Ubuntu Manpage: SSH - The ssh application implements the Secure Shell (SSH) protocol and

Provided by: erlang-manpages_18.3-dfsg-1ubuntu3.1_all

NAME

       SSH - The ssh application implements the Secure Shell (SSH) protocol and
         provides an SSH File Transfer Protocol (SFTP) client and server.

DESCRIPTION

       The  ssh  application  is  an implementation of the SSH protocol in Erlang. ssh offers API
       functions to write customized SSH clients and servers as well as making the  Erlang  shell
       available over SSH. An SFTP client, ssh_sftp, and server, ssh_sftpd, are also included.

DEPENDENCIES

       The  ssh application uses the applications public_key and crypto to handle public keys and
       encryption. Hence, these applications must be loaded for the ssh application to  work.  In
       an  embedded  environment  this means that they must be started with application:start/1,2
       before the ssh application is started.

CONFIGURATION

       The ssh application  does  not  have  an  application-  specific  configuration  file,  as
       described  in  application(3erl).  However,  by default it use the following configuration
       files from OpenSSH:

         * known_hosts

         * authorized_keys

         * authorized_keys2

         * id_dsa

         * id_rsa

         * id_ecdsa

         * ssh_host_dsa_key

         * ssh_host_rsa_key

         * ssh_host_ecdsa_key

       By default, ssh looks for id_dsa, id_rsa, id_ecdsa_key, known_hosts,  and  authorized_keys
       in  ~/.ssh,  and for the host key files in /etc/ssh. These locations can be changed by the
       options user_dir and system_dir.

       Public key handling can also be customized through a callback module that  implements  the
       behaviors ssh_client_key_api and ssh_server_key_api.

PUBLIC KEYS

       id_dsa, id_rsa and id_ecdsa are the users private key files. Notice that the public key is
       part of the private key so the ssh application does not use the  id_<*>.pub  files.  These
       are for the user's convenience when it is needed to convey the user's public key.

KNOWN HOSTS

       The  known_hosts  file  contains  a list of approved servers and their public keys. Once a
       server is listed, it can be verified without user interaction.

AUTHORIZED KEYS

       The authorized_key file keeps track of the user's authorized public keys. The most  common
       use  of  this  file  is  to  let  users  log  in without entering their password, which is
       supported by the Erlang ssh daemon.

HOST KEYS

       RSA and DSA host keys  are  supported  and  are  expected  to  be  found  in  files  named
       ssh_host_rsa_key, ssh_host_dsa_key and ssh_host_ecdsa_key.

ERROR LOGGER AND EVENT HANDLERS

       The  ssh  application  uses the default OTP error logger to log unexpected errors or print
       information about special events.

SUPPORTED SPECIFICATIONS AND STANDARDS

       The supported SSH version is 2.0.

ALGORITHMS

       The actual set of algorithms may vary depending on which OpenSSL crypto  library  that  is
       installed  on  the  machine.  For  the  list on a particular installation, use the command
       ssh:default_algorithms/0. The user may override the default algorithm  configuration  both
       on  the  server  side  and  the  client  side.  See the option preferred_algorithms in the
       ssh:daemon/1,2,3 and ssh:connect/3,4 functions.

       Supported algorithms are:

         Key exchange algorithms:

           * ecdh-sha2-nistp256

           * ecdh-sha2-nistp384

           * ecdh-sha2-nistp521

           * diffie-hellman-group-exchange-sha1

           * diffie-hellman-group-exchange-sha256

           * diffie-hellman-group14-sha1

           * diffie-hellman-group1-sha1

         Public key algorithms:

           * ecdsa-sha2-nistp256

           * ecdsa-sha2-nistp384

           * ecdsa-sha2-nistp521

           * ssh-rsa

           * ssh-dss

         MAC algorithms:

           * hmac-sha2-256

           * hmac-sha2-512

           * hmac-sha1

         Encryption algorithms (ciphers):

           * aes128-gcm@openssh.com (AEAD_AES_128_GCM)

           * aes256-gcm@openssh.com (AEAD_AES_256_GCM)

           * aes128-ctr

           * aes192-ctr

           * aes256-ctr

           * aes128-cbc

           * 3des-cbc

           Following  the  internet   de-facto   standard,   the   cipher   and   mac   algorithm
           AEAD_AES_128_GCM is selected when the cipher aes128-gcm@openssh.com is negotiated. The
           cipher  and   mac   algorithm   AEAD_AES_256_GCM   is   selected   when   the   cipher
           aes256-gcm@openssh.com is negotiated.

           See the text at the description of the rfc 5647 further down for more information.

         Compression algorithms:

           * none

           * zlib@openssh.com

           * zlib

UNICODE SUPPORT

       Unicode  filenames  are  supported  if the emulator and the underlaying OS support it. See
       section DESCRIPTION in the file manual page in kernel for information about this subject.

       The shell and the cli both support unicode.

RFCS

The following rfc:s are supported:

* RFC 4251, The Secure Shell (SSH) Protocol Architecture.

Except

* 9.4.6 Host-Based Authentication

* 9.5.2 Proxy Forwarding

* 9.5.3 X11 Forwarding

* RFC 4252, The Secure Shell (SSH) Authentication Protocol.

Except

* 9. Host-Based Authentication: "hostbased"

* RFC 4253, The Secure Shell (SSH) Transport Layer Protocol.

* RFC 4254, The Secure Shell (SSH) Connection Protocol.

Except

* 6.3. X11 Forwarding

* 7. TCP/IP Port Forwarding

* RFC 4256, Generic Message Exchange Authentication for the Secure Shell Protocol (SSH).

Except

* num-prompts > 1

* password changing

* other identification methods than userid-password

* RFC 4419, Diffie-Hellman Group Exchange for the Secure Shell (SSH) Transport Layer
Protocol.

* RFC 4716, The Secure Shell (SSH) Public Key File Format.

* RFC 5647, AES Galois Counter Mode for the Secure Shell Transport Layer Protocol.

There is an ambiguity in the synchronized selection of cipher and mac algorithm. This
is resolved by OpenSSH in the ciphers aes128-gcm@openssh.com and
aes256-gcm@openssh.com which are implemented. If the explicit ciphers and macs
AEAD_AES_128_GCM or AEAD_AES_256_GCM are needed, they could be enabled with the option
preferred_algorithms.

Warning:
If the client or the server is not Erlang/OTP, it is the users responsibility to check
that other implementation has the same interpretation of AEAD_AES_*_GCM as the
Erlang/OTP SSH before enabling them. The aes*-gcm@openssh.com variants are always safe
to use since they lack the ambiguity.

The second paragraph in section 5.1 is resolved as:

* If the negotiated cipher is AEAD_AES_128_GCM, the mac algorithm is set to
AEAD_AES_128_GCM.

* If the negotiated cipher is AEAD_AES_256_GCM, the mac algorithm is set to
AEAD_AES_256_GCM.

* If the mac algorithm is AEAD_AES_128_GCM, the cipher is set to AEAD_AES_128_GCM.

* If the mac algorithm is AEAD_AES_256_GCM, the cipher is set to AEAD_AES_256_GCM.

The first rule that matches when read in order from the top is applied

* RFC 5656, Elliptic Curve Algorithm Integration in the Secure Shell Transport Layer.

Except

* 5. ECMQV Key Exchange

* 6.4. ECMQV Key Exchange and Verification Method Name

* 7.2. ECMQV Message Numbers

* 10.2. Recommended Curves

* RFC 6668, SHA-2 Data Integrity Verification for the Secure Shell (SSH) Transport Layer
Protocol

Comment: Defines hmac-sha2-256 and hmac-sha2-512

NAME

DESCRIPTION

DEPENDENCIES

CONFIGURATION

PUBLIC KEYS

KNOWN HOSTS

AUTHORIZED KEYS

HOST KEYS

ERROR LOGGER AND EVENT HANDLERS

SUPPORTED SPECIFICATIONS AND STANDARDS

ALGORITHMS

UNICODE SUPPORT

RFCS

SEE ALSO