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README

      1 [ A Japanese translation of this document is available at
      2 [ http://www.unixuser.org/%7Eharuyama/security/openssh/index.html
      3 [ Thanks to HARUYAMA Seigo <haruyama (a] nt.phys.s.u-tokyo.ac.jp>
      4 
      5 ******* IMPORTANT
      6 * On systmes which lack a /dev/random driver, version of this port
      7 * prior to 1.2.2 were not correctly seeding OpenSSL's random number
      8 * pool. This resulted in lower quality RSA keys being generated. If
      9 * you generated host or user keys with v1.2.2 or previous versions, 
     10 * please generate new ones using a more recent version.
     11 
     12 This is the port of OpenBSD's excellent OpenSSH[0] to Linux and other
     13 Unices.
     14 
     15 OpenSSH is based on the last free version of Tatu Ylonen's SSH with
     16 all patent-encumbered algorithms removed (to external libraries), all
     17 known security bugs fixed, new features reintroduced and many other
     18 clean-ups. More information about SSH itself can be found in the file
     19 README.Ylonen. OpenSSH has been created by Aaron Campbell, Bob Beck,
     20 Markus Friedl, Niels Provos, Theo de Raadt, and Dug Song. It has a
     21 homepage at http://www.openssh.com/
     22 
     23 This port consists of the re-introduction of autoconf support, PAM
     24 support (for Linux and Solaris), EGD[1] support and replacements for 
     25 OpenBSD library functions that are (regrettably) absent from other 
     26 unices. This port has been best tested on Linux, Solaris, HPUX, NetBSD 
     27 and Irix. Support for AIX, SCO, NeXT and other Unices is underway. 
     28 This version actively tracks changes in the OpenBSD CVS repository.
     29 
     30 The PAM support is now more functional than the popular packages of
     31 commercial ssh-1.2.x. It checks "account" and "session" modules for
     32 all logins, not just when using password authentication.
     33 
     34 OpenSSH depends on Zlib[2], OpenSSL[3] and optionally PAM[4].
     35 
     36 There is now several mailing lists for this port of OpenSSH. Please
     37 refer to http://www.openssh.com/list.html for details on how to join.
     38 
     39 Please send bug reports and patches to the mailing list
     40 openssh-unix-dev (a] mindrot.org. The list is open to posting by
     41 unsubscribed users.
     42 
     43 If you are a citizen of the USA or another country which restricts 
     44 export of cryptographic products, then please refrain from sending 
     45 crypto-related code or patches to the list. We cannot accept them.
     46 Other code contribution are accepted, but please follow the OpenBSD
     47 style guidelines[5].
     48 
     49 Please refer to the INSTALL document for information on how to install
     50 OpenSSH on your system. There are a number of differences between this 
     51 port of OpenSSH and F-Secure SSH 1.x, please refer to the OpenSSH FAQ[6]
     52 for details and general tips.
     53 
     54 Damien Miller <djm (a] mindrot.org>
     55 
     56 Miscellania - 
     57 
     58 This version of SSH is based upon code retrieved from the OpenBSD CVS
     59 repository which in turn was based on the last free 
     60 version of SSH released by Tatu Ylonen.
     61 
     62 References -
     63 
     64 [0] http://www.openssh.com/faq.html
     65 [1] http://www.lothar.com/tech/crypto/
     66 [2] ftp://ftp.freesoftware.com/pub/infozip/zlib/
     67 [3] http://www.openssl.org/
     68 [4] http://www.kernel.org/pub/linux/libs/pam/ (PAM is standard on Solaris)
     69 [5] http://www.openbsd.org/cgi-bin/man.cgi?query=style&sektion=9&apropos=0&manpath=OpenBSD+Current
     70 [6] http://www.openssh.com/faq.html
     71 

README.Ylonen

      1 
      2 [ Please note that this file has not been updated for OpenSSH and 
      3   covers the ssh-1.2.12 release from Dec 1995 only. ]
      4 
      5 Ssh (Secure Shell) is a program to log into another computer over a
      6 network, to execute commands in a remote machine, and to move files
      7 from one machine to another.  It provides strong authentication and
      8 secure communications over insecure channels.  It is inteded as a
      9 replacement for rlogin, rsh, rcp, and rdist.
     10 
     11 See the file INSTALL for installation instructions.  See COPYING for
     12 license terms and other legal issues.  See RFC for a description of
     13 the protocol.  There is a WWW page for ssh; see http://www.cs.hut.fi/ssh.
     14 
     15 This file has been updated to match ssh-1.2.12.
     16 
     17 
     18 FEATURES
     19 
     20  o  Strong authentication.  Closes several security holes (e.g., IP,
     21     routing, and DNS spoofing).  New authentication methods: .rhosts
     22     together with RSA based host authentication, and pure RSA
     23     authentication.
     24 
     25  o  Improved privacy.  All communications are automatically and
     26     transparently encrypted.  RSA is used for key exchange, and a
     27     conventional cipher (normally IDEA, DES, or triple-DES) for
     28     encrypting the session.  Encryption is started before
     29     authentication, and no passwords or other information is
     30     transmitted in the clear.  Encryption is also used to protect
     31     against spoofed packets.
     32 
     33  o  Secure X11 sessions.  The program automatically sets DISPLAY on
     34     the server machine, and forwards any X11 connections over the
     35     secure channel.  Fake Xauthority information is automatically
     36     generated and forwarded to the remote machine; the local client
     37     automatically examines incoming X11 connections and replaces the
     38     fake authorization data with the real data (never telling the 
     39     remote machine the real information).
     40 
     41  o  Arbitrary TCP/IP ports can be redirected through the encrypted channel
     42     in both directions (e.g., for e-cash transactions).
     43 
     44  o  No retraining needed for normal users; everything happens
     45     automatically, and old .rhosts files will work with strong
     46     authentication if administration installs host key files.
     47 
     48  o  Never trusts the network.  Minimal trust on the remote side of
     49     the connection.  Minimal trust on domain name servers.  Pure RSA
     50     authentication never trusts anything but the private key.
     51 
     52  o  Client RSA-authenticates the server machine in the beginning of
     53     every connection to prevent trojan horses (by routing or DNS
     54     spoofing) and man-in-the-middle attacks, and the server
     55     RSA-authenticates the client machine before accepting .rhosts or
     56     /etc/hosts.equiv authentication (to prevent DNS, routing, or
     57     IP-spoofing).
     58 
     59  o  Host authentication key distribution can be centrally by the
     60     administration, automatically when the first connection is made
     61     to a machine (the key obtained on the first connection will be
     62     recorded and used for authentication in the future), or manually
     63     by each user for his/her own use.  The central and per-user host
     64     key repositories are both used and complement each other.  Host
     65     keys can be generated centrally or automatically when the software
     66     is installed.  Host authentication keys are typically 1024 bits.
     67 
     68  o  Any user can create any number of user authentication RSA keys for
     69     his/her own use.  Each user has a file which lists the RSA public
     70     keys for which proof of possession of the corresponding private
     71     key is accepted as authentication.  User authentication keys are
     72     typically 1024 bits.
     73 
     74  o  The server program has its own server RSA key which is
     75     automatically regenerated every hour.  This key is never saved in
     76     any file.  Exchanged session keys are encrypted using both the
     77     server key and the server host key.  The purpose of the separate
     78     server key is to make it impossible to decipher a captured session by
     79     breaking into the server machine at a later time; one hour from
     80     the connection even the server machine cannot decipher the session
     81     key.  The key regeneration interval is configurable.  The server
     82     key is normally 768 bits.
     83 
     84  o  An authentication agent, running in the user's laptop or local
     85     workstation, can be used to hold the user's RSA authentication
     86     keys.  Ssh automatically forwards the connection to the
     87     authentication agent over any connections, and there is no need to
     88     store the RSA authentication keys on any machine in the network
     89     (except the user's own local machine).  The authentication
     90     protocols never reveal the keys; they can only be used to verify
     91     that the user's agent has a certain key.  Eventually the agent
     92     could rely on a smart card to perform all authentication
     93     computations.
     94 
     95  o  The software can be installed and used (with restricted
     96     functionality) even without root privileges.
     97 
     98  o  The client is customizable in system-wide and per-user
     99     configuration files.  Most aspects of the client's operation can
    100     be configured.  Different options can be specified on a per-host basis.
    101 
    102  o  Automatically executes conventional rsh (after displaying a
    103     warning) if the server machine is not running sshd.
    104 
    105  o  Optional compression of all data with gzip (including forwarded X11
    106     and TCP/IP port data), which may result in significant speedups on
    107     slow connections.
    108 
    109  o  Complete replacement for rlogin, rsh, and rcp.
    110 
    111 
    112 WHY TO USE SECURE SHELL
    113 
    114 Currently, almost all communications in computer networks are done
    115 without encryption.  As a consequence, anyone who has access to any
    116 machine connected to the network can listen in on any communication.
    117 This is being done by hackers, curious administrators, employers,
    118 criminals, industrial spies, and governments.  Some networks leak off
    119 enough electromagnetic radiation that data may be captured even from a
    120 distance.
    121 
    122 When you log in, your password goes in the network in plain
    123 text.  Thus, any listener can then use your account to do any evil he
    124 likes.  Many incidents have been encountered worldwide where crackers
    125 have started programs on workstations without the owners knowledge
    126 just to listen to the network and collect passwords.  Programs for
    127 doing this are available on the Internet, or can be built by a
    128 competent programmer in a few hours.
    129 
    130 Any information that you type or is printed on your screen can be
    131 monitored, recorded, and analyzed.  For example, an intruder who has
    132 penetrated a host connected to a major network can start a program
    133 that listens to all data flowing in the network, and whenever it
    134 encounters a 16-digit string, it checks if it is a valid credit card
    135 number (using the check digit), and saves the number plus any
    136 surrounding text (to catch expiration date and holder) in a file.
    137 When the intruder has collected a few thousand credit card numbers, he
    138 makes smallish mail-order purchases from a few thousand stores around
    139 the world, and disappears when the goods arrive but before anyone
    140 suspects anything.
    141 
    142 Businesses have trade secrets, patent applications in preparation,
    143 pricing information, subcontractor information, client data, personnel
    144 data, financial information, etc.  Currently, anyone with access to
    145 the network (any machine on the network) can listen to anything that
    146 goes in the network, without any regard to normal access restrictions.
    147 
    148 Many companies are not aware that information can so easily be
    149 recovered from the network.  They trust that their data is safe
    150 since nobody is supposed to know that there is sensitive information
    151 in the network, or because so much other data is transferred in the
    152 network.  This is not a safe policy.
    153 
    154 Individual persons also have confidential information, such as
    155 diaries, love letters, health care documents, information about their
    156 personal interests and habits, professional data, job applications,
    157 tax reports, political documents, unpublished manuscripts, etc.
    158 
    159 One should also be aware that economical intelligence and industrial
    160 espionage has recently become a major priority of the intelligence
    161 agencies of major governments.  President Clinton recently assigned
    162 economical espionage as the primary task of the CIA, and the French
    163 have repeatedly been publicly boasting about their achievements on
    164 this field.
    165 
    166 
    167 There is also another frightening aspect about the poor security of
    168 communications.  Computer storage and analysis capability has
    169 increased so much that it is feasible for governments, major
    170 companies, and criminal organizations to automatically analyze,
    171 identify, classify, and file information about millions of people over
    172 the years.  Because most of the work can be automated, the cost of
    173 collecting this information is getting very low.  
    174 
    175 Government agencies may be able to monitor major communication
    176 systems, telephones, fax, computer networks, etc., and passively
    177 collect huge amounts of information about all people with any
    178 significant position in the society.  Most of this information is not
    179 sensitive, and many people would say there is no harm in someone
    180 getting that information.  However, the information starts to get
    181 sensitive when someone has enough of it.  You may not mind someone
    182 knowing what you bought from the shop one random day, but you might
    183 not like someone knowing every small thing you have bought in the last
    184 ten years.
    185 
    186 If the government some day starts to move into a more totalitarian
    187 direction (one should remember that Nazi Germany was created by
    188 democratic elections), there is considerable danger of an ultimate
    189 totalitarian state.  With enough information (the automatically
    190 collected records of an individual can be manually analyzed when the
    191 person becomes interesting), one can form a very detailed picture of
    192 the individual's interests, opinions, beliefs, habits, friends,
    193 lovers, weaknesses, etc.  This information can be used to 1) locate
    194 any persons who might oppose the new system 2) use deception to
    195 disturb any organizations which might rise against the government 3)
    196 eliminate difficult individuals without anyone understanding what
    197 happened.  Additionally, if the government can monitor communications
    198 too effectively, it becomes too easy to locate and eliminate any
    199 persons distributing information contrary to the official truth.
    200 
    201 Fighting crime and terrorism are often used as grounds for domestic
    202 surveillance and restricting encryption.  These are good goals, but
    203 there is considerable danger that the surveillance data starts to get
    204 used for questionable purposes.  I find that it is better to tolerate
    205 a small amount of crime in the society than to let the society become
    206 fully controlled.  I am in favor of a fairly strong state, but the
    207 state must never get so strong that people become unable to spread
    208 contra-offical information and unable to overturn the government if it
    209 is bad.  The danger is that when you notice that the government is
    210 too powerful, it is too late.  Also, the real power may not be where
    211 the official government is.
    212 
    213 For these reasons (privacy, protecting trade secrets, and making it
    214 more difficult to create a totalitarian state), I think that strong
    215 cryptography should be integrated to the tools we use every day.
    216 Using it causes no harm (except for those who wish to monitor
    217 everything), but not using it can cause huge problems.  If the society
    218 changes in undesirable ways, then it will be to late to start
    219 encrypting.
    220 
    221 Encryption has had a "military" or "classified" flavor to it.  There
    222 are no longer any grounds for this.  The military can and will use its
    223 own encryption; that is no excuse to prevent the civilians from
    224 protecting their privacy and secrets.  Information on strong
    225 encryption is available in every major bookstore, scientific library,
    226 and patent office around the world, and strong encryption software is
    227 available in every country on the Internet.
    228 
    229 Some people would like to make it illegal to use encryption, or to
    230 force people to use encryption that governments can break.  This
    231 approach offers no protection if the government turns bad.  Also, the
    232 "bad guys" will be using true strong encryption anyway.  Good
    233 encryption techniques are too widely known to make them disappear.
    234 Thus, any "key escrow encryption" or other restrictions will only help
    235 monitor ordinary people and petty criminals.  It does not help against
    236 powerful criminals, terrorists, or espionage, because they will know
    237 how to use strong encryption anyway.  (One source for internationally
    238 available encryption software is http://www.cs.hut.fi/crypto.)
    239 
    240 
    241 OVERVIEW OF SECURE SHELL
    242 
    243 The software consists of a number of programs.
    244 
    245    sshd		Server program run on the server machine.  This
    246    		listens for connections from client machines, and
    247 		whenever it receives a connection, it performs
    248 		authentication and starts serving the client.
    249 
    250    ssh		This is the client program used to log into another
    251 		machine or to execute commands on the other machine.
    252 		"slogin" is another name for this program.
    253 
    254    scp		Securely copies files from one machine to another.
    255 
    256    ssh-keygen	Used to create RSA keys (host keys and user
    257    		authentication keys).
    258 
    259    ssh-agent	Authentication agent.  This can be used to hold RSA
    260    		keys for authentication.
    261 
    262    ssh-add	Used to register new keys with the agent.
    263 
    264    make-ssh-known-hosts
    265    		Used to create the /etc/ssh_known_hosts file.
    266 
    267 
    268 Ssh is the program users normally use.  It is started as
    269 
    270   ssh host
    271 
    272 or
    273 
    274   ssh host command
    275 
    276 The first form opens a new shell on the remote machine (after
    277 authentication).  The latter form executes the command on the remote
    278 machine.
    279 
    280 When started, the ssh connects sshd on the server machine, verifies
    281 that the server machine really is the machine it wanted to connect,
    282 exchanges encryption keys (in a manner which prevents an outside
    283 listener from getting the keys), performs authentication using .rhosts
    284 and /etc/hosts.equiv, RSA authentication, or conventional password
    285 based authentication.  The server then (normally) allocates a
    286 pseudo-terminal and starts an interactive shell or user program.
    287 
    288 The TERM environment variable (describing the type of the user's
    289 terminal) is passed from the client side to the remote side.  Also,
    290 terminal modes will be copied from the client side to the remote side
    291 to preserve user preferences (e.g., the erase character).
    292 
    293 If the DISPLAY variable is set on the client side, the server will
    294 create a dummy X server and set DISPLAY accordingly.  Any connections
    295 to the dummy X server will be forwarded through the secure channel,
    296 and will be made to the real X server from the client side.  An
    297 arbitrary number of X programs can be started during the session, and
    298 starting them does not require anything special from the user.  (Note
    299 that the user must not manually set DISPLAY, because then it would
    300 connect directly to the real display instead of going through the
    301 encrypted channel).  This behavior can be disabled in the
    302 configuration file or by giving the -x option to the client.
    303 
    304 Arbitrary IP ports can be forwarded over the secure channel.  The
    305 program then creates a port on one side, and whenever a connection is
    306 opened to this port, it will be passed over the secure channel, and a
    307 connection will be made from the other side to a specified host:port
    308 pair.  Arbitrary IP forwarding must always be explicitly requested,
    309 and cannot be used to forward privileged ports (unless the user is
    310 root).  It is possible to specify automatic forwards in a per-user
    311 configuration file, for example to make electronic cash systems work
    312 securely.
    313 
    314 If there is an authentication agent on the client side, connection to
    315 it will be automatically forwarded to the server side.
    316 
    317 For more infomation, see the manual pages ssh(1), sshd(8), scp(1),
    318 ssh-keygen(1), ssh-agent(1), ssh-add(1), and make-ssh-known-hosts(1)
    319 included in this distribution.
    320 
    321 
    322 X11 CONNECTION FORWARDING
    323 
    324 X11 forwarding serves two purposes: it is a convenience to the user
    325 because there is no need to set the DISPLAY variable, and it provides
    326 encrypted X11 connections.  I cannot think of any other easy way to
    327 make X11 connections encrypted; modifying the X server, clients or
    328 libraries would require special work for each machine, vendor and
    329 application.  Widely used IP-level encryption does not seem likely for
    330 several years.  Thus what we have left is faking an X server on the
    331 same machine where the clients are run, and forwarding the connections
    332 to a real X server over the secure channel.
    333 
    334 X11 forwarding works as follows.  The client extracts Xauthority
    335 information for the server.  It then creates random authorization
    336 data, and sends the random data to the server.  The server allocates
    337 an X11 display number, and stores the (fake) Xauthority data for this
    338 display.  Whenever an X11 connection is opened, the server forwards
    339 the connection over the secure channel to the client, and the client
    340 parses the first packet of the X11 protocol, substitutes real
    341 authentication data for the fake data (if the fake data matched), and
    342 forwards the connection to the real X server.
    343 
    344 If the display does not have Xauthority data, the server will create a
    345 unix domain socket in /tmp/.X11-unix, and use the unix domain socket
    346 as the display.  No authentication information is forwarded in this
    347 case.  X11 connections are again forwarded over the secure channel.
    348 To the X server the connections appear to come from the client
    349 machine, and the server must have connections allowed from the local
    350 machine.  Using authentication data is always recommended because not
    351 using it makes the display insecure.  If XDM is used, it automatically
    352 generates the authentication data.
    353 
    354 One should be careful not to use "xin" or "xstart" or other similar
    355 scripts that explicitly set DISPLAY to start X sessions in a remote
    356 machine, because the connection will then not go over the secure
    357 channel.  The recommended way to start a shell in a remote machine is
    358 
    359   xterm -e ssh host &
    360 
    361 and the recommended way to execute an X11 application in a remote
    362 machine is
    363 
    364   ssh -n host emacs &
    365 
    366 If you need to type a password/passphrase for the remote machine,
    367 
    368   ssh -f host emacs
    369 
    370 may be useful.
    371 
    372 
    373 
    374 RSA AUTHENTICATION
    375 
    376 RSA authentication is based on public key cryptograpy.  The idea is
    377 that there are two encryption keys, one for encryption and another for
    378 decryption.  It is not possible (on human timescale) to derive the
    379 decryption key from the encryption key.  The encryption key is called
    380 the public key, because it can be given to anyone and it is not
    381 secret.  The decryption key, on the other hand, is secret, and is
    382 called the private key.
    383 
    384 RSA authentication is based on the impossibility of deriving the
    385 private key from the public key.  The public key is stored on the
    386 server machine in the user's $HOME/.ssh/authorized_keys file.  The
    387 private key is only kept on the user's local machine, laptop, or other
    388 secure storage.  Then the user tries to log in, the client tells the
    389 server the public key that the user wishes to use for authentication.
    390 The server then checks if this public key is admissible.  If so, it
    391 generates a 256 bit random number, encrypts it with the public key,
    392 and sends the value to the client.  The client then decrypts the
    393 number with its private key, computes a 128 bit MD5 checksum from the
    394 resulting data, and sends the checksum back to the server.  (Only a
    395 checksum is sent to prevent chosen-plaintext attacks against RSA.)
    396 The server checks computes a checksum from the correct data,
    397 and compares the checksums.  Authentication is accepted if the
    398 checksums match.  (Theoretically this indicates that the client
    399 only probably knows the correct key, but for all practical purposes
    400 there is no doubt.)
    401 
    402 The RSA private key can be protected with a passphrase.  The
    403 passphrase can be any string; it is hashed with MD5 to produce an
    404 encryption key for IDEA, which is used to encrypt the private part of
    405 the key file.  With passphrase, authorization requires access to the key
    406 file and the passphrase.  Without passphrase, authorization only
    407 depends on possession of the key file.
    408 
    409 RSA authentication is the most secure form of authentication supported
    410 by this software.  It does not rely on the network, routers, domain
    411 name servers, or the client machine.  The only thing that matters is
    412 access to the private key.  
    413 
    414 All this, of course, depends on the security of the RSA algorithm
    415 itself.  RSA has been widely known since about 1978, and no effective
    416 methods for breaking it are known if it is used properly.  Care has
    417 been taken to avoid the well-known pitfalls.  Breaking RSA is widely
    418 believed to be equivalent to factoring, which is a very hard
    419 mathematical problem that has received considerable public research.
    420 So far, no effective methods are known for numbers bigger than about
    421 512 bits.  However, as computer speeds and factoring methods are
    422 increasing, 512 bits can no longer be considered secure.  The
    423 factoring work is exponential, and 768 or 1024 bits are widely
    424 considered to be secure in the near future.
    425 
    426 
    427 RHOSTS AUTHENTICATION
    428 
    429 Conventional .rhosts and hosts.equiv based authentication mechanisms
    430 are fundamentally insecure due to IP, DNS (domain name server) and
    431 routing spoofing attacks.  Additionally this authentication method
    432 relies on the integrity of the client machine.  These weaknesses is
    433 tolerable, and been known and exploited for a long time.
    434 
    435 Ssh provides an improved version of these types of authentication,
    436 because they are very convenient for the user (and allow easy
    437 transition from rsh and rlogin).  It permits these types of
    438 authentication, but additionally requires that the client host be
    439 authenticated using RSA.  
    440 
    441 The server has a list of host keys stored in /etc/ssh_known_host, and
    442 additionally each user has host keys in $HOME/.ssh/known_hosts.  Ssh
    443 uses the name servers to obtain the canonical name of the client host,
    444 looks for its public key in its known host files, and requires the
    445 client to prove that it knows the private host key.  This prevents IP
    446 and routing spoofing attacks (as long as the client machine private
    447 host key has not been compromized), but is still vulnerable to DNS
    448 attacks (to a limited extent), and relies on the integrity of the
    449 client machine as to who is requesting to log in.  This prevents
    450 outsiders from attacking, but does not protect against very powerful
    451 attackers.  If maximal security is desired, only RSA authentication
    452 should be used.
    453 
    454 It is possible to enable conventional .rhosts and /etc/hosts.equiv
    455 authentication (without host authentication) at compile time by giving
    456 the option --with-rhosts to configure.  However, this is not
    457 recommended, and is not done by default.
    458 
    459 These weaknesses are present in rsh and rlogin.  No improvement in
    460 security will be obtained unless rlogin and rsh are completely
    461 disabled (commented out in /etc/inetd.conf).  This is highly
    462 recommended.
    463 
    464 
    465 WEAKEST LINKS IN SECURITY
    466 
    467 One should understand that while this software may provide
    468 cryptographically secure communications, it may be easy to
    469 monitor the communications at their endpoints.
    470 
    471 Basically, anyone with root access on the local machine on which you
    472 are running the software may be able to do anything.  Anyone with root
    473 access on the server machine may be able to monitor your
    474 communications, and a very talented root user might even be able to
    475 send his/her own requests to your authentication agent.
    476 
    477 One should also be aware that computers send out electromagnetic
    478 radition that can sometimes be picked up hundreds of meters away.
    479 Your keyboard is particularly easy to listen to.  The image on your
    480 monitor might also be seen on another monitor in a van parked behind
    481 your house.
    482 
    483 Beware that unwanted visitors might come to your home or office and
    484 use your machine while you are away.  They might also make
    485 modifications or install bugs in your hardware or software.
    486 
    487 Beware that the most effective way for someone to decrypt your data
    488 may be with a rubber hose.
    489 
    490 
    491 LEGAL ISSUES
    492 
    493 As far as I am concerned, anyone is permitted to use this software
    494 freely.  However, see the file COPYING for detailed copying,
    495 licensing, and distribution information.
    496 
    497 In some countries, particularly France, Russia, Iraq, and Pakistan,
    498 it may be illegal to use any encryption at all without a special
    499 permit, and the rumor has it that you cannot get a permit for any
    500 strong encryption.
    501 
    502 This software may be freely imported into the United States; however,
    503 the United States Government may consider re-exporting it a criminal
    504 offence.
    505 
    506 Note that any information and cryptographic algorithms used in this
    507 software are publicly available on the Internet and at any major
    508 bookstore, scientific library, or patent office worldwide.
    509 
    510 THERE IS NO WARRANTY FOR THIS PROGRAM.  Please consult the file
    511 COPYING for more information.
    512 
    513 
    514 MAILING LISTS AND OTHER INFORMATION
    515 
    516 There is a mailing list for ossh.  It is ossh (a] sics.se.  If you would
    517 like to join, send a message to majordomo (a] sics.se with "subscribe
    518 ssh" in body.
    519 
    520 The WWW home page for ssh is http://www.cs.hut.fi/ssh.  It contains an
    521 archive of the mailing list, and detailed information about new
    522 releases, mailing lists, and other relevant issues.
    523 
    524 Bug reports should be sent to ossh-bugs (a] sics.se.
    525 
    526 
    527 ABOUT THE AUTHOR
    528 
    529 This software was written by Tatu Ylonen <ylo (a] cs.hut.fi>.  I work as a
    530 researcher at Helsinki University of Technology, Finland.  For more
    531 information, see http://www.cs.hut.fi/~ylo/.  My PGP public key is
    532 available via finger from ylo (a] cs.hut.fi and from the key servers.  I
    533 prefer PGP encrypted mail.
    534 
    535 The author can be contacted via ordinary mail at
    536   Tatu Ylonen
    537   Helsinki University of Technology
    538   Otakaari 1
    539   FIN-02150 ESPOO
    540   Finland
    541 
    542   Fax. +358-0-4513293
    543 
    544 
    545 ACKNOWLEDGEMENTS
    546 
    547 I thank Tero Kivinen, Timo Rinne, Janne Snabb, and Heikki Suonsivu for
    548 their help and comments in the design, implementation and porting of
    549 this software.  I also thank numerous contributors, including but not
    550 limited to Walker Aumann, Jurgen Botz, Hans-Werner Braun, Stephane
    551 Bortzmeyer, Adrian Colley, Michael Cooper, David Dombek, Jerome
    552 Etienne, Bill Fithen, Mark Fullmer, Bert Gijsbers, Andreas Gustafsson,
    553 Michael Henits, Steve Johnson, Thomas Koenig, Felix Leitner, Gunnar
    554 Lindberg, Andrew Macpherson, Marc Martinec, Paul Mauvais, Donald
    555 McKillican, Leon Mlakar, Robert Muchsel, Mark Treacy, Bryan
    556 O'Sullivan, Mikael Suokas, Ollivier Robert, Jakob Schlyter, Tomasz
    557 Surmacz, Alvar Vinacua, Petri Virkkula, Michael Warfield, and
    558 Cristophe Wolfhugel.
    559 
    560 Thanks also go to Philip Zimmermann, whose PGP software and the
    561 associated legal battle provided inspiration, motivation, and many
    562 useful techniques, and to Bruce Schneier whose book Applied
    563 Cryptography has done a great service in widely distributing knowledge
    564 about cryptographic methods.
    565 
    566 
    567 Copyright (c) 1995 Tatu Ylonen, Espoo, Finland.
    568