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diff --git a/lib/ssh/doc/src/introduction.xml b/lib/ssh/doc/src/introduction.xml index b42910cb34..70c6fb2ee1 100644 --- a/lib/ssh/doc/src/introduction.xml +++ b/lib/ssh/doc/src/introduction.xml @@ -25,31 +25,181 @@ <title>Introduction</title> <prepared>OTP team</prepared> + <responsible></responsible> + <docno></docno> + <approved></approved> + <checked></checked> + <date></date> + <rev></rev> <file>introduction.xml</file> </header> - + <p>SSH is a protocol for secure remote logon and + other secure network services over an insecure network.</p> <section> - <title>Purpose</title> + <title>Scope and Purpose</title> - <p>Secure Shell (SSH) is a protocol for secure remote login and - other secure network services over an insecure network. SSH - provides a single, full-duplex, byte-oriented connection between + <p>SSH provides a single, full-duplex, and byte-oriented connection between client and server. The protocol also provides privacy, integrity, - server authentication and man-in-the-middle protection.</p> - - <p>The Erlang SSH application is an implementation of the SSH - protocol in Erlang which offers API functions to write customized - SSH clients and servers as well as making the Erlang shell - available via SSH. Also included in the SSH application are an - SFTP (SSH File Transfer Protocol) client <seealso - marker="ssh_sftp">ssh_sftp</seealso> and server <seealso - marker="ssh_sftp">ssh_sftpd</seealso>.</p> + server authentication, and man-in-the-middle protection.</p> + + <p>The <c>ssh</c> application is an implementation of the SSH Transport + Layer Protocol in Erlang. It provides the following:</p> + <list type="bulleted"> + <item>API functions to write customized SSH clients and servers</item> + <item>The Erlang shell available through SSH</item> + <item>An SFTP client (<seealso marker="ssh_sftp">ssh_sftp</seealso>) + and server (<seealso marker="ssh_sftp">ssh_sftpd</seealso>)</item> + </list> </section> <section> <title>Prerequisites</title> - <p>It is assumed that the reader is familiar with the concepts of <seealso marker="doc/design_principles:des_princ">OTP</seealso> - and has a basic understanding of <url href="http://en.wikipedia.org/wiki/Public-key_cryptography">public keys</url>.</p> + <p>It is assumed that the reader is familiar with the Erlang programming language, + concepts of <em>OTP</em>, and has a basic understanding of <em>public keys</em>.</p> + </section> + +<section> + <title>SSH Protocol Overview</title> + + <p>Conceptually, the SSH protocol can be partitioned into four + layers:</p> + + <image file="SSH_protocols.png"> + <icaption>SSH Protocol Architecture</icaption> + </image> + + <section> + <title>Transport Protocol</title> + + <p>The SSH Transport Protocol is a secure, low-level transport. + It provides strong encryption, cryptographic host + authentication, and integrity protection. A minimum of + Message Authentication Code (MAC) and encryption + algorithms are supported. For details, see the + <seealso marker="ssh">ssh(3)</seealso> manual page in <c>ssh</c>.</p> + </section> + + <section> + <title>Authentication Protocol</title> + + <p>The SSH Authentication Protocol is a general-purpose user + authentication protocol run over the SSH Transport Layer + Protocol. The <c>ssh</c> application supports user authentication as follows: + </p> + <list type="bulleted"> + <item> + Using public key technology. RSA and DSA, X509-certificates + are not supported. + </item> + <item> + Using keyboard-interactive authentication. + This is suitable for interactive authentication methods + that do not need any special software support on the client side. + Instead, all authentication data is entered from the keyboard. + </item> + <item> + Using a pure password-based authentication scheme. + Here, the plain text password is encrypted before sent + over the network. + </item> + </list> + <p>Several configuration options for + authentication handling are available in + <seealso marker="ssh#connect-3">ssh:connect/[3,4]</seealso> + and <seealso marker="ssh#daemon-2">ssh:daemon/[2,3]</seealso>.</p> + <p> + The public key handling can be customized by implementing + the following behaviours from <c>ssh</c>:</p> + <list type="bulleted"> + <item>Module + <seealso marker="ssh_client_key_api">ssh_client_key_api</seealso>. + </item> + <item>Module + <seealso marker="ssh_server_key_api">ssh_server_key_api</seealso>. + </item> + </list> + </section> + + <section> + <title>Connection Protocol</title> + + <p>The SSH Connection Protocol provides application-support + services over the transport pipe, for example, channel multiplexing, + flow control, remote program execution, signal propagation, and + connection forwarding. Functions for handling the SSH + Connection Protocol can be found in the module <seealso + marker="ssh_connection">ssh_connection</seealso> in <c>ssh</c>. + </p> + </section> + + <section> + <title>Channels</title> + + <p>All terminal sessions, forwarded connections, and so on, are + channels. Multiple channels are multiplexed into a single + connection. All channels are flow-controlled. This means that no + data is sent to a channel peer until a message is received to + indicate that window space is available. + The <em>initial window size</em> specifies how many bytes of channel + data that can be sent to the channel peer without adjusting the + window. Typically, an SSH client opens a channel, sends data (commands), + receives data (control information), and then closes the channel. + The <seealso marker="ssh_channel">ssh_channel</seealso> behaviour + handles generic parts of SSH channel management. This makes it easy + to write your own SSH client/server processes that use flow-control + and thus opens for more focus on the application logic. + </p> + + <p>Channels come in the following three flavors:</p> + + <list type="bulleted"> + <item><em>Subsystem</em> - Named services that can be run as + part of an SSH server, such as SFTP <seealso + marker="ssh_sftpd">(ssh_sftpd)</seealso>, that is built into the + SSH daemon (server) by default, but it can be disabled. The Erlang <c>ssh</c> + daemon can be configured to run any Erlang- + implemented SSH subsystem. + </item> + <item><em>Shell</em> - Interactive shell. By default the + Erlang daemon runs the Erlang shell. The shell can be customized by + providing your own read-eval-print loop. You can also provide your + own Command-Line Interface (CLI) implementation, + but that is much more work. + </item> + <item><em>Exec</em> - One-time remote execution of commands. See function + <seealso marker="ssh_connection#exec-4">ssh_connection:exec/4</seealso> + for more information.</item> + </list> + </section> + + + </section> + <section> + <title>Where to Find More Information</title> + <p> + For detailed information about the SSH protocol, refer to the + following Request for Comments(RFCs): + </p> + + <list type="bulleted"> + <item><url href="http://www.ietf.org/rfc/rfc4250.txt">RFC 4250</url> - + Protocol Assigned Numbers</item> + <item><url href="http://www.ietf.org/rfc/rfc4251.txt">RFC 4251</url> - + Protocol Architecture</item> + <item><url href="http://www.ietf.org/rfc/rfc4252.txt">RFC 4252</url> - + Authentication Protocol</item> + <item><url href="http://www.ietf.org/rfc/rfc4253.txt">RFC 4253</url> - + Transport Layer Protocol</item> + <item><url href="http://www.ietf.org/rfc/rfc4254.txt">RFC 4254</url> - + Connection Protocol</item> + <item><url href="http://www.ietf.org/rfc/rfc4255.txt">RFC 4255</url> - + Key Fingerprints</item> + <item><url href="http://www.ietf.org/rfc/rfc4344.txt">RFC 4344</url> - + Transport Layer Encryption Modes</item> + <item><url href="http://www.ietf.org/rfc/rfc4716.txt">RFC 4716</url> - + Public Key File Format</item> + </list> + </section> </chapter> |