view dropbear.8 @ 1672:3a97f14c0235

Add Chacha20-Poly1305, AES128-GCM and AES256-GCM support (#93) * Add Chacha20-Poly1305 authenticated encryption * Add general AEAD approach. * Add [email protected] algo using LibTomCrypt chacha and poly1305 routines. Chacha20-Poly1305 is generally faster than AES256 on CPU w/o dedicated AES instructions, having the same key size. Compiling in will add ~5,5kB to binary size on x86-64. function old new delta chacha_crypt - 1397 +1397 _poly1305_block - 608 +608 poly1305_done - 595 +595 dropbear_chachapoly_crypt - 457 +457 .rodata 26976 27392 +416 poly1305_process - 290 +290 poly1305_init - 221 +221 chacha_setup - 218 +218 encrypt_packet 1068 1270 +202 dropbear_chachapoly_getlength - 147 +147 decrypt_packet 756 897 +141 chacha_ivctr64 - 137 +137 read_packet 543 637 +94 dropbear_chachapoly_start - 94 +94 read_kex_algos 792 880 +88 chacha_keystream - 69 +69 dropbear_mode_chachapoly - 48 +48 sshciphers 280 320 +40 dropbear_mode_none 24 48 +24 dropbear_mode_ctr 24 48 +24 dropbear_mode_cbc 24 48 +24 dropbear_chachapoly_mac - 24 +24 dropbear_chachapoly - 24 +24 gen_new_keys 848 854 +6 ------------------------------------------------------------------------------ (add/remove: 14/0 grow/shrink: 10/0 up/down: 5388/0) Total: 5388 bytes * Add AES128-GCM and AES256-GCM authenticated encryption * Add general AES-GCM mode. * Add [email protected] and [email protected] algo using LibTomCrypt gcm routines. AES-GCM is combination of AES CTR mode and GHASH, slower than AES-CTR on CPU w/o dedicated AES/GHASH instructions therefore disabled by default. Compiling in will add ~6kB to binary size on x86-64. function old new delta gcm_process - 1060 +1060 .rodata 26976 27808 +832 gcm_gf_mult - 820 +820 gcm_add_aad - 660 +660 gcm_shift_table - 512 +512 gcm_done - 471 +471 gcm_add_iv - 384 +384 gcm_init - 347 +347 dropbear_gcm_crypt - 309 +309 encrypt_packet 1068 1270 +202 decrypt_packet 756 897 +141 gcm_reset - 118 +118 read_packet 543 637 +94 read_kex_algos 792 880 +88 sshciphers 280 360 +80 gcm_mult_h - 80 +80 dropbear_gcm_start - 62 +62 dropbear_mode_gcm - 48 +48 dropbear_mode_none 24 48 +24 dropbear_mode_ctr 24 48 +24 dropbear_mode_cbc 24 48 +24 dropbear_ghash - 24 +24 dropbear_gcm_getlength - 24 +24 gen_new_keys 848 854 +6 ------------------------------------------------------------------------------ (add/remove: 14/0 grow/shrink: 10/0 up/down: 6434/0) Total: 6434 bytes
author Vladislav Grishenko <themiron@users.noreply.github.com>
date Mon, 25 May 2020 20:50:25 +0500
parents d32bcb5c557d
children 94323a20e572
line wrap: on
line source

.TH dropbear 8
.SH NAME
dropbear \- lightweight SSH server
.SH SYNOPSIS
.B dropbear
[\fIflag arguments\fR] [\-b
.I banner\fR] 
[\-r
.I hostkeyfile\fR] [\-p [\fIaddress\fR:]\fIport\fR]
.SH DESCRIPTION
.B dropbear
is a small SSH server 
.SH OPTIONS
.TP
.B \-b \fIbanner
bannerfile.
Display the contents of the file
.I banner
before user login (default: none).
.TP
.B \-r \fIhostkey
Use the contents of the file
.I hostkey
for the SSH hostkey.
This file is generated with
.BR dropbearkey (1) 
or automatically with the '-R' option. See "Host Key Files" below.
.TP
.B \-R
Generate hostkeys automatically. See "Host Key Files" below.
.TP
.B \-F
Don't fork into background.
.TP
.B \-E
Log to standard error rather than syslog.
.TP
.B \-m
Don't display the message of the day on login.
.TP
.B \-w
Disallow root logins.
.TP
.B \-s
Disable password logins.
.TP
.B \-g
Disable password logins for root.
.TP
.B \-j
Disable local port forwarding.
.TP
.B \-k
Disable remote port forwarding.
.TP
.B \-p\fR [\fIaddress\fR:]\fIport
Listen on specified 
.I address
and TCP
.I port.
If just a port is given listen
on all addresses.
up to 10 can be specified (default 22 if none specified).
.TP
.B \-i
Service program mode.
Use this option to run
.B dropbear
under TCP/IP servers like inetd, tcpsvd, or tcpserver.
In program mode the \-F option is implied, and \-p options are ignored.
.TP
.B \-P \fIpidfile
Specify a pidfile to create when running as a daemon. If not specified, the 
default is /var/run/dropbear.pid
.TP
.B \-a
Allow remote hosts to connect to forwarded ports.
.TP
.B \-W \fIwindowsize
Specify the per-channel receive window buffer size. Increasing this 
may improve network performance at the expense of memory use. Use -h to see the
default buffer size.
.TP
.B \-K \fItimeout_seconds
Ensure that traffic is transmitted at a certain interval in seconds. This is
useful for working around firewalls or routers that drop connections after
a certain period of inactivity. The trade-off is that a session may be
closed if there is a temporary lapse of network connectivity. A setting
if 0 disables keepalives. If no response is received for 3 consecutive keepalives the connection will be closed.
.TP
.B \-I \fIidle_timeout
Disconnect the session if no traffic is transmitted or received for \fIidle_timeout\fR seconds.
.TP
.B \-T \fImax_authentication_attempts
Set the number of authentication attempts allowed per connection. If unspecified the default is 10 (MAX_AUTH_TRIES)
.TP
.B \-c \fIforced_command
Disregard the command provided by the user and always run \fIforced_command\fR. This also
overrides any authorized_keys command= option.
.TP
.B \-V
Print the version

.SH FILES

.TP
Authorized Keys

~/.ssh/authorized_keys can be set up to allow remote login with a RSA,
ECDSA, Ed25519 or DSS
key. Each line is of the form
.TP
[restrictions] ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAIgAsp... [comment]

and can be extracted from a Dropbear private host key with "dropbearkey -y". This is the same format as used by OpenSSH, though the restrictions are a subset (keys with unknown restrictions are ignored).
Restrictions are comma separated, with double quotes around spaces in arguments.
Available restrictions are:

.TP
.B no-port-forwarding
Don't allow port forwarding for this connection

.TP
.B no-agent-forwarding
Don't allow agent forwarding for this connection

.TP
.B no-X11-forwarding
Don't allow X11 forwarding for this connection

.TP
.B no-pty
Disable PTY allocation. Note that a user can still obtain most of the
same functionality with other means even if no-pty is set.

.TP
.B command=\fR"\fIforced_command\fR"
Disregard the command provided by the user and always run \fIforced_command\fR.
The -c command line option overrides this.

The authorized_keys file and its containing ~/.ssh directory must only be
writable by the user, otherwise Dropbear will not allow a login using public
key authentication.

.TP
Host Key Files

Host key files are read at startup from a standard location, by default
/etc/dropbear/dropbear_dss_host_key, /etc/dropbear/dropbear_rsa_host_key,
/etc/dropbear/dropbear_ecdsa_host_key and /etc/dropbear/dropbear_ed25519_host_key

If the -r command line option is specified the default files are not loaded.
Host key files are of the form generated by dropbearkey. 
The -R option can be used to automatically generate keys
in the default location - keys will be generated after startup when the first
connection is established. This had the benefit that the system /dev/urandom
random number source has a better chance of being securely seeded.

.TP
Message Of The Day

By default the file /etc/motd will be printed for any login shell (unless 
disabled at compile-time). This can also be disabled per-user
by creating a file ~/.hushlogin .

.SH ENVIRONMENT VARIABLES
Dropbear sets the standard variables USER, LOGNAME, HOME, SHELL, PATH, and TERM.

The variables below are set for sessions as appropriate. 

.TP
.B SSH_TTY
This is set to the allocated TTY if a PTY was used.

.TP
.B SSH_CONNECTION
Contains "<remote_ip> <remote_port> <local_ip> <local_port>".

.TP
.B DISPLAY
Set X11 forwarding is used.

.TP
.B SSH_ORIGINAL_COMMAND
If a 'command=' authorized_keys option was used, the original command is specified
in this variable. If a shell was requested this is set to an empty value.

.TP
.B SSH_AUTH_SOCK
Set to a forwarded ssh-agent connection.

.SH NOTES
Dropbear only supports SSH protocol version 2.

.SH AUTHOR
Matt Johnston ([email protected]).
.br
Gerrit Pape ([email protected]) wrote this manual page.
.SH SEE ALSO
dropbearkey(1), dbclient(1), dropbearconvert(1)
.P
https://matt.ucc.asn.au/dropbear/dropbear.html