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SSH(7)			 Erlang	Application Definition			SSH(7)

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 han-
       dle 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 configura-
       tion file, as described in application(3). 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.

       See also	the default callback module documentation in ssh_file.

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 pub-
       lic  keys. Once a server	is listed, it can be verified without user in-
       teraction.

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, DSA	and ECDSA 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 options preferred_algorithms and mod-
       ify_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

	   * diffie-hellman-group14-sha1

	   * diffie-hellman-group-exchange-sha1

	   * (diffie-hellman-group1-sha1, retired: It can be enabled with  the
	     preferred_algorithms or modify_algorithms options)

	 Public	key algorithms:

	   * ecdsa-sha2-nistp384

	   * ecdsa-sha2-nistp521

	   * ecdsa-sha2-nistp256

	   * ssh-ed25519

	   * ssh-ed448

	   * ssh-rsa

	   * rsa-sha2-256

	   * rsa-sha2-512

	   * ssh-dss

	 MAC algorithms:

	   * hmac-sha2-256

	   * hmac-sha2-512

	   * hmac-sha1

	 Encryption algorithms (ciphers):

	   * chacha20-poly1305@openssh.com

	   * aes256-gcm@openssh.com

	   * aes256-ctr

	   * aes192-ctr

	   * aes128-gcm@openssh.com

	   * aes128-ctr

	   * 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	 algo-
	   rithm    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. Disabled by default, can be  en-
	     abled with	the preferred_algorithms or modify_algorithms options.

	 * 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	imple-
	   mented.  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 re-
	 sponsibility to check that other implementation has the  same	inter-
	 pretation  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 ap-
	   plied

	 * 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:

	   * The  diffie-hellman-group1-sha1 is	not enabled by default,	but is
	     still supported and can be	enabled	with the options preferred_al-
	     gorithms or modify_algorithms.

	   * The  questionable	sha1-based algorithms diffie-hellman-group-ex-
	     change-sha1 and diffie-hellman-group14-sha1 are still enabled  by
	     default  for compatibility	with ancient clients and servers. They
	     can be disabled with the  options	preferred_algorithms  or  mod-
	     ify_algorithms.  They  will be disabled by	default	when the draft
	     is	turned into an RFC.

	 * 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 (work in progress)

	 * Ed25519 and Ed448 public key	algorithms for the Secure Shell	 (SSH)
	   protocol (work in progress)

SEE ALSO
       application(3)

Ericsson AB			   ssh 4.7.4				SSH(7)

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

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