pem     |
  | ssl_capath    |                            |
  | ssl_cert      | /etc/mysql/server-cert.pem |
  | ssl_cipher    |                            |
  | ssl_key       | /etc/mysql/server-key.pem  |
  +---------------+----------------------------+
  

• Verifying a connection to the database is SSL encrypted:

  Verifying connection

  When logged in to the MySQL instance, you can issue the query:

  show status like 'Ssl_cipher';
  

  If your connection is not encrypted, the result will be blank:

  mysql> show status like 'Ssl_cipher';
  +---------------+-------+
  | Variable_name | Value |
  +---------------+-------+
  | Ssl_cipher    |       |
  +---------------+-------+
  1 row in set (0.00 sec)
  

  Otherwise, it would show a non-zero length string for the cypher in use:

  mysql> show status like 'Ssl_cipher';
  +---------------+--------------------+
  | Variable_name | Value              |
  +---------------+--------------------+
  | Ssl_cipher    | DHE-RSA-AES256-SHA |
  +---------------+--------------------+
  1 row in set (0.00 sec)
  

• Require ssl for specific user's connection ('require ssl'):

  • SSL

  Tells the server to permit only SSL-encrypted connections for the account.

  GRANT ALL PRIVILEGES ON test.* TO 'root'@'localhost'
    REQUIRE SSL;
  

  To connect, the client must specify the --ssl-ca option to authenticate the server certificate, and may additionally specify the --ssl-key and --ssl-cert options. If neither --ssl-ca option nor --ssl-capath option is specified, the client does not authenticate the server certificate.

---

Alternate link: Lengthy tutorial in Secure PHP Connections to MySQL with SSL.

Answer 5

You have the general procedure correct. The syntax for the command is below.

openssl req -new -key {private key file} -out {output file}

However, the warnings are displayed, because the browser was not able to verify the identify by validating the certificate with a known Certificate Authority (CA).

As this is a self-signed certificate there is no CA and you can safely ignore the warning and proceed. Should you want to get a real certificate that will be recognizable by anyone on the public Internet then the procedure is below.

1. Generate a private key
2. Use that private key to create a CSR file
3. Submit CSR to CA (Verisign or others, etc.)
4. Install received cert from CA on web server
5. Add other certs to authentication chain depending on the type cert

I have more details about this in a post at Securing the Connection: Creating a Security Certificate with OpenSSL

Answer 6

As of 2018, the following command serves all your needs, including SAN:

openssl req -x509 -newkey rsa:4096 -sha256 -days 3650 -nodes -keyout example.key -out example.crt -extensions san -config <(echo "[req]"; echo distinguished_name=req; echo "[san]"; echo subjectAltName=DNS:example.com,DNS:example.net,IP:10.0.0.1) -subj /CN=example.com

In OpenSSL ≥ 1.1.1, this can be shortened to:

openssl req -x509 -newkey rsa:4096 -sha256 -days 3650 -nodes -keyout example.key -out example.crt -subj /CN=example.com -addext subjectAltName=DNS:example.com,DNS:example.net,IP:10.0.0.1

It creates a certificate that is

• valid for the domains example.com and example.net (SAN),
• also valid for the IP address 10.0.0.1 (SAN),
• relatively strong (as of 2018) and
• valid for 3650 days (~10 years).

It creates the following files:

• Private key: example.key
• Certificate: example.crt

All information is provided at the command line. There is no annoying interactive input. There is no messing around with config files. All necessary steps are executed by this single OpenSSL invocation: from private key generation up to the self-signed certificate.

Since the certificate is self-signed and needs to be accepted by users manually, it doesn't make sense to use a short expiration or weak cryptography.

In the future, you might want to use more than 4096 bits for the RSA key and a hash algorithm stronger than sha256, but as of 2018 these are sane values. They are sufficiently strong while being supported by all modern browsers.

Remark #1: Parameter "nodes"

Theoretically you could leave out the -nodes parameter (which means "no DES encryption"), in which case example.key would be encrypted with a password. However, this is almost never useful for a server installation, because you would either have to store the password on the server as well, or you'd have to enter it manually on each reboot.

Remark #2: MinGW

On Windows / MinGW, you should prefix the command with MSYS_NO_PATHCONV=1:

MSYS_NO_PATHCONV=1 openssl ...

Alternatively, run the command in the plain cmd.exe Windows command prompt.

Remark #3: See also

• Provide subjectAltName to OpenSSL directly on the command line
• How do I add multiple email addresses to an SSL certificate via the command line?
• More information about MSYS_NO_PATHCONV