| 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>
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| 8 | RDP features data stream encryption, which is based on the RC4
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| 9 | symmetric cipher, with keys up to 128-bit. The RC4 keys are
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| 10 | replaced at regular intervals, every 4096 packets.
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| 11 | </p>
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| 12 | <p>
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| 13 | RDP provides the following different authentication methods:
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| 14 | </p>
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| 15 | <ul>
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| 16 | <li>
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| 17 | <p><b outputclass="bold">RDP 4</b> authentication was
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| 18 | used historically. With RDP 4, the RDP client does not
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| 19 | perform any checks in order to verify the identity of the
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| 20 | server it connects to. Since user credentials can be
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| 21 | obtained using a man in the middle (MITM) attack, RDP4
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| 22 | authentication is insecure and should generally not be used.
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| 23 | </p>
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| 24 | </li>
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| 25 | <li>
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| 26 | <p><b outputclass="bold">RDP 5.1</b> authentication
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| 27 | employs a server certificate for which the client possesses
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| 28 | the public key. This way it is guaranteed that the server
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| 29 | possess the corresponding private key. However, as this
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| 30 | hard-coded private key became public some years ago, RDP 5.1
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| 31 | authentication is also insecure.
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| 32 | </p>
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| 33 | </li>
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| 34 | <li>
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| 35 | <p><b outputclass="bold">RDP 5.2 or later</b>
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| 36 | authentication uses Enhanced RDP Security, which means that
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| 37 | an external security protocol is used to secure the
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| 38 | connection. RDP 4 and RDP 5.1 use Standard RDP Security. The
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| 39 | VRDP server supports Enhanced RDP Security with TLS protocol
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| 40 | and, as a part of the TLS handshake, sends the server
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| 41 | certificate to the client.
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| 42 | </p>
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| 43 | <p>
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| 44 | The <codeph>Security/Method</codeph> VRDE property sets
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| 45 | the desired security method, which is used for a connection.
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| 46 | Valid values are as follows:
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| 47 | </p>
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| 48 | <ul>
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| 49 | <li>
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| 50 | <p><b outputclass="bold">Negotiate.</b> Both
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| 51 | Enhanced (TLS) and Standard RDP Security connections are
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| 52 | allowed. The security method is negotiated with the
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| 53 | client. This is the default setting.
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| 54 | </p>
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| 55 | </li>
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| 56 | <li>
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| 57 | <p><b outputclass="bold">RDP.</b> Only Standard RDP
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| 58 | Security is accepted.
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| 59 | </p>
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| 60 | </li>
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| 61 | <li>
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| 62 | <p><b outputclass="bold">TLS.</b> Only Enhanced RDP
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| 63 | Security is accepted. The client must support TLS.
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| 64 | </p>
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| 65 | <p>
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| 66 | The version of OpenSSL used by Oracle VM VirtualBox supports
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| 67 | TLS versions 1.0, 1.1, 1.2, and 1.3.
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| 68 | </p>
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| 69 | </li>
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| 70 | </ul>
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| 71 | <p>
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| 72 | For example, the following command enables a client to use
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| 73 | either Standard or Enhanced RDP Security connection:
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| 74 | </p>
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| 75 | <pre xml:space="preserve">vboxmanage modifyvm <varname>VM-name</varname> --vrde-property "Security/Method=negotiate"</pre>
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| 76 | <p>
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| 77 | If the <codeph>Security/Method</codeph> property is set to
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| 78 | either Negotiate or TLS, the TLS protocol will be
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| 79 | automatically used by the server, if the client supports
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| 80 | TLS. However, in order to use TLS the server must possess
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| 81 | the Server Certificate, the Server Private Key and the
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| 82 | Certificate Authority (CA) Certificate. The following
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| 83 | example shows how to generate a server certificate.
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| 84 | </p>
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| 85 | <ol>
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| 86 | <li>
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| 87 | <p>
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| 88 | Create a CA self signed certificate.
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| 89 | </p>
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| 90 | <pre xml:space="preserve">openssl req -new -x509 -days 365 -extensions v3_ca \
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| 91 | -keyout ca_key_private.pem -out ca_cert.pem</pre>
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| 92 | </li>
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| 93 | <li>
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| 94 | <p>
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| 95 | Generate a server private key and a request for signing.
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| 96 | </p>
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| 97 | <pre xml:space="preserve">openssl genrsa -out server_key_private.pem
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| 98 | openssl req -new -key server_key_private.pem -out server_req.pem</pre>
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| 99 | </li>
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| 100 | <li>
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| 101 | <p>
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| 102 | Generate the server certificate.
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| 103 | </p>
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| 104 | <pre xml:space="preserve">openssl x509 -req -days 365 -in server_req.pem \
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| 105 | -CA ca_cert.pem -CAkey ca_key_private.pem -set_serial 01 -out server_cert.pem</pre>
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| 106 | </li>
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| 107 | </ol>
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| 108 | <p>
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| 109 | The server must be configured to access the required files.
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| 110 | For example:
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| 111 | </p>
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| 112 | <pre xml:space="preserve">vboxmanage modifyvm <varname>VM-name</varname> \
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| 113 | --vrde-property "Security/CACertificate=path/ca_cert.pem"</pre>
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| 114 | <pre xml:space="preserve">vboxmanage modifyvm <varname>VM-name</varname> \
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| 115 | --vrde-property "Security/ServerCertificate=path/server_cert.pem"</pre>
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| 116 | <pre xml:space="preserve">vboxmanage modifyvm <varname>VM-name</varname> \
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| 117 | --vrde-property "Security/ServerPrivateKey=path/server_key_private.pem"</pre>
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| 118 | </li>
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| 119 | </ul>
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| 120 | <p>
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| 121 | As the client that connects to the server determines what type
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| 122 | of encryption will be used, with <userinput>rdesktop</userinput>,
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| 123 | the Linux RDP viewer, use the <codeph>-4</codeph> or
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| 124 | <codeph>-5</codeph> options.
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| 125 | </p>
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| 126 | </body>
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| 127 |
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| 128 | </topic>
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