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-[ Please note that this file has not been updated for OpenSSH and 
-  covers the ssh-1.2.12 release from Dec 1995 only. ]
-Ssh (Secure Shell) is a program to log into another computer over a
-network, to execute commands in a remote machine, and to move files
-from one machine to another.  It provides strong authentication and
-secure communications over insecure channels.  It is inteded as a
-replacement for rlogin, rsh, rcp, and rdist.
-See the file INSTALL for installation instructions.  See COPYING for
-license terms and other legal issues.  See RFC for a description of
-the protocol.  There is a WWW page for ssh; see http://www.cs.hut.fi/ssh.
-This file has been updated to match ssh-1.2.12.
-FEATURES
- o  Strong authentication.  Closes several security holes (e.g., IP,
-    routing, and DNS spoofing).  New authentication methods: .rhosts
-    together with RSA based host authentication, and pure RSA
-    authentication.
- o  Improved privacy.  All communications are automatically and
-    transparently encrypted.  RSA is used for key exchange, and a
-    conventional cipher (normally IDEA, DES, or triple-DES) for
-    encrypting the session.  Encryption is started before
-    authentication, and no passwords or other information is
-    transmitted in the clear.  Encryption is also used to protect
-    against spoofed packets.
- o  Secure X11 sessions.  The program automatically sets DISPLAY on
-    the server machine, and forwards any X11 connections over the
-    secure channel.  Fake Xauthority information is automatically
-    generated and forwarded to the remote machine; the local client
-    automatically examines incoming X11 connections and replaces the
-    fake authorization data with the real data (never telling the 
-    remote machine the real information).
- o  Arbitrary TCP/IP ports can be redirected through the encrypted channel
-    in both directions (e.g., for e-cash transactions).
- o  No retraining needed for normal users; everything happens
-    automatically, and old .rhosts files will work with strong
-    authentication if administration installs host key files.
- o  Never trusts the network.  Minimal trust on the remote side of
-    the connection.  Minimal trust on domain name servers.  Pure RSA
-    authentication never trusts anything but the private key.
- o  Client RSA-authenticates the server machine in the beginning of
-    every connection to prevent trojan horses (by routing or DNS
-    spoofing) and man-in-the-middle attacks, and the server
-    RSA-authenticates the client machine before accepting .rhosts or
-    /etc/hosts.equiv authentication (to prevent DNS, routing, or
-    IP-spoofing).
- o  Host authentication key distribution can be centrally by the
-    administration, automatically when the first connection is made
-    to a machine (the key obtained on the first connection will be
-    recorded and used for authentication in the future), or manually
-    by each user for his/her own use.  The central and per-user host
-    key repositories are both used and complement each other.  Host
-    keys can be generated centrally or automatically when the software
-    is installed.  Host authentication keys are typically 1024 bits.
- o  Any user can create any number of user authentication RSA keys for
-    his/her own use.  Each user has a file which lists the RSA public
-    keys for which proof of possession of the corresponding private
-    key is accepted as authentication.  User authentication keys are
-    typically 1024 bits.
- o  The server program has its own server RSA key which is
-    automatically regenerated every hour.  This key is never saved in
-    any file.  Exchanged session keys are encrypted using both the
-    server key and the server host key.  The purpose of the separate
-    server key is to make it impossible to decipher a captured session by
-    breaking into the server machine at a later time; one hour from
-    the connection even the server machine cannot decipher the session
-    key.  The key regeneration interval is configurable.  The server
-    key is normally 768 bits.
- o  An authentication agent, running in the user's laptop or local
-    workstation, can be used to hold the user's RSA authentication
-    keys.  Ssh automatically forwards the connection to the
-    authentication agent over any connections, and there is no need to
-    store the RSA authentication keys on any machine in the network
-    (except the user's own local machine).  The authentication
-    protocols never reveal the keys; they can only be used to verify
-    that the user's agent has a certain key.  Eventually the agent
-    could rely on a smart card to perform all authentication
-    computations.
- o  The software can be installed and used (with restricted
-    functionality) even without root privileges.
- o  The client is customizable in system-wide and per-user
-    configuration files.  Most aspects of the client's operation can
-    be configured.  Different options can be specified on a per-host basis.
- o  Automatically executes conventional rsh (after displaying a
-    warning) if the server machine is not running sshd.
- o  Optional compression of all data with gzip (including forwarded X11
-    and TCP/IP port data), which may result in significant speedups on
-    slow connections.
- o  Complete replacement for rlogin, rsh, and rcp.
-WHY TO USE SECURE SHELL
-Currently, almost all communications in computer networks are done
-without encryption.  As a consequence, anyone who has access to any
-machine connected to the network can listen in on any communication.
-This is being done by hackers, curious administrators, employers,
-criminals, industrial spies, and governments.  Some networks leak off
-enough electromagnetic radiation that data may be captured even from a
-distance.
-When you log in, your password goes in the network in plain
-text.  Thus, any listener can then use your account to do any evil he
-likes.  Many incidents have been encountered worldwide where crackers
-have started programs on workstations without the owners knowledge
-just to listen to the network and collect passwords.  Programs for
-doing this are available on the Internet, or can be built by a
-competent programmer in a few hours.
-Any information that you type or is printed on your screen can be
-monitored, recorded, and analyzed.  For example, an intruder who has
-penetrated a host connected to a major network can start a program
-that listens to all data flowing in the network, and whenever it
-encounters a 16-digit string, it checks if it is a valid credit card
-number (using the check digit), and saves the number plus any
-surrounding text (to catch expiration date and holder) in a file.
-When the intruder has collected a few thousand credit card numbers, he
-makes smallish mail-order purchases from a few thousand stores around
-the world, and disappears when the goods arrive but before anyone
-suspects anything.
-Businesses have trade secrets, patent applications in preparation,
-pricing information, subcontractor information, client data, personnel
-data, financial information, etc.  Currently, anyone with access to
-the network (any machine on the network) can listen to anything that
-goes in the network, without any regard to normal access restrictions.
-Many companies are not aware that information can so easily be
-recovered from the network.  They trust that their data is safe
-since nobody is supposed to know that there is sensitive information
-in the network, or because so much other data is transferred in the
-network.  This is not a safe policy.
-Individual persons also have confidential information, such as
-diaries, love letters, health care documents, information about their
-personal interests and habits, professional data, job applications,
-tax reports, political documents, unpublished manuscripts, etc.
-One should also be aware that economical intelligence and industrial
-espionage has recently become a major priority of the intelligence
-agencies of major governments.  President Clinton recently assigned
-economical espionage as the primary task of the CIA, and the French
-have repeatedly been publicly boasting about their achievements on
-this field.
-There is also another frightening aspect about the poor security of
-communications.  Computer storage and analysis capability has
-increased so much that it is feasible for governments, major
-companies, and criminal organizations to automatically analyze,
-identify, classify, and file information about millions of people over
-the years.  Because most of the work can be automated, the cost of
-collecting this information is getting very low.  
-Government agencies may be able to monitor major communication
-systems, telephones, fax, computer networks, etc., and passively
-collect huge amounts of information about all people with any
-significant position in the society.  Most of this information is not
-sensitive, and many people would say there is no harm in someone
-getting that information.  However, the information starts to get
-sensitive when someone has enough of it.  You may not mind someone
-knowing what you bought from the shop one random day, but you might
-not like someone knowing every small thing you have bought in the last
-ten years.
-If the government some day starts to move into a more totalitarian
-direction (one should remember that Nazi Germany was created by
-democratic elections), there is considerable danger of an ultimate
-totalitarian state.  With enough information (the automatically
-collected records of an individual can be manually analyzed when the
-person becomes interesting), one can form a very detailed picture of
-the individual's interests, opinions, beliefs, habits, friends,
-lovers, weaknesses, etc.  This information can be used to 1) locate
-any persons who might oppose the new system 2) use deception to
-disturb any organizations which might rise against the government 3)
-eliminate difficult individuals without anyone understanding what
-happened.  Additionally, if the government can monitor communications
-too effectively, it becomes too easy to locate and eliminate any
-persons distributing information contrary to the official truth.
-Fighting crime and terrorism are often used as grounds for domestic
-surveillance and restricting encryption.  These are good goals, but
-there is considerable danger that the surveillance data starts to get
-used for questionable purposes.  I find that it is better to tolerate
-a small amount of crime in the society than to let the society become
-fully controlled.  I am in favor of a fairly strong state, but the
-state must never get so strong that people become unable to spread
-contra-offical information and unable to overturn the government if it
-is bad.  The danger is that when you notice that the government is
-too powerful, it is too late.  Also, the real power may not be where
-the official government is.
-For these reasons (privacy, protecting trade secrets, and making it
-more difficult to create a totalitarian state), I think that strong
-cryptography should be integrated to the tools we use every day.
-Using it causes no harm (except for those who wish to monitor
-everything), but not using it can cause huge problems.  If the society
-changes in undesirable ways, then it will be to late to start
-encrypting.
-Encryption has had a "military" or "classified" flavor to it.  There
-are no longer any grounds for this.  The military can and will use its
-own encryption; that is no excuse to prevent the civilians from
-protecting their privacy and secrets.  Information on strong
-encryption is available in every major bookstore, scientific library,
-and patent office around the world, and strong encryption software is
-available in every country on the Internet.
-Some people would like to make it illegal to use encryption, or to
-force people to use encryption that governments can break.  This
-approach offers no protection if the government turns bad.  Also, the
-"bad guys" will be using true strong encryption anyway.  Good
-encryption techniques are too widely known to make them disappear.
-Thus, any "key escrow encryption" or other restrictions will only help
-monitor ordinary people and petty criminals.  It does not help against
-powerful criminals, terrorists, or espionage, because they will know
-how to use strong encryption anyway.  (One source for internationally
-available encryption software is http://www.cs.hut.fi/crypto.)
-OVERVIEW OF SECURE SHELL
-The software consists of a number of programs.
-   sshd         Server program run on the server machine.  This
-                listens for connections from client machines, and
-                whenever it receives a connection, it performs
-                authentication and starts serving the client.
-   ssh          This is the client program used to log into another
-                machine or to execute commands on the other machine.
-                "slogin" is another name for this program.
-   scp          Securely copies files from one machine to another.
-   ssh-keygen   Used to create RSA keys (host keys and user
-                authentication keys).
-   ssh-agent    Authentication agent.  This can be used to hold RSA
-                keys for authentication.
-   ssh-add      Used to register new keys with the agent.
-   make-ssh-known-hosts
-                Used to create the /etc/ssh_known_hosts file.
-Ssh is the program users normally use.  It is started as
-  ssh host
-or
-  ssh host command
-The first form opens a new shell on the remote machine (after
-authentication).  The latter form executes the command on the remote
-machine.
-When started, the ssh connects sshd on the server machine, verifies
-that the server machine really is the machine it wanted to connect,
-exchanges encryption keys (in a manner which prevents an outside
-listener from getting the keys), performs authentication using .rhosts
-and /etc/hosts.equiv, RSA authentication, or conventional password
-based authentication.  The server then (normally) allocates a
-pseudo-terminal and starts an interactive shell or user program.
-The TERM environment variable (describing the type of the user's
-terminal) is passed from the client side to the remote side.  Also,
-terminal modes will be copied from the client side to the remote side
-to preserve user preferences (e.g., the erase character).
-If the DISPLAY variable is set on the client side, the server will
-create a dummy X server and set DISPLAY accordingly.  Any connections
-to the dummy X server will be forwarded through the secure channel,
-and will be made to the real X server from the client side.  An
-arbitrary number of X programs can be started during the session, and
-starting them does not require anything special from the user.  (Note
-that the user must not manually set DISPLAY, because then it would
-connect directly to the real display instead of going through the
-encrypted channel).  This behavior can be disabled in the
-configuration file or by giving the -x option to the client.
-Arbitrary IP ports can be forwarded over the secure channel.  The
-program then creates a port on one side, and whenever a connection is
-opened to this port, it will be passed over the secure channel, and a
-connection will be made from the other side to a specified host:port
-pair.  Arbitrary IP forwarding must always be explicitly requested,
-and cannot be used to forward privileged ports (unless the user is
-root).  It is possible to specify automatic forwards in a per-user
-configuration file, for example to make electronic cash systems work
-securely.
-If there is an authentication agent on the client side, connection to
-it will be automatically forwarded to the server side.
-For more infomation, see the manual pages ssh(1), sshd(8), scp(1),
-ssh-keygen(1), ssh-agent(1), ssh-add(1), and make-ssh-known-hosts(1)
-included in this distribution.
-X11 CONNECTION FORWARDING
-X11 forwarding serves two purposes: it is a convenience to the user
-because there is no need to set the DISPLAY variable, and it provides
-encrypted X11 connections.  I cannot think of any other easy way to
-make X11 connections encrypted; modifying the X server, clients or
-libraries would require special work for each machine, vendor and
-application.  Widely used IP-level encryption does not seem likely for
-several years.  Thus what we have left is faking an X server on the
-same machine where the clients are run, and forwarding the connections
-to a real X server over the secure channel.
-X11 forwarding works as follows.  The client extracts Xauthority
-information for the server.  It then creates random authorization
-data, and sends the random data to the server.  The server allocates
-an X11 display number, and stores the (fake) Xauthority data for this
-display.  Whenever an X11 connection is opened, the server forwards
-the connection over the secure channel to the client, and the client
-parses the first packet of the X11 protocol, substitutes real
-authentication data for the fake data (if the fake data matched), and
-forwards the connection to the real X server.
-If the display does not have Xauthority data, the server will create a
-unix domain socket in /tmp/.X11-unix, and use the unix domain socket
-as the display.  No authentication information is forwarded in this
-case.  X11 connections are again forwarded over the secure channel.
-To the X server the connections appear to come from the client
-machine, and the server must have connections allowed from the local
-machine.  Using authentication data is always recommended because not
-using it makes the display insecure.  If XDM is used, it automatically
-generates the authentication data.
-One should be careful not to use "xin" or "xstart" or other similar
-scripts that explicitly set DISPLAY to start X sessions in a remote
-machine, because the connection will then not go over the secure
-channel.  The recommended way to start a shell in a remote machine is
-  xterm -e ssh host &
-and the recommended way to execute an X11 application in a remote
-machine is
-  ssh -n host emacs &
-If you need to type a password/passphrase for the remote machine,
-  ssh -f host emacs
-may be useful.
-RSA AUTHENTICATION
-RSA authentication is based on public key cryptograpy.  The idea is
-that there are two encryption keys, one for encryption and another for
-decryption.  It is not possible (on human timescale) to derive the
-decryption key from the encryption key.  The encryption key is called
-the public key, because it can be given to anyone and it is not
-secret.  The decryption key, on the other hand, is secret, and is
-called the private key.
-RSA authentication is based on the impossibility of deriving the
-private key from the public key.  The public key is stored on the
-server machine in the user's $HOME/.ssh/authorized_keys file.  The
-private key is only kept on the user's local machine, laptop, or other
-secure storage.  Then the user tries to log in, the client tells the
-server the public key that the user wishes to use for authentication.
-The server then checks if this public key is admissible.  If so, it
-generates a 256 bit random number, encrypts it with the public key,
-and sends the value to the client.  The client then decrypts the
-number with its private key, computes a 128 bit MD5 checksum from the
-resulting data, and sends the checksum back to the server.  (Only a
-checksum is sent to prevent chosen-plaintext attacks against RSA.)
-The server checks computes a checksum from the correct data,
-and compares the checksums.  Authentication is accepted if the
-checksums match.  (Theoretically this indicates that the client
-only probably knows the correct key, but for all practical purposes
-there is no doubt.)
-The RSA private key can be protected with a passphrase.  The
-passphrase can be any string; it is hashed with MD5 to produce an
-encryption key for IDEA, which is used to encrypt the private part of
-the key file.  With passphrase, authorization requires access to the key
-file and the passphrase.  Without passphrase, authorization only
-depends on possession of the key file.
-RSA authentication is the most secure form of authentication supported
-by this software.  It does not rely on the network, routers, domain
-name servers, or the client machine.  The only thing that matters is
-access to the private key.  
-All this, of course, depends on the security of the RSA algorithm
-itself.  RSA has been widely known since about 1978, and no effective
-methods for breaking it are known if it is used properly.  Care has
-been taken to avoid the well-known pitfalls.  Breaking RSA is widely
-believed to be equivalent to factoring, which is a very hard
-mathematical problem that has received considerable public research.
-So far, no effective methods are known for numbers bigger than about
-512 bits.  However, as computer speeds and factoring methods are
-increasing, 512 bits can no longer be considered secure.  The
-factoring work is exponential, and 768 or 1024 bits are widely
-considered to be secure in the near future.
-RHOSTS AUTHENTICATION
-Conventional .rhosts and hosts.equiv based authentication mechanisms
-are fundamentally insecure due to IP, DNS (domain name server) and
-routing spoofing attacks.  Additionally this authentication method
-relies on the integrity of the client machine.  These weaknesses is
-tolerable, and been known and exploited for a long time.
-Ssh provides an improved version of these types of authentication,
-because they are very convenient for the user (and allow easy
-transition from rsh and rlogin).  It permits these types of
-authentication, but additionally requires that the client host be
-authenticated using RSA.  
-The server has a list of host keys stored in /etc/ssh_known_host, and
-additionally each user has host keys in $HOME/.ssh/known_hosts.  Ssh
-uses the name servers to obtain the canonical name of the client host,
-looks for its public key in its known host files, and requires the
-client to prove that it knows the private host key.  This prevents IP
-and routing spoofing attacks (as long as the client machine private
-host key has not been compromized), but is still vulnerable to DNS
-attacks (to a limited extent), and relies on the integrity of the
-client machine as to who is requesting to log in.  This prevents
-outsiders from attacking, but does not protect against very powerful
-attackers.  If maximal security is desired, only RSA authentication
-should be used.
-It is possible to enable conventional .rhosts and /etc/hosts.equiv
-authentication (without host authentication) at compile time by giving
-the option --with-rhosts to configure.  However, this is not
-recommended, and is not done by default.
-These weaknesses are present in rsh and rlogin.  No improvement in
-security will be obtained unless rlogin and rsh are completely
-disabled (commented out in /etc/inetd.conf).  This is highly
-recommended.
-WEAKEST LINKS IN SECURITY
-One should understand that while this software may provide
-cryptographically secure communications, it may be easy to
-monitor the communications at their endpoints.
-Basically, anyone with root access on the local machine on which you
-are running the software may be able to do anything.  Anyone with root
-access on the server machine may be able to monitor your
-communications, and a very talented root user might even be able to
-send his/her own requests to your authentication agent.
-One should also be aware that computers send out electromagnetic
-radition that can sometimes be picked up hundreds of meters away.
-Your keyboard is particularly easy to listen to.  The image on your
-monitor might also be seen on another monitor in a van parked behind
-your house.
-Beware that unwanted visitors might come to your home or office and
-use your machine while you are away.  They might also make
-modifications or install bugs in your hardware or software.
-Beware that the most effective way for someone to decrypt your data
-may be with a rubber hose.
-LEGAL ISSUES
-As far as I am concerned, anyone is permitted to use this software
-freely.  However, see the file COPYING for detailed copying,
-licensing, and distribution information.
-In some countries, particularly France, Russia, Iraq, and Pakistan,
-it may be illegal to use any encryption at all without a special
-permit, and the rumor has it that you cannot get a permit for any
-strong encryption.
-This software may be freely imported into the United States; however,
-the United States Government may consider re-exporting it a criminal
-offence.
-Note that any information and cryptographic algorithms used in this
-software are publicly available on the Internet and at any major
-bookstore, scientific library, or patent office worldwide.
-THERE IS NO WARRANTY FOR THIS PROGRAM.  Please consult the file
-COPYING for more information.
-MAILING LISTS AND OTHER INFORMATION
-There is a mailing list for ossh.  It is ossh@sics.se.  If you would
-like to join, send a message to majordomo@sics.se with "subscribe
-ssh" in body.
-The WWW home page for ssh is http://www.cs.hut.fi/ssh.  It contains an
-archive of the mailing list, and detailed information about new
-releases, mailing lists, and other relevant issues.
-Bug reports should be sent to ossh-bugs@sics.se.
-ABOUT THE AUTHOR
-This software was written by Tatu Ylonen <ylo@cs.hut.fi>.  I work as a
-researcher at Helsinki University of Technology, Finland.  For more
-information, see http://www.cs.hut.fi/~ylo/.  My PGP public key is
-available via finger from ylo@cs.hut.fi and from the key servers.  I
-prefer PGP encrypted mail.
-The author can be contacted via ordinary mail at
-  Tatu Ylonen
-  Helsinki University of Technology
-  Otakaari 1
-  FIN-02150 ESPOO
-  Finland
-  Fax. +358-0-4513293
-ACKNOWLEDGEMENTS
-I thank Tero Kivinen, Timo Rinne, Janne Snabb, and Heikki Suonsivu for
-their help and comments in the design, implementation and porting of
-this software.  I also thank numerous contributors, including but not
-limited to Walker Aumann, Jurgen Botz, Hans-Werner Braun, Stephane
-Bortzmeyer, Adrian Colley, Michael Cooper, David Dombek, Jerome
-Etienne, Bill Fithen, Mark Fullmer, Bert Gijsbers, Andreas Gustafsson,
-Michael Henits, Steve Johnson, Thomas Koenig, Felix Leitner, Gunnar
-Lindberg, Andrew Macpherson, Marc Martinec, Paul Mauvais, Donald
-McKillican, Leon Mlakar, Robert Muchsel, Mark Treacy, Bryan
-O'Sullivan, Mikael Suokas, Ollivier Robert, Jakob Schlyter, Tomasz
-Surmacz, Alvar Vinacua, Petri Virkkula, Michael Warfield, and
-Cristophe Wolfhugel.
-Thanks also go to Philip Zimmermann, whose PGP software and the
-associated legal battle provided inspiration, motivation, and many
-useful techniques, and to Bruce Schneier whose book Applied
-Cryptography has done a great service in widely distributing knowledge
-about cryptographic methods.
-Copyright (c) 1995 Tatu Ylonen, Espoo, Finland.