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NAME

       ssh - Main API of the ssh application

DESCRIPTION

       Interface module for the ssh application.

       See ssh(7) for details of supported version, algorithms and unicode support.

OPTIONS

       The  exact  behaviour  of  some  functions  can  be adjusted with the use of options which are documented
       together with the functions. Generally could each option be used at most one time in each function  call.
       If given two or more times, the effect is not predictable unless explicitly documented.

       The options are of different kinds:

         Limits:
           which alters limits in the system, for example number of simultaneous login attempts.

         Timeouts:
           which  give  some  defined  behaviour  if  too  long time elapses before a given event or action, for
           example time to wait for an answer.

         Callbacks:
           which gives the caller of the function the possibility to  execute  own  code  on  some  events,  for
           example calling an own logging function or to perform an own login function

         Behaviour:
           which changes the systems behaviour.

DATA TYPES

       Type  definitions  that  are used more than once in this module, or abstractions to indicate the intended
       use of the data type, or both:

         boolean() =:
           true | false

         string() =:
           [byte()]

         ssh_daemon_ref() =:
           opaque() - as returned by ssh:daemon/[1,2,3]

         ssh_connection_ref() =:
           opaque() - as returned by ssh:connect/3

         ip_address() =:
           inet::ip_address

         subsystem_spec() =:
           {subsystem_name(), {channel_callback(), channel_init_args()}}

         subsystem_name() =:
           string()

         channel_callback() =:
           atom() - Name of the Erlang module implementing the subsystem using  the  ssh_channel  behavior,  see
           ssh_channel(3erl)

         key_cb() =:
           atom() | {atom(), list()}

           atom()   -   Name   of   the   erlang   module  implementing  the  behaviours  ssh_client_key_api  or
           ssh_client_key_api as the case maybe.

           list() - List of options that can be passed to the callback module.

         channel_init_args() =:
           list()

         algs_list() =:
           list( alg_entry() )

         alg_entry() =:
           {kex, simple_algs()} | {public_key, simple_algs()} | {cipher, double_algs()} | {mac, double_algs()} |
           {compression, double_algs()}

         simple_algs() =:
           list( atom() )

         double_algs() =:
           [{client2serverlist,simple_algs()},{server2client,simple_algs()}] | simple_algs()

         modify_algs_list() =:
           list( {append,algs_list()} | {prepend,algs_list()} | {rm,algs_list()} )

EXPORTS

       close(ConnectionRef) -> ok

              Types:

                 ConnectionRef = ssh_connection_ref()

              Closes an SSH connection.

       connect(Host, Port, Options) ->
       connect(Host, Port, Options, Timeout) ->
       connect(TcpSocket, Options) ->
       connect(TcpSocket, Options, Timeout) -> {ok, ssh_connection_ref()} | {error, Reason}

              Types:

                 Host = string()
                 Port = integer()
                   22 is default, the assigned well-known port number for SSH.
                 Options = [{Option, Value}]
                 Timeout = infinity | integer()
                   Negotiation  time-out  in  milli-seconds. The default value is infinity. For connection time-
                   out, use option {connect_timeout, timeout()}.
                 TcpSocket = port()
                   The  socket  is  supposed  to  be  from  gen_tcp:connect  or   gen_tcp:accept   with   option
                   {active,false}

              Connects   to   an   SSH   server.   No   channel   is   started.   This   is   done   by  calling
              ssh_connection:session_channel/[2, 4].

              Options:

                {inet, inet | inet6}:
                  IP version to use.

                {user_dir, string()}:
                  Sets the user directory, that is, the directory containing ssh  configuration  files  for  the
                  user,  such  as  known_hosts,  id_rsa,  id_dsa,  and authorized_key. Defaults to the directory
                  normally referred to as ~/.ssh.

                {dsa_pass_phrase, string()}:
                  If the user DSA key is protected by a passphrase, it can be supplied with this option.

                {rsa_pass_phrase, string()}:
                  If the user RSA key is protected by a passphrase, it can be supplied with this option.

                {ecdsa_pass_phrase, string()}:
                  If the user ECDSA key is protected by a passphrase, it can be supplied with this option.

                {silently_accept_hosts, boolean()}
                  {silently_accept_hosts, CallbackFun}
                  {silently_accept_hosts, {HashAlgoSpec, CallbackFun} }

                  HashAlgoSpec = crypto:digest_type() | [ crypto:digest_type() ]
                  CallbackFun = fun(PeerName, FingerPrint) -> boolean()
                  PeerName = string()
                  FingerPrint = string() | [ string() ] : This option guides the connect  function  how  to  act
                  when the connected server presents a Host Key that the client has not seen before. The default
                  is to ask the user with a question on stdio of whether to accept or reject the new  Host  Key.
                  See  also  the  option user_dir for the path to the file known_hosts where previously accepted
                  Host Keys are recorded.

                  The option can be given in three different forms as seen above:

                  * The value is a boolean(). The value true will make the client accept any  unknown  Host  Key
                    without  any user interaction. The value false keeps the default behaviour of asking the the
                    user on stdio.

                  * A CallbackFun will be called and the boolean return value true will make the  client  accept
                    the  Host  Key.  A  return  value  of  false will make the client to reject the Host Key and
                    therefore also the connection will be closed. The arguments to the fun are:

                    * PeerName - a string with the name or address of the remote host.

                    * FingerPrint - the fingerprint of  the  Host  Key  as  public_key:ssh_hostkey_fingerprint/1
                      calculates it.

                  * A  tuple  {HashAlgoSpec, CallbackFun}. The HashAlgoSpec specifies which hash algorithm shall
                    be used to calculate the fingerprint used in the call of the CallbackFun.  The  HashALgoSpec
                    is    either    an    atom    or    a   list   of   atoms   as   the   first   argument   in
                    public_key:ssh_hostkey_fingerprint/2.  If  it  is  a  list  of  hash  algorithm  names,  the
                    FingerPrint  argument in the CallbackFun will be a list of fingerprints in the same order as
                    the corresponding name in the HashAlgoSpec list.

                {user_interaction, boolean()}:
                  If false, disables the client to connect to the server if any user interaction is needed, such
                  as accepting the server to be added to the known_hosts file, or supplying a password. Defaults
                  to true. Even if user interaction is allowed it can be suppressed by other  options,  such  as
                  silently_accept_hosts  and  password.  However,  those options are not always desirable to use
                  from a security point of view.

                {disconnectfun, fun(Reason:term()) -> _}:
                  Provides a fun to implement your own logging when a server disconnects the client.

                {unexpectedfun, fun(Message:term(), Peer) -> report | skip }:
                  Provides a fun to implement your own logging  or  other  action  when  an  unexpected  message
                  arrives.  If the fun returns report the usual info report is issued but if skip is returned no
                  report is generated.

                  Peer is in the format of {Host,Port}.

                {pref_public_key_algs, list()}:
                  List of user (client) public key algorithms to try to use.

                  The default value is the public_key entry in ssh:default_algorithms/0.

                  If there is no public key of a specified type available, the corresponding entry  is  ignored.
                  Note that the available set is dependent on the underlying cryptolib and current user's public
                  keys.

                {preferred_algorithms, algs_list()}:
                  List of algorithms to use in  the  algorithm  negotiation.  The  default  algs_list()  can  be
                  obtained from default_algorithms/0.

                  If an alg_entry() is missing in the algs_list(), the default value is used for that entry.

                  Here is an example of this option:

                {preferred_algorithms,
                 [{public_key,['ssh-rsa','ssh-dss']},
                  {cipher,[{client2server,['aes128-ctr']},
                           {server2client,['aes128-cbc','3des-cbc']}]},
                  {mac,['hmac-sha2-256','hmac-sha1']},
                  {compression,[none,zlib]}
                  ]
                }

                  The   example  specifies  different  algorithms  in  the  two  directions  (client2server  and
                  server2client), for cipher but specifies the same algorithms for mac and compression  in  both
                  directions. The kex (key exchange) is implicit but public_key is set explicitly.

                  For background and more examples see the User's Guide.

            Warning:
                Changing  the  values  can  make a connection less secure. Do not change unless you know exactly
                what you are doing. If you do not understand the values then you  are  not  supposed  to  change
                them.

                {modify_algorithms, modify_algs_list()}:
                  Modifies  the  list  of  algorithms to use in the algorithm negotiation. The modifications are
                  applied after the option preferred_algorithms (if existing) is applied.

                  The algoritm for modifications works like this:

                  * Input  is  the  modify_algs_list()  and  a  set  of   algorithms   A   obtained   from   the
                    preferred_algorithms option if existing, or else from the ssh:default_algorithms/0.

                  * The head of the modify_algs_list() modifies A giving the result A'.

                    The possible modifications are:

                    * Append or prepend supported but not enabled algorithm(s) to the list of algorithms. If the
                      wanted algorithms already are in A they  will  first  be  removed  and  then  appended  or
                      prepended,

                    * Remove (rm) one or more algorithms from A.

                  * Repeat the modification step with the tail of modify_algs_list() and the resulting A'.

                  If an unsupported algorithm is in the modify_algs_list(), it will be silently ignored

                  If there are more than one modify_algorithms options, the result is undefined.

                  Here is an example of this option:

                {modify_algorithms,
                 [{prepend, [{kex, ['diffie-hellman-group1-sha1']}],
                  {rm,      [{compression, [none]}]}
                 ]
                }

                  The example specifies that:

                  * the  old key exchange algorithm 'diffie-hellman-group1-sha1' should be the main alternative.
                    It will be the main alternative since it is prepened to the list

                  * The compression algorithm none (= no compression) is removed so compression is enforced

                  For background and more examples see the User's Guide.

                {dh_gex_limits,{Min=integer(),I=integer(),Max=integer()}}:
                  Sets the three diffie-hellman-group-exchange parameters that guides the  connected  server  in
                  choosing  a  group. See RFC 4419 for the function of thoose. The default value is {1024, 6144,
                  8192}.

                {connect_timeout, timeout()}:
                  Sets a time-out on the transport layer connection. For gen_tcp the time  is  in  milli-seconds
                  and the default value is infinity.

                {auth_methods, string()}:
                  Comma-separated  string  that  determines  which  authentication methods that the client shall
                  support  and   in   which   order   they   are   tried.   Defaults   to   "publickey,keyboard-
                  interactive,password"

                {user, string()}:
                  Provides  a  username. If this option is not given, ssh reads from the environment (LOGNAME or
                  USER on UNIX, USERNAME on Windows).

                {password, string()}:
                  Provides a password for password authentication. If this option is  not  given,  the  user  is
                  asked for a password, if the password authentication method is attempted.

                {recv_ext_info, boolean()}:
                  Tell  the server that the client accepts extension negotiation. See Draft-ietf-curdle-ssh-ext-
                  info (work in progress) for details.

                  Currently implemented extension is server-sig-algs which is the list of the server's preferred
                  user's public key algorithms.

                  Default value is true.

                {key_cb, key_cb()}:
                  Module implementing the behaviour ssh_client_key_api. Can be used to customize the handling of
                  public keys. If callback options are provided along  with  the  module  name,  they  are  made
                  available to the callback module via the options passed to it under the key 'key_cb_private'.

                {quiet_mode, atom() = boolean()}:
                  If true, the client does not print anything on authorization.

                {id_string, random | string()}:
                  The  string  that  the  client  presents to a connected server initially. The default value is
                  "Erlang/VSN" where VSN is the ssh application version number.

                  The value random will cause a random string to be created at each connection attempt. This  is
                  to  make  it  a  bit  more  difficult  for a malicious peer to find the ssh software brand and
                  version.

                {fd, file_descriptor()}:
                  Allows an existing file descriptor to be used (by passing it on to the transport protocol).

                {rekey_limit, integer()}:
                  Provides, in bytes, when rekeying is to be initiated. Defaults to once per each  GB  and  once
                  per hour.

                {idle_time, integer()}:
                  Sets a time-out on a connection when no channels are active. Defaults to infinity.

                {ssh_msg_debug_fun,      fun(ConnectionRef::ssh_connection_ref(),      AlwaysDisplay::boolean(),
                Msg::binary(), LanguageTag::binary()) -> _}:
                  Provide a fun to implement your own logging of the SSH message SSH_MSG_DEBUG. The  last  three
                  parameters are from the message, see RFC4253, section 11.3. The ConnectionRef is the reference
                  to the connection on which the message arrived. The return value from the fun is not checked.

                  The default behaviour is ignore  the  message.  To  get  a  printout  for  each  message  with
                  AlwaysDisplay  = true, use for example {ssh_msg_debug_fun, fun(_,true,M,_)-> io:format("DEBUG:
                  ~p~n", [M]) end}

       connection_info(ConnectionRef, [Option]) ->[{Option, Value}]

              Types:

                 Option = client_version | server_version | user | peer | sockname
                 Value = [option_value()]
                 option_value()   =   {{Major::integer(),    Minor::integer()},    VersionString::string()}    |
                 User::string()    |   Peer::{inet:hostname(),   {inet::ip_adress(),   inet::port_number()}}   |
                 Sockname::{inet::ip_adress(), inet::port_number()}

              Retrieves information about a connection.

       daemon(Port) ->
       daemon(Port, Options) ->
       daemon(HostAddress, Port, Options) ->
       daemon(TcpSocket) ->
       daemon(TcpSocket, Options) -> {ok, ssh_daemon_ref()} | {error, atom()}

              Types:

                 Port = integer()
                 HostAddress = ip_address() | any | loopback
                 Options = [{Option, Value}]
                 Option = atom()
                 Value = term()
                 TcpSocket = port()
                   The  socket  is  supposed  to  be  from  gen_tcp:connect  or   gen_tcp:accept   with   option
                   {active,false}

              Starts  a  server listening for SSH connections on the given port. If the Port is 0, a random free
              port is selected. See daemon_info/1 about how to find the selected port number.

              Please note that by historical reasons both the HostAddress argument and the inet socket option ip
              set the listening address. This is a source of possible inconsistent settings.

              The rules for handling the two address passing options are:

                * if HostAddress is an IP-address, that IP-address is the listening address. An 'ip'-option will
                  be discarded if present.

                * if HostAddress is loopback, the listening address is loopback and an loopback address will  be
                  choosen by the underlying layers. An 'ip'-option will be discarded if present.

                * if  HostAddress  is  any  and  no 'ip'-option is present, the listening address is any and the
                  socket will listen to all addresses

                * if HostAddress is any and an 'ip'-option is present, the listening address is set to the value
                  of the 'ip'-option

              Options:

                {inet, inet | inet6}:
                  IP version to use when the host address is specified as any.

                {subsystems, [subsystem_spec()]}:
                  Provides  specifications  for  handling  of  subsystems. The "sftp" subsystem specification is
                  retrieved by calling ssh_sftpd:subsystem_spec/1. If the subsystems option is not present,  the
                  value  of  [ssh_sftpd:subsystem_spec([])]  is used. The option can be set to the empty list if
                  you do not want the daemon to run any subsystems.

                {shell, {Module, Function, Args} | fun(string() =  User)  -  >  pid()  |  fun(string()  =  User,
                ip_address() = PeerAddr) -> pid()}:
                  Defines  the read-eval-print loop used when a shell is requested by the client. The default is
                  to use the Erlang shell: {shell, start, []}

                {ssh_cli, {channel_callback(), channel_init_args()} | no_cli}:
                  Provides your own CLI implementation, that is, a channel callback  module  that  implements  a
                  shell  and  command  execution.  The  shell  read-eval-print loop can be customized, using the
                  option shell. This means less work than implementing an own CLI channel. If set to no_cli, the
                  CLI channels are disabled and only subsystem channels are allowed.

                {user_dir, string()}:
                  Sets  the  user  directory.  That is, the directory containing ssh configuration files for the
                  user, such as known_hosts, id_rsa, id_dsa,  and  authorized_key.  Defaults  to  the  directory
                  normally referred to as ~/.ssh.

                {system_dir, string()}:
                  Sets  the system directory, containing the host key files that identify the host keys for ssh.
                  Defaults to /etc/ssh. For security reasons, this directory is normally accessible only to  the
                  root user.

                {auth_methods, string()}:
                  Comma-separated  string  that  determines  which  authentication methods that the server is to
                  support   and   in   what   order   they   are   tried.   Defaults   to   "publickey,keyboard-
                  interactive,password"

                  Note that the client is free to use any order and to exclude methods.

                {auth_method_kb_interactive_data, PromptTexts}
                  where:
                  PromptTexts   =   kb_int_tuple()  |  fun(Peer::{IP::tuple(),Port::integer()},  User::string(),
                  Service::string()) -> kb_int_tuple()
                  kb_int_tuple() = {Name::string(), Instruction::string(),  Prompt::string(),  Echo::boolean()}:
                  Sets  the  text  strings that the daemon sends to the client for presentation to the user when
                  using keyboar-interactive authentication. If the fun/3 is used, it is called when  the  actual
                  authentication occurs and may therefore return dynamic data like time, remote ip etc.

                  The parameter Echo guides the client about need to hide the password.

                  The  default  value  is:  {auth_method_kb_interactive_data, {"SSH server", "Enter password for
                  \""++User++"\"", "password: ", false}>

                {user_passwords, [{string() = User, string() = Password}]}:
                  Provides passwords for password authentication. The passwords are used when someone  tries  to
                  connect  to the server and public key user-authentication fails. The option provides a list of
                  valid usernames and the corresponding passwords.

                {password, string()}:
                  Provides a global password that authenticates any  user.  From  a  security  perspective  this
                  option makes the server very vulnerable.

                {preferred_algorithms, algs_list()}:
                  List  of  algorithms  to  use  in  the  algorithm  negotiation. The default algs_list() can be
                  obtained from default_algorithms/0.

                  If an alg_entry() is missing in the algs_list(), the default value is used for that entry.

                  Here is an example of this option:

                {preferred_algorithms,
                 [{public_key,['ssh-rsa','ssh-dss']},
                  {cipher,[{client2server,['aes128-ctr']},
                           {server2client,['aes128-cbc','3des-cbc']}]},
                  {mac,['hmac-sha2-256','hmac-sha1']},
                  {compression,[none,zlib]}
                  ]
                }

                  The  example  specifies  different  algorithms  in  the  two  directions  (client2server   and
                  server2client),  for  cipher but specifies the same algorithms for mac and compression in both
                  directions. The kex (key exchange) is implicit but public_key is set explicitly.

                  For background and more examples see the User's Guide.

            Warning:
                Changing the values can make a connection less secure. Do not change  unless  you  know  exactly
                what  you  are  doing.  If  you do not understand the values then you are not supposed to change
                them.

                {modify_algorithms, modify_algs_list()}:
                  Modifies the list of algorithms to use in the algorithm  negotiation.  The  modifications  are
                  applied after the option preferred_algorithms is applied (if existing)

                  The possible modifications are to:

                  * Append or prepend supported but not enabled algorithm(s) to the list of algorithms.

                    If  the  wanted algorithms already are in the list of algorithms, they will first be removed
                    and then appended or prepended.

                  * Remove (rm) one or more algorithms from the list of algorithms.

                  If an unsupported algorithm is in the list, it will be silently ignored

                  Here is an example of this option:

                {modify_algorithms,
                 [{prepend, [{kex, ['diffie-hellman-group1-sha1']}],
                  {rm,      [{compression, [none]}]}
                 ]
                }

                  The example specifies that:

                  * the old key exchange algorithm 'diffie-hellman-group1-sha1' should be the main  alternative.
                    It will be the main alternative since it is prepened to the list

                  * The compression algorithm none (= no compression) is removed so compression is enforced

                  For background and more examples see the User's Guide.

                {dh_gex_groups,       [{Size=integer(),G=integer(),P=integer()}]       |       {file,filename()}
                {ssh_moduli_file,filename()} }:
                  Defines  the  groups  the  server  may  choose  among  when  diffie-hellman-group-exchange  is
                  negotiated. See RFC 4419 for details. The three variants of this option are:

                  {Size=integer(),G=integer(),P=integer()}:
                    The  groups  are  given explicitly in this list. There may be several elements with the same
                    Size. In such a case, the server will choose one randomly in the negotiated Size.

                  {file,filename()}:
                    The  file  must  have  one  or  more  three-tuples  {Size=integer(),G=integer(),P=integer()}
                    terminated by a dot. The file is read when the daemon starts.

                  {ssh_moduli_file,filename()}:
                    The file must be in ssh-keygen moduli file format. The file is read when the daemon starts.

                  The default list is fetched from the public_key application.

                {dh_gex_limits,{Min=integer(),Max=integer()}}:
                  Limits what a client can ask for in diffie-hellman-group-exchange. The limits will be {MaxUsed
                  = min(MaxClient,Max), MinUsed = max(MinClient,Min)} where  MaxClient  and  MinClient  are  the
                  values proposed by a connecting client.

                  The default value is {0,infinity}.

                  If MaxUsed < MinUsed in a key exchange, it will fail with a disconnect.

                  See RFC 4419 for the function of the Max and Min values.

                {pwdfun,   fun(User::string(),   Password::string(),   PeerAddress::{ip_adress(),port_number()},
                State::any()) -> boolean() | disconnect | {boolean(),any()} }:
                  Provides a function for password validation. This could used for calling an external system or
                  if passwords should be stored as a hash. The fun returns:

                  * true if the user and password is valid and

                  * false otherwise.

                  This  fun  can  also  be  used  to  make delays in authentication tries for example by calling
                  timer:sleep/1. To facilitate counting of failed tries the State variable could be  used.  This
                  state  is per connection only. The first time the pwdfun is called for a connection, the State
                  variable has the value undefined. The pwdfun can return - in addition to the values above -  a
                  new state as:

                  * {true, NewState:any()} if the user and password is valid or

                  * {false, NewState:any()} if the user or password is invalid

                  A  third  usage is to block login attempts from a missbehaving peer. The State described above
                  can be used for this. In addition to the  responses  above,  the  following  return  value  is
                  introduced:

                  * disconnect if the connection should be closed immediately after sending a SSH_MSG_DISCONNECT
                    message.

                {pwdfun, fun(User::string(), Password::string()) -> boolean()}:
                  Provides a function for password validation. This function is called with user and password as
                  strings, and returns true if the password is valid and false otherwise.

                  This  option  ({pwdfun,fun/2}) is the same as a subset of the previous ({pwdfun,fun/4}). It is
                  kept for compatibility.

                {negotiation_timeout, integer()}:
                  Maximum time in milliseconds  for  the  authentication  negotiation.  Defaults  to  120000  (2
                  minutes). If the client fails to log in within this time, the connection is closed.

                {max_sessions, pos_integer()}:
                  The  maximum  number  of  simultaneous sessions that are accepted at any time for this daemon.
                  This includes sessions that are being authorized. Thus, if  set  to  N,  and  N  clients  have
                  connected  but  not  started  the  login  process,  connection  attempt  N+1  is aborted. If N
                  connections are authenticated and still logged in, no more logins are accepted  until  one  of
                  the existing ones log out.

                  The counter is per listening port. Thus, if two daemons are started, one with {max_sessions,N}
                  and the other with {max_sessions,M}, in total N+M connections are accepted for the  whole  ssh
                  application.

                  Notice that if parallel_login is false, only one client at a time can be in the authentication
                  phase.

                  By default, this option is not set. This means that the number is not limited.

                {max_channels, pos_integer()}:
                  The maximum number of channels with  active  remote  subsystem  that  are  accepted  for  each
                  connection to this daemon

                  By default, this option is not set. This means that the number is not limited.

                {parallel_login, boolean()}:
                  If  set  to false (the default value), only one login is handled at a time. If set to true, an
                  unlimited number of login attempts are allowed simultaneously.

                  If the max_sessions option is set to N and parallel_login is set to true, the  maximum  number
                  of  simultaneous  login  attempts  at  any  time  is  limited to N-K, where K is the number of
                  authenticated connections present at this daemon.

            Warning:
                Do not enable parallel_logins without protecting the server by other means, for example, by  the
                max_sessions  option or a firewall configuration. If set to true, there is no protection against
                DOS attacks.

                {minimal_remote_max_packet_size, non_negative_integer()}:
                  The least maximum packet size that the daemon will accept in channel open  requests  from  the
                  client. The default value is 0.

                {id_string, random | string()}:
                  The  string  the  daemon  will  present  to  a connecting peer initially. The default value is
                  "Erlang/VSN" where VSN is the ssh application version number.

                  The value random will cause a random string to be created at each connection attempt. This  is
                  to  make  it  a  bit  more  difficult  for a malicious peer to find the ssh software brand and
                  version.

                {send_ext_info, boolean()}:
                  Send a list of extensions to the client if the client has asked for it. See Draft-ietf-curdle-
                  ssh-ext-info (work in progress) for details.

                  Currently  implemented  extension is sending server-sig-algs which is the list of the server's
                  preferred user's public key algorithms.

                  Default value is true.

                {key_cb, key_cb()}:
                  Module implementing the behaviour ssh_server_key_api. Can be used to customize the handling of
                  public  keys.  If  callback  options  are  provided  along with the module name, they are made
                  available to the callback module via the options passed to it under the key 'key_cb_private'.

                {profile, atom()}:
                  Used together with ip-address and port to uniquely identify a ssh daemon. This can  be  useful
                  in  a  virtualized  environment, where there can be more that one server that has the same ip-
                  address and port. If this property is not explicitly set, it  is  assumed  that  the  the  ip-
                  address and port uniquely identifies the SSH daemon.

                {fd, file_descriptor()}:
                  Allows an existing file-descriptor to be used (passed on to the transport protocol).

                {failfun, fun(User::string(), PeerAddress::ip_address(), Reason::term()) -> _}:
                  Provides a fun to implement your own logging when a user fails to authenticate.

                {connectfun, fun(User::string(), PeerAddress::ip_address(), Method::string()) ->_}:
                  Provides a fun to implement your own logging when a user authenticates to the server.

                {disconnectfun, fun(Reason:term()) -> _}:
                  Provides a fun to implement your own logging when a user disconnects from the server.

                {unexpectedfun, fun(Message:term(), Peer) -> report | skip }:
                  Provides  a  fun  to  implement  your  own  logging or other action when an unexpected message
                  arrives. If the fun returns report the usual info report is issued but if skip is returned  no
                  report is generated.

                  Peer is in the format of {Host,Port}.

                {idle_time, integer()}:
                  Sets a time-out on a connection when no channels are active. Defaults to infinity.

                {ssh_msg_debug_fun,      fun(ConnectionRef::ssh_connection_ref(),      AlwaysDisplay::boolean(),
                Msg::binary(), LanguageTag::binary()) -> _}:
                  Provide a fun to implement your own logging of the SSH message SSH_MSG_DEBUG. The  last  three
                  parameters are from the message, see RFC4253, section 11.3. The ConnectionRef is the reference
                  to the connection on which the message arrived. The return value from the fun is not checked.

                  The default behaviour is ignore  the  message.  To  get  a  printout  for  each  message  with
                  AlwaysDisplay  = true, use for example {ssh_msg_debug_fun, fun(_,true,M,_)-> io:format("DEBUG:
                  ~p~n", [M]) end}

       daemon_info(Daemon) -> {ok, [DaemonInfo]} | {error,Error}

              Types:

                 DaemonInfo = {port,Port::pos_integer()} | {listen_address, any|ip_address()} | {profile,atom()}
                 Port = integer()
                 Error = bad_daemon_ref

              Returns a key-value list with information about the daemon. For now, only the  listening  port  is
              returned. This is intended for the case the daemon is started with the port set to 0.

       default_algorithms() -> algs_list()

              Returns  a key-value list, where the keys are the different types of algorithms and the values are
              the algorithms themselves. An example:

              20> ssh:default_algorithms().
              [{kex,['diffie-hellman-group1-sha1']},
               {public_key,['ssh-rsa','ssh-dss']},
               {cipher,[{client2server,['aes128-ctr','aes128-cbc','3des-cbc']},
                        {server2client,['aes128-ctr','aes128-cbc','3des-cbc']}]},
               {mac,[{client2server,['hmac-sha2-256','hmac-sha1']},
                     {server2client,['hmac-sha2-256','hmac-sha1']}]},
               {compression,[{client2server,[none,zlib]},
                             {server2client,[none,zlib]}]}]
              21>

       shell(Host) ->
       shell(Host, Option) ->
       shell(Host, Port, Option) ->
       shell(TcpSocket) -> _

              Types:

                 Host = string()
                 Port = integer()
                 Options - see ssh:connect/3
                 TcpSocket = port()
                   The  socket  is  supposed  to  be  from  gen_tcp:connect  or   gen_tcp:accept   with   option
                   {active,false}

              Starts  an  interactive  shell  over  an SSH server on the given Host. The function waits for user
              input, and does not return until the remote shell is ended (that is, exit from the shell).

       start() ->
       start(Type) -> ok | {error, Reason}

              Types:

                 Type = permanent | transient | temporary
                 Reason = term()

              Utility function that starts the  applications  crypto,  public_key,  and  ssh.  Default  type  is
              temporary. For more information, see the application(3erl) manual page in Kernel.

       stop() -> ok | {error, Reason}

              Types:

                 Reason = term()

              Stops the ssh application. For more information, see the application(3erl) manual page in Kernel.

       stop_daemon(DaemonRef) ->
       stop_daemon(Address, Port) -> ok

              Types:

                 DaemonRef = ssh_daemon_ref()
                 Address = ip_address()
                 Port = integer()

              Stops the listener and all connections started by the listener.

       stop_listener(DaemonRef) ->
       stop_listener(Address, Port) -> ok

              Types:

                 DaemonRef = ssh_daemon_ref()
                 Address = ip_address()
                 Port = integer()

              Stops the listener, but leaves existing connections started by the listener operational.