Provided by: erlang-manpages_24.2.1+dfsg-1ubuntu0.1_all bug

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. The call  ssh:start/0  will  do
       the necessary calls to application:start/1,2 before it starts the ssh itself.

CONFIGURATION

       The SSH application uses Configuration Parameters. Where to set them are described in config User's Guide
       with SSH details in Configuration in SSH.

       Some special configuration files from OpenSSH are also used:

         * known_hosts

         * authorized_keys

         * authorized_keys2

         * id_dsa(supported but disabled by default)

         * id_rsa(SHA1 sign/verify are supported but disabled by default from OTP-24)

         * id_ecdsa

         * id_ed25519

         * id_ed448

         * ssh_host_dsa_key(supported but disabled by default)

         * ssh_host_rsa_key(SHA1 sign/verify are supported but disabled by default from OTP-24)

         * ssh_host_ecdsa_key

         * ssh_host_ed25519_key

         * ssh_host_ed448_key

       By default, ssh looks for id_*, known_hosts, and authorized_keys in ~/.ssh, and  for  the  ssh_host_*_key
       files  in  /etc/ssh.  These  locations  can be changed by the options user_dir and system_dir. More about
       where to set them is described in Configuration in SSH.

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

       See also the default callback module documentation in ssh_file.

       Disabled public key algorithms can be enabled with the preferred_algorithms or modify_algorithms options.
       See Example 9 in Configuring algorithms in SSH for a description.

PUBLIC KEYS

       id_* 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.

       See ssh_file for details.

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.

       See ssh_file for details.

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.

       See ssh_file for details.

HOST KEYS

       RSA, DSA (if enabled), ECDSA, ED25519 and ED448 host keys are supported and are expected to be  found  in
       files    named   ssh_host_rsa_key,   ssh_host_dsa_key,   ssh_host_ecdsa_key,   ssh_host_ed25519_key   and
       ssh_host_ed448_key.

       See ssh_file for details.

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
       options preferred_algorithms and modify_algorithms in the ssh:daemon/1,2,3 and ssh:connect/3,4 functions.

       Supported algorithms are (in the default order):

         Key exchange algorithms:

           * ecdh-sha2-nistp384

           * ecdh-sha2-nistp521

           * ecdh-sha2-nistp256

           * diffie-hellman-group-exchange-sha256

           * diffie-hellman-group16-sha512

           * diffie-hellman-group18-sha512

           * diffie-hellman-group14-sha256

           * curve25519-sha256

           * curve25519-sha256@libssh.org

           * curve448-sha512

           The following unsecure SHA1 algorithms are now disabled by default:

           * (diffie-hellman-group14-sha1)

           * (diffie-hellman-group-exchange-sha1)

           * (diffie-hellman-group1-sha1)

           They can be enabled with the preferred_algorithms or modify_algorithms options. Use for  example  the
           Option value {modify_algorithms, [{append, [{kex,['diffie-hellman-group1-sha1']}]}]})

         Public key algorithms:

           * ecdsa-sha2-nistp384

           * ecdsa-sha2-nistp521

           * ecdsa-sha2-nistp256

           * ssh-ed25519

           * ssh-ed448

           * rsa-sha2-256

           * rsa-sha2-512

           The following unsecure SHA1 algorithms are supported but disabled by default:

           * (ssh-dss)

           * (ssh-rsa)

           See  Disabled public key algorithms can be enabled with the preferred_algorithms or modify_algorithms
           options. See Example 9 in Configuring algorithms in SSH for a description.

         MAC algorithms:

           * hmac-sha2-256-etm@openssh.com

           * hmac-sha2-512-etm@openssh.com

           * hmac-sha1-etm@openssh.com

           * hmac-sha2-256

           * hmac-sha2-512

           * hmac-sha1

           The following unsecure SHA1 algorithm is disabled by default:

           * (hmac-sha1-96)

           It can be enabled with the preferred_algorithms or modify_algorithms options.  Use  for  example  the
           Option value {modify_algorithms, [{append, [{mac,['hmac-sha1-96']}]}]})

         Encryption algorithms (ciphers):

           * chacha20-poly1305@openssh.com

           * aes256-gcm@openssh.com

           * aes256-ctr

           * aes192-ctr

           * aes128-gcm@openssh.com

           * aes128-ctr

           * aes256-cbc

           * aes192-cbc

           * aes128-cbc

           * 3des-cbc

           * (AEAD_AES_128_GCM, not enabled per default)

           * (AEAD_AES_256_GCM, not enabled per default)

           See  the  text  at  the  description  of  the  rfc  5647  further down for more information regarding
           AEAD_AES_*_GCM.

           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.

         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.

           Except

           * 8.1. diffie-hellman-group1-sha1

           * 6.6. Public Key Algorithms

             * ssh-dss

             * ssh-rsa

           They  are  disabled  by  default  as they now are regarded insecure, but they can be enabled with the
           preferred_algorithms or modify_algorithms options. See  Example  8  (diffie-hellman-group1-sha1)  and
           Example 9 (ssh-dss) in Configuring algorithms in SSH for descriptions.

         * 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.

           Except

           * 4.1. diffie-hellman-group-exchange-sha1

           It  is  disabled  by  defaultas  as  it  now  is  regarded  insecure,  but it can be enabled with the
           preferred_algorithms or modify_algorithms options.

         * 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 options preferred_algorithms or modify_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

         * Draft-ietf-curdle-ssh-kex-sha2   (work   in   progress),   Key  Exchange  (KEX)  Method  Updates  and
           Recommendations for Secure Shell (SSH).

           Deviations:

           * diffie-hellman-group1-sha1

           * diffie-hellman-group-exchange-sha1

           * diffie-hellman-group14-sha1

           are not enabled by default as they now are regarded insecure, but are  still  supported  and  can  be
           enabled with the options preferred_algorithms or modify_algorithms.

         * RFC 8332, Use of RSA Keys with SHA-256 and SHA-512 in the Secure Shell (SSH) Protocol.

         * RFC 8308, Extension Negotiation in the Secure Shell (SSH) Protocol.

           Implemented are:

           * The Extension Negotiation Mechanism

           * The extension server-sig-algs

         * Secure Shell (SSH) Key Exchange Method Using Curve25519 and Curve448

         * RFC 8709 Ed25519 and Ed448 public key algorithms for the Secure Shell (SSH) protocol

SEE ALSO

       application(3erl)