Tutorial: Configure SSL/TLS on AL2023
Secure Sockets Layer/Transport Layer Security (SSL/TLS) creates an encrypted channel
between a web server and web client that protects data in transit from being eavesdropped
on. This tutorial explains how to add support manually for SSL/TLS on an EC2 instance with
AL2023 and Apache web server. This tutorial assumes that you are not using a load balancer.
If you are using Elastic Load Balancing, you can choose to configure SSL offload on the load balancer,
using a certificate from Amazon Certificate Manager
For historical reasons, web encryption is often referred to simply as SSL. While web
browsers still support SSL, its successor protocol TLS is less vulnerable to attack.
AL2023 disables server-side support for all versions of SSL by default. Security standards
bodies
This tutorial refers to modern web encryption simply as TLS.
Important
These procedures are intended for use with AL2023. If you are trying to set up an
EC2 instance running a different distribution, or an instance running an old version of
Amazon Linux, some procedures in this tutorial might not work. For
Ubuntu, see the following Ubuntu community documentation: Open SSL on
Ubuntu
Note
Alternatively, you can use Amazon Certificate Manager (ACM) for Amazon Nitro enclaves, which is an enclave application that allows you to use public and private SSL/TLS certificates with your web applications and servers running on Amazon EC2 instances with Amazon Nitro Enclaves. Nitro Enclaves is an Amazon EC2 capability that enables creation of isolated compute environments to protect and securely process highly sensitive data, such as SSL/TLS certificates and private keys.
ACM for Nitro Enclaves works with nginx running on your Amazon EC2 Linux instance to create private keys, to distribute certificates and private keys, and to manage certificate renewals.
To use ACM for Nitro Enclaves, you must use an enclave-enabled Linux instance.
For more information, see What is Amazon Nitro Enclaves? and Amazon Certificate Manager for Nitro Enclaves in the Amazon Nitro Enclaves User Guide.
Contents
Prerequisites
Before you begin this tutorial, complete the following steps:
-
Launch an EBS-backed AL2023 instance. For more information, see AL2023 on Amazon EC2.
-
Configure your security groups to allow your instance to accept connections on the following TCP ports:
-
SSH (port 22)
-
HTTP (port 80)
-
HTTPS (port 443)
For more information, see Authorize inbound traffic for your Linux instances in the Amazon EC2 User Guide.
-
-
Install the Apache web server. For step-by-step instructions, see Tutorial: Install a LAMP server on AL2023. Only the httpd package and its dependencies are needed, so you can ignore the instructions involving PHP and MariaDB.
-
To identify and authenticate websites, the TLS public key infrastructure (PKI) relies on the Domain Name System (DNS). To use your EC2 instance to host a public website, you need to register a domain name for your web server or transfer an existing domain name to your Amazon EC2 host. Numerous third-party domain registration and DNS hosting services are available for this, or you can use Amazon Route 53.
Step 1: Enable TLS on the server
This procedure takes you through the process of setting up TLS on AL2023 with a self-signed digital certificate.
Note
A self-signed certificate is acceptable for testing but not production. If you expose your self-signed certificate to the internet, visitors to your site are greeted by security warnings.
To enable TLS on a server
-
Connect to your instance and confirm that Apache is running. For more information, see Connecting to AL2023 instances.
[ec2-user ~]$
sudo systemctl is-enabled httpd
If the returned value is not "enabled," start Apache and set it to start each time the system boots.
[ec2-user ~]$
sudo systemctl start httpd && sudo systemctl enable httpd
-
To ensure that all of your software packages are up to date, perform a quick software update on your instance. This process may take a few minutes, but it is important to make sure that you have the latest security updates and bug fixes.
Note
The
-y
option installs the updates without asking for confirmation. If you would like to examine the updates before installing, you can omit this option.[ec2-user ~]$
sudo dnf install openssl mod_ssl
-
After you enter the following command, you will be taken to a prompt where you can enter information about your site.
[ec2-user ~]$
sudo openssl req -x509 -nodes -days 365 -newkey rsa:2048 -keyout /etc/pki/tls/private/apache-selfsigned.key -out /etc/pki/tls/certs/apache-selfsigned.crt
This generates a new file
apache-selfsigned.crt
in the/etc/pki/tls/certs/
directory. The specified file name matches the default that is assigned in the SSLCertificateFile directive in/etc/httpd/conf.d/ssl.conf
.Your instance now has the following files that you use to configure your secure server and create a certificate for testing:
-
/etc/httpd/conf.d/ssl.conf
The configuration file for mod_ssl. It contains directives telling Apache where to find encryption keys and certificates, the TLS protocol versions to allow, and the encryption ciphers to accept. This will be your local certificate file:
-
/etc/pki/tls/certs/apache-selfsigned.crt
This file contains both a self-signed certificate and the certificate's private key. Apache requires the certificate and key to be in PEM format, which consists of Base64-encoded ASCII characters framed by "BEGIN" and "END" lines, as in the following abbreviated example.
-----BEGIN PRIVATE KEY----- MIIEvgIBADANBgkqhkiG9w0BAQEFAASCBKgwggSkAgEAAoIBAQD2KKx/8Zk94m1q 3gQMZF9ZN66Ls19+3tHAgQ5Fpo9KJDhzLjOOCI8u1PTcGmAah5kEitCEc0wzmNeo BCl0wYR6G0rGaKtK9Dn7CuIjvubtUysVyQoMVPQ97ldeakHWeRMiEJFXg6kZZ0vr GvwnKoMh3DlK44D9dX7IDua2PlYx5+eroA+1Lqf32ZSaAO0bBIMIYTHigwbHMZoT ... 56tE7THvH7vOEf4/iUOsIrEzaMaJ0mqkmY1A70qQGQKBgBF3H1qNRNHuyMcPODFs 27hDzPDinrquSEvoZIggkDMlh2irTiipJ/GhkvTpoQlv0fK/VXw8vSgeaBuhwJvS LXU9HvYq0U6O4FgD3nAyB9hI0BE13r1HjUvbjT7moH+RhnNz6eqqdscCS09VtRAo 4QQvAqOa8UheYeoXLdWcHaLP -----END PRIVATE KEY----- -----BEGIN CERTIFICATE----- MIIEazCCA1OgAwIBAgICWxQwDQYJKoZIhvcNAQELBQAwgbExCzAJBgNVBAYTAi0t MRIwEAYDVQQIDAlTb21lU3RhdGUxETAPBgNVBAcMCFNvbWVDaXR5MRkwFwYDVQQK DBBTb21lT3JnYW5pemF0aW9uMR8wHQYDVQQLDBZTb21lT3JnYW5pemF0aW9uYWxV bml0MRkwFwYDVQQDDBBpcC0xNzItMzEtMjAtMjM2MSQwIgYJKoZIhvcNAQkBFhVy ... z5rRUE/XzxRLBZOoWZpNWTXJkQ3uFYH6s/sBwtHpKKZMzOvDedREjNKAvk4ws6F0 CuIjvubtUysVyQoMVPQ97ldeakHWeRMiEJFXg6kZZ0vrGvwnKoMh3DlK44D9dlU3 WanXWehT6FiSZvB4sTEXXJN2jdw8g+sHGnZ8zCOsclknYhHrCVD2vnBlZJKSZvak 3ZazhBxtQSukFMOnWPP2a0DMMFGYUHOd0BQE8sBJxg== -----END CERTIFICATE-----
The file names and extensions are a convenience and have no effect on function. For example, you can call a certificate
cert.crt
,cert.pem
, or any other file name, so long as the related directive in thessl.conf
file uses the same name.Note
When you replace the default TLS files with your own customized files, be sure that they are in PEM format.
-
-
Restart Apache.
[ec2-user ~]$
sudo systemctl restart httpd
Note
Make sure that TCP port 443 is accessible on your EC2 instance, as previously described.
-
Your Apache web server should now support HTTPS (secure HTTP) over port 443. Test it by entering the IP address or fully qualified domain name of your EC2 instance into a browser URL bar with the prefix
https://
.Because you are connecting to a site with a self-signed, untrusted host certificate, your browser may display a series of security warnings. Override the warnings and proceed to the site.
If the default Apache test page opens, it means that you have successfully configured TLS on your server. All data passing between the browser and server is now encrypted.
Note
To prevent site visitors from encountering warning screens, you must obtain a trusted, CA-signed certificate that not only encrypts, but also publicly authenticates you as the owner of the site.
Step 2: Obtain a CA-signed certificate
You can use the following process to obtain a CA-signed certificate:
-
Generate a certificate signing request (CSR) from a private key
-
Submit the CSR to a certificate authority (CA)
-
Obtain a signed host certificate
-
Configure Apache to use the certificate
A self-signed TLS X.509 host certificate is cryptologically identical to a CA-signed certificate. The difference is social, not mathematical. A CA promises, at a minimum, to validate a domain's ownership before issuing a certificate to an applicant. Each web browser contains a list of CAs trusted by the browser vendor to do this. An X.509 certificate consists primarily of a public key that corresponds to your private server key, and a signature by the CA that is cryptographically tied to the public key. When a browser connects to a web server over HTTPS, the server presents a certificate for the browser to check against its list of trusted CAs. If the signer is on the list, or accessible through a chain of trust consisting of other trusted signers, the browser negotiates a fast encrypted data channel with the server and loads the page.
Certificates generally cost money because of the labor involved in validating the
requests, so it pays to shop around. A few CAs offer basic-level certificates free of
charge. The most notable of these CAs is the Let's
Encrypt
If you plan to offer commercial-grade services, Amazon Certificate Manager is a good option.
Underlying the host certificate is the key. As of 2019, government
Important
These instructions for acquiring a CA-signed host certificate do not work unless you own a registered and hosted DNS domain.
To obtain a CA-signed certificate
-
Connect to your instance and navigate to /etc/pki/tls/private/. This is the directory where you store the server's private key for TLS. If you prefer to use an existing host key to generate the CSR, skip to Step 3. For more information about connecting to your instance, see Connecting to AL2023 instances
-
(Optional) Generate a new private key. Here are some examples of key configurations. Any of the resulting keys works with your web server, but they vary in the degree and type of security that they implement.
-
Example 1: Create a default RSA host key. The resulting file,
custom.key
, is a 2048-bit RSA private key.[ec2-user ~]$
sudo openssl genrsa -out custom.key
-
Example 2: Create a stronger RSA key with a bigger modulus. The resulting file,
custom.key
, is a 4096-bit RSA private key.[ec2-user ~]$
sudo openssl genrsa -out custom.key 4096
-
Example 3: Create a 4096-bit encrypted RSA key with password protection. The resulting file,
custom.key
, is a 4096-bit RSA private key encrypted with the AES-128 cipher.Important
Encrypting the key provides greater security, but because an encrypted key requires a password, services depending on it cannot be auto-started. Each time you use this key, you must supply the password (in the preceding example, "abcde12345") over an SSH connection.
[ec2-user ~]$
sudo openssl genrsa -aes128 -passout pass:abcde12345 -out custom.key 4096
-
Example 4: Create a key using a non-RSA cipher. RSA cryptography can be relatively slow because of the size of its public keys, which are based on the product of two large prime numbers. However, it is possible to create keys for TLS that use non-RSA ciphers. Keys based on the mathematics of elliptic curves are smaller and computationally faster when delivering an equivalent level of security.
[ec2-user ~]$
sudo openssl ecparam -name prime256v1 -out custom.key -genkey
The result is a 256-bit elliptic curve private key using prime256v1, a "named curve" that OpenSSL supports. Its cryptographic strength is slightly greater than a 2048-bit RSA key, according to NIST
. Note
Not all CAs provide the same level of support for elliptic-curve-based keys as for RSA keys.
Make sure that the new private key has highly restrictive ownership and permissions (owner=root, group=root, read/write for owner only). The commands would be as shown in the following example.
[ec2-user ~]$
sudo chown root:root custom.key
[ec2-user ~]$
sudo chmod 600 custom.key
[ec2-user ~]$
ls -al custom.key
The preceding commands yield the following result.
-rw------- root root custom.key
After you have created and configured a satisfactory key, you can create a CSR.
-
-
Create a CSR using your preferred key. The following example uses
custom.key
.[ec2-user ~]$
sudo openssl req -new -key custom.key -out csr.pem
OpenSSL opens a dialog and prompts you for the information shown in the following table. All of the fields except Common Name are optional for a basic, domain-validated host certificate.
Name Description Example Country Name The two-letter ISO abbreviation for your country. US (=United States) State or Province Name The name of the state or province where your organization is located. This name cannot be abbreviated. Washington Locality Name The location of your organization, such as a city. Seattle Organization Name The full legal name of your organization. Do not abbreviate your organization name. Example Corporation Organizational Unit Name Additional organizational information, if any. Example Dept Common Name This value must exactly match the web address that you expect users to enter into a browser. Usually, this means a domain name with a prefixed hostname or alias in the form
www.example.com
. In testing with a self-signed certificate and no DNS resolution, the common name may consist of the hostname alone. CAs also offer more expensive certificates that accept wild-card names such as*.example.com
.www.example.com Email Address The server administrator's email address. someone@example.com Finally, OpenSSL prompts you for an optional challenge password. This password applies only to the CSR and to transactions between you and your CA, so follow the CA's recommendations about this and the other optional field, optional company name. The CSR challenge password has no effect on server operation.
The resulting file
csr.pem
contains your public key, your digital signature of your public key, and the metadata that you entered. -
Submit the CSR to a CA. This usually consists of opening your CSR file in a text editor and copying the contents into a web form. At this time, you may be asked to supply one or more subject alternate names (SANs) to be placed on the certificate. If
www.example.com
is the common name, thenexample.com
would be a good SAN, and vice versa. A visitor to your site entering either of these names would see an error-free connection. If your CA web form allows it, include the common name in the list of SANs. Some CAs include it automatically.After your request has been approved, you receive a new host certificate signed by the CA. You might also be instructed to download an intermediate certificate file that contains additional certificates needed to complete the CA's chain of trust.
Note
Your CA might send you files in multiple formats intended for various purposes. For this tutorial, you should only use a certificate file in PEM format, which is usually (but not always) marked with a
.pem
or.crt
file extension. If you are uncertain which file to use, open the files with a text editor and find the one containing one or more blocks beginning with the following line.- - - - -BEGIN CERTIFICATE - - - - -
The file should also end with the following line.
- - - -END CERTIFICATE - - - - -
You can also test the file at the command line as shown in the following.
[ec2-user certs]$
openssl x509 -in
certificate.crt
-textVerify that these lines appear in the file. Do not use files ending with
.p7b
,.p7c
, or similar file extensions. -
Place the new CA-signed certificate and any intermediate certificates in the
/etc/pki/tls/certs
directory.Note
There are several ways to upload your new certificate to your EC2 instance, but the most straightforward and informative way is to open a text editor (for example, vi, nano, or notepad) on both your local computer and your instance, and then copy and paste the file contents between them. You need root [sudo] permissions when performing these operations on the EC2 instance. This way, you can see immediately if there are any permission or path problems. Be careful, however, not to add any additional lines while copying the contents, or to change them in any way.
From inside the
/etc/pki/tls/certs
directory, check that the file ownership, group, and permission settings match the highly restrictive AL2023 defaults (owner=root, group=root, read/write for owner only). The following example shows the commands to use.[ec2-user certs]$
sudo chown root:root custom.crt
[ec2-user certs]$
sudo chmod 600 custom.crt
[ec2-user certs]$
ls -al custom.crt
These commands should yield the following result.
-rw------- root root custom.crt
The permissions for the intermediate certificate file are less stringent (owner=root, group=root, owner can write, group can read, world can read). The following example shows the commands to use.
[ec2-user certs]$
sudo chown root:root intermediate.crt
[ec2-user certs]$
sudo chmod 644 intermediate.crt
[ec2-user certs]$
ls -al intermediate.crt
These commands should yield the following result.
-rw-r--r-- root root intermediate.crt
-
Place the private key that you used to create the CSR in the
/etc/pki/tls/private/
directory.Note
There are several ways to upload your custom key to your EC2 instance, but the most straightforward and informative way is to open a text editor (for example, vi, nano, or notepad) on both your local computer and your instance, and then copy and paste the file contents between them. You need root [sudo] permissions when performing these operations on the EC2 instance. This way, you can see immediately if there are any permission or path problems. Be careful, however, not to add any additional lines while copying the contents, or to change them in any way.
From inside the
/etc/pki/tls/private
directory, use the following commands to verify that the file ownership, group, and permission settings match the highly restrictive AL2023 defaults (owner=root, group=root, read/write for owner only).[ec2-user private]$
sudo chown root:root custom.key
[ec2-user private]$
sudo chmod 600 custom.key
[ec2-user private]$
ls -al custom.key
These commands should yield the following result.
-rw------- root root custom.key
-
Edit
/etc/httpd/conf.d/ssl.conf
to reflect your new certificate and key files.-
Provide the path and file name of the CA-signed host certificate in Apache's
SSLCertificateFile
directive:SSLCertificateFile /etc/pki/tls/certs/custom.crt
-
If you received an intermediate certificate file (
intermediate.crt
in this example), provide its path and file name using Apache'sSSLCACertificateFile
directive:SSLCACertificateFile /etc/pki/tls/certs/intermediate.crt
Note
Some CAs combine the host certificate and the intermediate certificates in a single file, making the
SSLCACertificateFile
directive unnecessary. Consult the instructions provided by your CA. -
Provide the path and file name of the private key (
custom.key
in this example) in Apache'sSSLCertificateKeyFile
directive:SSLCertificateKeyFile /etc/pki/tls/private/custom.key
-
-
Save
/etc/httpd/conf.d/ssl.conf
and restart Apache.[ec2-user ~]$
sudo systemctl restart httpd
-
Test your server by entering your domain name into a browser URL bar with the prefix
https://
. Your browser should load the test page over HTTPS without generating errors.
Step 3: Test and harden the security configuration
After your TLS is operational and exposed to the public, you should test how secure it
really is. This is easy to do using online services such as Qualys SSL Labs
Important
Real-world testing is crucial to the security of your server. Small configuration errors may lead to serious security breaches and loss of data. Because recommended security practices change constantly in response to research and emerging threats, periodic security audits are essential to good server administration.
On the Qualys SSL
Labswww.example.com
. After about two minutes, you receive a grade
(from A to F) for your site and a detailed breakdown of the findings. The following
table summarizes the report for a domain with settings identical to the default Apache
configuration on AL2023, and with a default Certbot certificate.
Overall rating | B |
Certificate | 100% |
Protocol support | 95% |
Key exchange | 70% |
Cipher strength | 90% |
Though the overview shows that the configuration is mostly sound, the detailed report flags several potential problems, listed here in order of severity:
✗ The RC4 cipher is supported for use by certain older
browsers. A cipher is the mathematical core of an encryption algorithm.
RC4, a fast cipher used to encrypt TLS data-streams, is known to have several serious
weaknesses
✗ Old TLS versions are supported. The configuration supports TLS 1.0 (already deprecated) and TLS 1.1 (on a path to deprecation). Only TLS 1.2 has been recommended since 2018.
✗ Forward secrecy is not fully supported.
Forward secrecy
To correct and future-proof the TLS configuration
-
Open the configuration file
/etc/httpd/conf.d/ssl.conf
in a text editor and comment out the following line by entering "#" at the beginning of the line.#SSLProtocol all -SSLv3
-
Add the following directive:
#SSLProtocol all -SSLv3 SSLProtocol -SSLv2 -SSLv3 -TLSv1 -TLSv1.1 +TLSv1.2
This directive explicitly disables SSL versions 2 and 3, as well as TLS versions 1.0 and 1.1. The server now refuses to accept encrypted connections with clients using anything except TLS 1.2. The verbose wording in the directive conveys more clearly, to a human reader, what the server is configured to do.
Note
Disabling TLS versions 1.0 and 1.1 in this manner blocks a small percentage of outdated web browsers from accessing your site.
To modify the list of allowed ciphers
-
In the configuration file
/etc/httpd/conf.d/ssl.conf
, find the section with theSSLCipherSuite
directive and comment out the existing line by entering "#" at the beginning of the line.#SSLCipherSuite HIGH:MEDIUM:!aNULL:!MD5
-
Specify explicit cipher suites and a cipher order that prioritizes forward secrecy and avoids insecure ciphers. The
SSLCipherSuite
directive used here is based on output from the Mozilla SSL Configuration Generator, which tailors a TLS configuration to the specific software running on your server. (For more information, see Mozilla's useful resource Security/Server Side TLS .) First determine your Apache and OpenSSL versions by using the output from the following commands. [ec2-user ~]$
yum list installed | grep httpd
[ec2-user ~]$
yum list installed | grep openssl
For example, if the returned information is Apache 2.4.34 and OpenSSL 1.0.2, we enter this into the generator. If you choose the "modern" compatibility model, this creates an
SSLCipherSuite
directive that aggressively enforces security but still works for most browsers. If your software doesn't support the modern configuration, you can update your software or choose the "intermediate" configuration instead.SSLCipherSuite ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305: ECDHE-RSA-CHACHA20-POLY1305:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256: ECDHE-ECDSA-AES256-SHA384:ECDHE-RSA-AES256-SHA384:ECDHE-ECDSA-AES128-SHA256:ECDHE-RSA-AES128-SHA256
The selected ciphers have ECDHE in their names, an abbreviation for Elliptic Curve Diffie-Hellman Ephemeral . The term ephemeral indicates forward secrecy. As a by-product, these ciphers do not support RC4.
We recommend that you use an explicit list of ciphers instead of relying on defaults or terse directives whose content isn't visible.
Copy the generated directive into
/etc/httpd/conf.d/ssl.conf
.Note
Though shown here on several lines for readability, the directive must be on a single line when copied to
/etc/httpd/conf.d/ssl.conf
, with only a colon (no spaces) between cipher names. -
Finally, uncomment the following line by removing the "#" at the beginning of the line.
#SSLHonorCipherOrder on
This directive forces the server to prefer high-ranking ciphers, including (in this case) those that support forward secrecy. With this directive turned on, the server tries to establish a strong secure connection before falling back to allowed ciphers with lesser security.
After completing both of these procedures, save the changes to
/etc/httpd/conf.d/ssl.conf
and restart Apache.
If you test the domain again on Qualys SSL Labs
Overall rating | A |
Certificate | 100% |
Protocol support | 100% |
Key exchange | 90% |
Cipher strength | 90% |
Each update to OpenSSL introduces new ciphers and removes support for old ones.
Keep your EC2 AL2023 instance up-to-date, watch for security announcements from
OpenSSL
Troubleshoot
-
My Apache webserver doesn't start unless I enter a password
This is expected behavior if you installed an encrypted, password-protected, private server key.
You can remove the encryption and password requirement from the key. Assuming that you have a private encrypted RSA key called
custom.key
in the default directory, and that the password on it isabcde12345
, run the following commands on your EC2 instance to generate an unencrypted version of the key.[ec2-user ~]$
cd /etc/pki/tls/private/
[ec2-user private]$
sudo cp custom.key custom.key.bak
[ec2-user private]$
sudo openssl rsa -in custom.key -passin pass:abcde12345 -out custom.key.nocrypt
[ec2-user private]$
sudo mv custom.key.nocrypt custom.key
[ec2-user private]$
sudo chown root:root custom.key
[ec2-user private]$
sudo chmod 600 custom.key
[ec2-user private]$
sudo systemctl restart httpd
Apache should now start without prompting you for a password.
-
I get errors when I run sudo dnf install -y mod_ssl.
When you are installing the required packages for SSL, you may see errors similar to the following.
Error: httpd24-tools conflicts with httpd-tools-2.2.34-1.16.amzn1.x86_64 Error: httpd24 conflicts with httpd-2.2.34-1.16.amzn1.x86_64
This typically means that your EC2 instance is not running AL2023. This tutorial only supports instances freshly created from an official AL2023 AMI.