| 1 | <?xml version='1.0' encoding='UTF-8'?>
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| 2 | <!DOCTYPE topic PUBLIC "-//OASIS//DTD DITA Topic//EN" "topic.dtd">
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| 3 | <topic xml:lang="en-us" id="vrde-crypt">
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| 4 | <title>RDP Encryption</title>
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| 5 |
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| 6 | <body>
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| 7 | <p>RDP features data stream encryption, which is based on the RC4 symmetric cipher, with keys up to 128-bit. The RC4
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| 8 | keys are replaced at regular intervals, every 4096 packets. </p>
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| 9 | <p>RDP provides the following different authentication methods: </p>
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| 10 | <ul>
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| 11 | <li>
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| 12 | <p><b outputclass="bold">RDP 4</b> authentication was
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| 13 | used historically. With RDP 4, the RDP client does not
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| 14 | perform any checks in order to verify the identity of the
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| 15 | server it connects to. Since user credentials can be
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| 16 | obtained using a man in the middle (MITM) attack, RDP4
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| 17 | authentication is insecure and should generally not be used.
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| 18 | </p>
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| 19 | </li>
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| 20 | <li>
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| 21 | <p><b outputclass="bold">RDP 5.1</b> authentication
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| 22 | employs a server certificate for which the client possesses
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| 23 | the public key. This way it is guaranteed that the server
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| 24 | possess the corresponding private key. However, as this
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| 25 | hard-coded private key became public some years ago, RDP 5.1
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| 26 | authentication is also insecure.
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| 27 | </p>
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| 28 | </li>
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| 29 | <li>
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| 30 | <p><b outputclass="bold">RDP 5.2 or later</b>
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| 31 | authentication uses Enhanced RDP Security, which means that
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| 32 | an external security protocol is used to secure the
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| 33 | connection. RDP 4 and RDP 5.1 use Standard RDP Security. The
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| 34 | VRDP server supports Enhanced RDP Security with TLS protocol
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| 35 | and, as a part of the TLS handshake, sends the server
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| 36 | certificate to the client.
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| 37 | </p>
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| 38 | <p>The <codeph>Security/Method</codeph> VRDE property sets the required security method, which is used for a
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| 39 | connection. Valid values are as follows: </p>
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| 40 | <ul>
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| 41 | <li>
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| 42 | <p><b outputclass="bold">Negotiate.</b> Both
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| 43 | Enhanced (TLS) and Standard RDP Security connections are
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| 44 | allowed. The security method is negotiated with the
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| 45 | client. This is the default setting.
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| 46 | </p>
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| 47 | </li>
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| 48 | <li>
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| 49 | <p><b outputclass="bold">RDP.</b> Only Standard RDP
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| 50 | Security is accepted.
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| 51 | </p>
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| 52 | </li>
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| 53 | <li>
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| 54 | <p><b outputclass="bold">TLS.</b> Only Enhanced RDP
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| 55 | Security is accepted. The client must support TLS.
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| 56 | </p>
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| 57 | <p>
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| 58 | The version of OpenSSL used by <ph conkeyref="vbox-conkeyref-phrases/product-name"/> supports
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| 59 | TLS versions 1.0, 1.1, 1.2, and 1.3.
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| 60 | </p>
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| 61 | </li>
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| 62 | </ul>
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| 63 | <p>For example, the following command enables a client to use either Standard or Enhanced RDP Security
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| 64 | connection: </p>
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| 65 | <pre xml:space="preserve">vboxmanage modifyvm <varname>VM-name</varname> --vrde-property "Security/Method=negotiate"</pre>
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| 66 | <p>If the <codeph>Security/Method</codeph> property is set to either Negotiate or TLS, the TLS protocol will be
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| 67 | automatically used by the server, if the client supports TLS. However, in order to use TLS the server must
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| 68 | possess the Server Certificate, the Server Private Key and the Certificate Authority (CA) Certificate. The
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| 69 | following example shows how to generate a server certificate. </p>
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| 70 | <ol>
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| 71 | <li>
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| 72 | <p>Create a CA self signed certificate. </p>
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| 73 | <pre xml:space="preserve">openssl req -new -x509 -days 365 -extensions v3_ca \
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| 74 | -keyout ca_key_private.pem -out ca_cert.pem</pre>
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| 75 | </li>
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| 76 | <li>
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| 77 | <p>Generate a server private key and a request for signing. </p>
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| 78 | <pre xml:space="preserve">openssl genrsa -out server_key_private.pem
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| 79 | openssl req -new -key server_key_private.pem -out server_req.pem</pre>
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| 80 | </li>
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| 81 | <li>
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| 82 | <p>Generate the server certificate. </p>
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| 83 | <pre xml:space="preserve">openssl x509 -req -days 365 -in server_req.pem \
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| 84 | -CA ca_cert.pem -CAkey ca_key_private.pem -set_serial 01 -out server_cert.pem</pre>
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| 85 | </li>
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| 86 | </ol>
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| 87 | <p>The server must be configured to access the required files. For example: </p>
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| 88 | <pre xml:space="preserve">vboxmanage modifyvm <varname>VM-name</varname> \
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| 89 | --vrde-property "Security/CACertificate=path/ca_cert.pem"</pre>
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| 90 | <pre xml:space="preserve">vboxmanage modifyvm <varname>VM-name</varname> \
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| 91 | --vrde-property "Security/ServerCertificate=path/server_cert.pem"</pre>
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| 92 | <pre xml:space="preserve">vboxmanage modifyvm <varname>VM-name</varname> \
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| 93 | --vrde-property "Security/ServerPrivateKey=path/server_key_private.pem"</pre>
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| 94 | </li>
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| 95 | </ul>
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| 96 | <p>As the client that connects to the server determines what type of encryption will be used, with
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| 97 | <userinput>rdesktop</userinput>, the Linux RDP viewer, use the <codeph>-4</codeph> or <codeph>-5</codeph>
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| 98 | options. </p>
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| 99 | </body>
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| 100 |
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| 101 | </topic>
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