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1 | <!doctype html> |
2 | <html> | |
3 | <!-- SECTION: Getting Started --> | |
4 | <head> | |
5 | <title>Managing Encryption</title> | |
6 | <link rel="STYLESHEET" type="text/css" href="../cups-printable.css"> | |
7 | </head> | |
8 | <body> | |
9 | <h1 class="title">Managing Encryption</h1> | |
10 | <p>CUPS supports TLS encryption in two ways:</p> | |
11 | <ol> | |
12 | <li>Using HTTPS (always on) as soon as a connection is established, and</li> | |
13 | <li>Using HTTP Upgrade to TLS (opportunistic) after the connection is established.</li> | |
14 | </ol> | |
15 | <p>CUPS supports self-signed, CA-signed, and enterprise certificates, with configurable certificate validation, cipher suite, and SSL/TLS version policies.</p> | |
16 | <p>Out of the box, CUPS uses a Trust On First Use ("TOFU") certificate validation policy like the popular Secure Shell (ssh) software, requires TLS/1.0 or higher, only allows secure cipher suites, and automatically creates a "self-signed" certificate and private key for the scheduler so that remote administration operations and printer sharing are encrypted by default.</p> | |
17 | ||
18 | <h2>Configuring Client TLS Policies</h2> | |
19 | <p>The <a href="man-client.conf.html"><var>client.conf</var></a> file controls the client TLS policies. The default policy is:</p> | |
20 | <pre class="command"> | |
21 | AllowAnyRoot Yes | |
22 | AllowExpiredCerts No | |
23 | Encryption IfRequested | |
24 | SSLOptions None | |
25 | TrustOnFirstUse Yes | |
26 | ValidateCerts No | |
27 | </pre> | |
28 | <p>A client can be configured to only communicate with trusted TLS/1.1+ servers and printers by copying the corresponding certificates to the client (<a href="#PLATFORM">see below</a>) and using the following policy in the <var>client.conf</var> file or macOS<sup>®</sup> printing preferences:</p> | |
29 | <pre class="command"> | |
30 | AllowAnyRoot No | |
31 | AllowExpiredCerts No | |
32 | Encryption Required | |
33 | SSLOptions DenyTLS1.0 | |
34 | TrustOnFirstUse No | |
35 | ValidateCerts Yes | |
36 | </pre> | |
37 | <p>Similarly, if a client needs to support an older server that only supports SSL/3.0 and RC4 cipher suites you can use the following policy option:</p> | |
38 | <pre class="command"> | |
39 | SSLOptions AllowRC4 AllowSSL3 | |
40 | </pre> | |
41 | ||
42 | <h2>Configuring Server TLS Policies</h2> | |
43 | <p>Two directives in the <a href="man-cups-files.conf.html"><var>cups-files.conf</var></a> file control the server (scheduler) TLS policies - <a href="man-cups-files.conf.html#CreateSelfSignedCerts"><code>CreateSelfSignedCerts</code></a> and <a href="man-cups-files.conf.html#ServerKeychain"><code>ServerKeychain</code></a>. The default policy creates self-signed certificates as needed.</p> | |
44 | <p>The <a href="man-cupsd.conf.html#DefaultEncryption"><code>DefaultEncryption</code></a> and <a href="man-cupsd.conf.html#Encryption"><code>Encryption</code></a> directives in the <a href="man-cupsd.conf.html"><var>cupsd.conf</var></a> file control whether encryption is used. The default configuration requires encryption for remote access whenever authentication is required.</p> | |
45 | ||
46 | <h2><a name="PLATFORM">Platform Differences</a></h2> | |
47 | <h3>macOS<sup>®</sup></h3> | |
48 | <p>On macOS, client configuration settings for ordinary users are stored in the <var>~/Library/Preferences/org.cups.PrintingPrefs.plist</var> file. System-wide and user certificates are stored in the system and login keychains, with private CUPS keychains being used for self-signed and CUPS-managed certificates.</p> | |
49 | <h3>Windows<sup>®</sup></h3> | |
50 | <p>On Windows, client configuration settings are controlled by the SSL/TLS Group Policy settings and certificate stores.</p> | |
51 | <h3>Other Platforms</h3> | |
52 | <p>Other platforms only use the <var>client.conf</var> file and PEM-encoded certificates (<i>hostname</i>.crt) and private keys (<i>hostname</i>.key) in the <var>/etc/cups/ssl</var> and <var>~/.cups/ssl</var> directories. If present, the <var>/etc/cups/ssl/site.crt</var> file defines a site-wide CA certificate that is used to validate server and printer certificates. Certificates for known servers and printers are stored by CUPS in the corresponding <var>ssl</var> directory so they can be validated for subsequent connections.</p> | |
53 | <p>CUPS also supports certificates created and managed by the popular <a href="https://letsencrypt.org/">Let's Encrypt</a> certificate service, which are stored in the <var>/etc/letsencrypt/live</var> directory.</p> | |
54 | </body> | |
55 | </html> |