security-doc/security-guide/source/secure-communication/tls-proxies-and-http-services.rst

TLS proxies and HTTP services

OpenStack endpoints are HTTP services providing APIs to both end-users on public networks and to other OpenStack services on the management network. It is highly recommended that all of these requests, both internal and external, operate over TLS. To achieve this goal, API services must be deployed behind a TLS proxy that can establish and terminate TLS sessions. The following table offers a non-exhaustive list of open source software that can be used for this purpose:

• Pound
• Stud
• Nginx
• Apache httpd

In cases where software termination offers insufficient performance, hardware accelerators may be worth exploring as an alternative option. It is important to be mindful of the size of requests that will be processed by any chosen TLS proxy.

Examples

Below we provide sample recommended configuration settings for enabling TLS in some of the more popular web servers/TLS terminators.

Before we delve into the configurations, we briefly discuss the ciphers' configuration element and its format. A more exhaustive treatment on available ciphers and the OpenSSL cipher list format can be found at: ciphers.

ciphers = "HIGH:!RC4:!MD5:!aNULL:!eNULL:!EXP:!LOW:!MEDIUM"

or

ciphers = "kEECDH:kEDH:kRSA:HIGH:!RC4:!MD5:!aNULL:!eNULL:!EXP:!LOW:!MEDIUM"

Cipher string options are separated by ":", while "!" provides negation of the immediately following element. Element order indicates preference unless overridden by qualifiers such as HIGH. Let us take a closer look at the elements in the above sample strings.

kEECDH:kEDH

Ephemeral Elliptic Curve Diffie-Hellman (abbreviated as EECDH and ECDHE).

Ephemeral Diffie-Hellman (abbreviated either as EDH or DHE) uses prime field groups.

Both approaches provide Perfect Forward Secrecy (PFS). See secure-communication-perfect-forward-secrecy for additional discussion on properly configuring PFS.

Ephemeral Elliptic Curves require the server to be configured with a named curve, and provide better security than prime field groups and at lower computational cost. However, prime field groups are more widely implemented, and thus typically both are included in list.

kRSA

Cipher suites using the RSA exchange, authentication or either respectively.

HIGH

Selects highest possible security cipher in the negotiation phase. These typically have keys of length 128 bits or longer.

!RC4

No RC4. RC4 has flaws in the context of TLS V3. See On the Security of RC4 in TLS and WPA.

!MD5

No MD5. MD5 is not collision resistant, and thus not acceptable for Message Authentication Codes (MAC) or signatures.

!aNULL:!eNULL

Disallows clear text.

!EXP

Disallows export encryption algorithms, which by design tend to be weak, typically using 40 and 56 bit keys.

US Export restrictions on cryptography systems have been lifted and no longer need to be supported.

!LOW:!MEDIUM

Disallows low (56 or 64 bit long keys) and medium (128 bit long keys) ciphers because of their vulnerability to brute force attacks (example 2-DES). This rule still permits Triple Data Encryption Standard (Triple DES) also known as Triple Data Encryption Algorithm (TDEA) and the Advanced Encryption Standard (AES), each of which has keys greater than equal to 128 bits and thus more secure.

Protocols

Protocols are enabled/disabled through SSL_CTX_set_options. We recommend disabling SSLv2/v3 and enabling TLS.

Pound

This Pound example enables AES-NI acceleration, which helps to improve performance on systems with processors that support this feature. The default configuration file is /etc/pound/pound.cfg on Ubuntu, /etc/pound.cfg on RHEL, CentOS, openSUSE, and SUSE Linux Enterprise.

## see pound(8) for details
daemon      1
######################################################################
## global options:
User        "swift"
Group       "swift"
#RootJail   "/chroot/pound"
## Logging: (goes to syslog by default)
##  0   no logging
##  1   normal
##  2   extended
##  3   Apache-style (common log format)
LogLevel    0
## turn on dynamic scaling (off by default)
# Dyn Scale 1
## check backend every X secs:
Alive       30
## client timeout
#Client     10
## allow 10 second proxy connect time
ConnTO      10
## use hardware-acceleration card supported by openssl(1):
SSLEngine   "aesni"
# poundctl control socket
Control "/var/run/pound/poundctl.socket"
######################################################################
## listen, redirect and ... to:
## redirect all swift requests on port 443 to local swift proxy
ListenHTTPS
    Address 0.0.0.0
    Port    443
    Cert    "/etc/pound/cert.pem"
    ## Certs to accept from clients
    ##  CAlist      "CA_file"
    ## Certs to use for client verification
    ##  VerifyList  "Verify_file"
    ## Request client cert - don't verify
    ##  Ciphers     "AES256-SHA"
    ## allow PUT and DELETE also (by default only GET, POST and HEAD)?:
    NoHTTPS11   0
    ## allow PUT and DELETE also (by default only GET, POST and HEAD)?:
    xHTTP       1
    Service
        BackEnd
            Address 127.0.0.1
            Port    80
        End
    End
End

Stud

The ciphers line can be tweaked based on your needs, however this is a reasonable starting place. The default configuration file is located in the /etc/stud directory. However, it is not provided by default.

# SSL x509 certificate file.
pem-file = "
# SSL protocol.
tls = on
ssl = off
# List of allowed SSL ciphers.
# OpenSSL's high-strength ciphers which require authentication
# NOTE: forbids clear text, use of RC4 or MD5 or LOW and MEDIUM strength ciphers
ciphers = "HIGH:!RC4:!MD5:!aNULL:!eNULL:!EXP:!LOW:!MEDIUM"
# Enforce server cipher list order
prefer-server-ciphers = on
# Number of worker processes
workers = 4
# Listen backlog size
backlog = 1000
# TCP socket keepalive interval in seconds
keepalive = 3600
# Chroot directory
chroot = ""
# Set uid after binding a socket
user = "www-data"
# Set gid after binding a socket
group = "www-data"
# Quiet execution, report only error messages
quiet = off
# Use syslog for logging
syslog = on
# Syslog facility to use
syslog-facility = "daemon"
# Run as daemon
daemon = off
# Report client address using SENDPROXY protocol for haproxy
# Disabling this until we upgrade to HAProxy 1.5
write-proxy = off

Nginx

This Nginx example requires TLS v1.1 or v1.2 for maximum security. The ssl_ciphers line can be tweaked based on your needs, however this is a reasonable starting place. The default configuration file is /etc/nginx/nginx.conf.

server {
    listen : ssl;
    ssl_certificate ;
    ssl_certificate_key ;
    ssl_protocols TLSv1.1 TLSv1.2;
    ssl_ciphers HIGH:!RC4:!MD5:!aNULL:!eNULL:!EXP:!LOW:!MEDIUM
    ssl_session_tickets off;

    server_name _;
    keepalive_timeout 5;

    location / {

    }
}

Apache

The default configuration file is /etc/apache2/apache2.conf on Ubuntu, /etc/httpd/conf/httpd.conf on RHEL and CentOS, /etc/apache2/httpd.conf on openSUSE and SUSE Linux Enterprise.

<VirtualHost <ip address>:80>
  ServerName <site FQDN>
  RedirectPermanent / https://<site FQDN>/
</VirtualHost>
<VirtualHost <ip address>:443>
  ServerName <site FQDN>
  SSLEngine On
  SSLProtocol +TLSv1 +TLSv1.1 +TLSv1.2,
  SSLCipherSuite HIGH:!RC4:!MD5:!aNULL:!eNULL:!EXP:!LOW:!MEDIUM
  SSLCertificateFile    /path/<site FQDN>.crt
  SSLCACertificateFile  /path/<site FQDN>.crt
  SSLCertificateKeyFile /path/<site FQDN>.key
  WSGIScriptAlias / <WSGI script location>
  WSGIDaemonProcess horizon user=<user> group=<group> processes=3 threads=10
  Alias /static <static files location>
  <Directory <WSGI dir>>
    # For http server 2.2 and earlier:
    Order allow,deny
    Allow from all

    # Or, in Apache http server 2.4 and later:
    # Require all granted
  </Directory>
</VirtualHost>

Compute API SSL endpoint in Apache, which you must pair with a short WSGI script.

<VirtualHost <ip address>:8447>
  ServerName <site FQDN>
  SSLEngine On
  SSLProtocol +TLSv1 +TLSv1.1 +TLSv1.2
  SSLCipherSuite HIGH:!RC4:!MD5:!aNULL:!eNULL:!EXP:!LOW:!MEDIUM
  SSLCertificateFile    /path/<site FQDN>.crt
  SSLCACertificateFile  /path/<site FQDN>.crt
  SSLCertificateKeyFile /path/<site FQDN>.key
  SSLSessionTickets Off
  WSGIScriptAlias / <WSGI script location>
  WSGIDaemonProcess osapi user=<user> group=<group> processes=3 threads=10
  <Directory <WSGI dir>>
    # For http server 2.2 and earlier:
    Order allow,deny
    Allow from all

    # Or, in Apache http server 2.4 and later:
    # Require all granted
  </Directory>
</VirtualHost>

HTTP strict transport security

We recommend that all production deployments use HTTP strict transport security (HSTS). This header prevents browsers from making insecure connections after they have made a single secure one. If you have deployed your HTTP services on a public or an untrusted domain, HSTS is especially important. To enable HSTS, configure your web server to send a header like this with all requests:

Strict-Transport-Security: max-age=31536000; includeSubDomains

Start with a short timeout of 1 day during testing, and raise it to one year after testing has shown that you have not introduced problems for users. Note that once this header is set to a large timeout, it is (by design) very difficult to disable.

Perfect forward secrecy

Configuring TLS servers for perfect forward secrecy requires careful planning around key size, session IDs, and session tickets. In addition, for multi-server deployments, shared state is also an important consideration. The example configurations for Apache and Nginx above disable the session tickets options to help mitigate some of these concerns. Real-world deployments may desire to enable this feature for improved performance. This can be done securely, but would require special consideration around key management. Such configurations are beyond the scope of this guide. We suggest reading How to botch TLS forward secrecy by ImperialViolet as a starting place for understanding the problem space.