SMALL dropbear server binary

Thu May 14 20:52:59 WST 2009

The difference will be uClibc, yes. Have a look at their
buildroot system, that should be able to easily build a
binary. Alternatively, don't build it statically and it will
be even smaller.

I haven't checked that 110kB is still attainable with the
current codebase, though it should still be in that general
ballpark.

Matt

On Thu, May 14, 2009 at 05:49:59PM +0530, Sourav Chakraborty wrote:
> Hello List,
> We are basically requiring a small footprint dropbear server binary for x86 linux and have hence followed the steps--
> 1. have downloaded dropbear-0.52 source code in tar.gz format.
> 2. ./configure --disable-zlib --disable-syslog
> 3. modified the Makefile to append--
> -ffunction-sections -fdata-sections -DLTC_NO_BSWAP with CFLAGS and
> -Wl,--gc-sections with LDFLAGS4.modified options.h file --(attached)5. make STATIC=1 MULTI=1 PROGRAMS=dropbear
> 6. strip dropbear
> 
> We have done the above on x86 machine having FC3 linux with gcc 3.4.2 20041017.
> 
> The dropbear binary generated after the "strip" is of size 549120 bytes i.e ~549kB.But from the msg archive I could see that --
> "A small memory footprint suitable for
> > memory-constrained environments - Dropbear can compile
> > to a 110kB statically linked binary with uClibc (and
> > only minimal options selected)."
> Of course I am not using uClibc,but is that the reason for such a difference in the footprint?What else can I do to decreasethe footprint to a size of 110kB as mentioned?Please reply asap as this is kind of urgent :-)Thanks and RegardsSourav

> /* Dropbear SSH
>  * Copyright (c) 2002,2003 Matt Johnston
>  * All rights reserved. See LICENSE for the license. */
> 
> #ifndef _OPTIONS_H_
> #define _OPTIONS_H_
> 
> /******************************************************************
>  * Define compile-time options below - the "#ifndef DROPBEAR_XXX .... #endif"
>  * parts are to allow for commandline -DDROPBEAR_XXX options etc.
>  ******************************************************************/
> 
> #ifndef DROPBEAR_DEFPORT
> #define DROPBEAR_DEFPORT "22"
> #endif
> 
> #ifndef DROPBEAR_DEFADDRESS
> /* Listen on all interfaces */
> #define DROPBEAR_DEFADDRESS ""
> #endif
> 
> /* Default hostkey paths - these can be specified on the command line */
> #ifndef DSS_PRIV_FILENAME
> #define DSS_PRIV_FILENAME "/etc/dropbear/dropbear_dss_host_key"
> #endif
> #ifndef RSA_PRIV_FILENAME
> #define RSA_PRIV_FILENAME "/etc/dropbear/dropbear_rsa_host_key"
> #endif
> 
> /* Set NON_INETD_MODE if you require daemon functionality (ie Dropbear listens
>  * on chosen ports and keeps accepting connections. This is the default.
>  *
>  * Set INETD_MODE if you want to be able to run Dropbear with inetd (or
>  * similar), where it will use stdin/stdout for connections, and each process
>  * lasts for a single connection. Dropbear should be invoked with the -i flag
>  * for inetd, and can only accept IPv4 connections.
>  *
>  * Both of these flags can be defined at once, don't compile without at least
>  * one of them. */
> #define NON_INETD_MODE
> #define INETD_MODE
> 
> /* Setting this disables the fast exptmod bignum code. It saves ~5kB, but is
>  * perhaps 20% slower for pubkey operations (it is probably worth experimenting
>  * if you want to use this) */
> /*#define NO_FAST_EXPTMOD*/
> //sourav
> #define NO_FAST_EXPTMOD
> 
> /* Set this if you want to use the DROPBEAR_SMALL_CODE option. This can save
> several kB in binary size, however will make the symmetrical ciphers (AES, DES
> etc) slower (perhaps by 50%). Recommended for most small systems. */
> #define DROPBEAR_SMALL_CODE
> 
> /* Enable X11 Forwarding - server only */
> //sourav
> /*#define ENABLE_X11FWD*/
> 
> /* Enable TCP Fowarding */
> /* 'Local' is "-L" style (client listening port forwarded via server)
>  * 'Remote' is "-R" style (server listening port forwarded via client) */
> //sourav
> /*#define ENABLE_CLI_LOCALTCPFWD
> #define ENABLE_CLI_REMOTETCPFWD
> 
> #define ENABLE_SVR_LOCALTCPFWD
> #define ENABLE_SVR_REMOTETCPFWD*/
> 
> /* Enable Authentication Agent Forwarding - server only for now */
> //sourav
> /*#define ENABLE_AGENTFWD*/
> 
> 
> /* Note: Both ENABLE_CLI_PROXYCMD and ENABLE_CLI_NETCAT must be set to
>  * allow multihop dbclient connections */
> 
> /* Allow using -J <proxycommand> to run the connection through a 
>    pipe to a program, rather the normal TCP connection */
> //sourav
> /*#define ENABLE_CLI_PROXYCMD*/
> 
> /* Enable "Netcat mode" option. This will forward standard input/output
>  * to a remote TCP-forwarded connection */
> //sourav
> /*#define ENABLE_CLI_NETCAT*/
> 
> /* Encryption - at least one required.
>  * Protocol RFC requires 3DES and recommends AES128 for interoperability.
>  * Including multiple keysize variants the same cipher 
>  * (eg AES256 as well as AES128) will result in a minimal size increase.*/
> //sourav
> /*#define DROPBEAR_AES128*/
> #define DROPBEAR_3DES
> /*#define DROPBEAR_AES256*/
> /*#define DROPBEAR_BLOWFISH*/
> /*#define DROPBEAR_TWOFISH256*/
> /*#define DROPBEAR_TWOFISH128*/
> 
> /* Enable "Counter Mode" for ciphers. This is more secure than normal
>  * CBC mode against certain attacks. This adds around 1kB to binary 
>  * size and is recommended for most cases */
> #define DROPBEAR_ENABLE_CTR_MODE
> 
> /* Message Integrity - at least one required.
>  * Protocol RFC requires sha1 and recommends sha1-96.
>  * sha1-96 may be of use for slow links, as it has a smaller overhead.
>  *
>  * Note: there's no point disabling sha1 to save space, since it's used
>  * for the random number generator and public-key cryptography anyway.
>  * Disabling it here will just stop it from being used as the integrity portion
>  * of the ssh protocol.
>  *
>  * These hashes are also used for public key fingerprints in logs.
>  * If you disable MD5, Dropbear will fall back to SHA1 fingerprints,
>  * which are not the standard form. */
> #define DROPBEAR_SHA1_HMAC
> /*#define DROPBEAR_SHA1_96_HMAC*/
> //sourav
> /*#define DROPBEAR_MD5_HMAC*/
> 
> /* Hostkey/public key algorithms - at least one required, these are used
>  * for hostkey as well as for verifying signatures with pubkey auth.
>  * Removing either of these won't save very much space.
>  * SSH2 RFC Draft requires dss, recommends rsa */
> #define DROPBEAR_RSA
> //sourav
> /*#define DROPBEAR_DSS*/
> 
> /* RSA can be vulnerable to timing attacks which use the time required for
>  * signing to guess the private key. Blinding avoids this attack, though makes
>  * signing operations slightly slower. */
> #define RSA_BLINDING
> 
> /* Define DSS_PROTOK to use PuTTY's method of generating the value k for dss,
>  * rather than just from the random byte source. Undefining this will save you
>  * ~4k in binary size with static uclibc, but your DSS hostkey could be exposed
>  * if the random number source isn't good. In general this isn't required */
> /* #define DSS_PROTOK */
> 
> /* Whether to do reverse DNS lookups. */
> //sourav
> /*#define DO_HOST_LOOKUP*/
> 
> /* Whether to print the message of the day (MOTD). This doesn't add much code
>  * size */
> //sourav
> /*#define DO_MOTD*/
> 
> /* The MOTD file path */
> #ifndef MOTD_FILENAME
> #define MOTD_FILENAME "/etc/motd"
> #endif
> 
> /* Authentication Types - at least one required.
>    RFC Draft requires pubkey auth, and recommends password */
> 
> /* Note: PAM auth is quite simple, and only works for PAM modules which just do
>  * a simple "Login: " "Password: " (you can edit the strings in svr-authpam.c).
>  * It's useful for systems like OS X where standard password crypts don't work,
>  * but there's an interface via a PAM module - don't bother using it otherwise.
>  * You can't enable both PASSWORD and PAM. */
> 
> #define ENABLE_SVR_PASSWORD_AUTH
> /* PAM requires ./configure --enable-pam */
> /*#define ENABLE_SVR_PAM_AUTH*/
> //sourav
> /*#define ENABLE_SVR_PUBKEY_AUTH*/
> 
> /* Wether to ake public key options in authorized_keys file into account */
> #ifdef ENABLE_SVR_PUBKEY_AUTH
> #define ENABLE_SVR_PUBKEY_OPTIONS
> #endif
> 
> #define ENABLE_CLI_PASSWORD_AUTH
> #define ENABLE_CLI_PUBKEY_AUTH
> #define ENABLE_CLI_INTERACT_AUTH
> 
> /* This variable can be used to set a password for client
>  * authentication on the commandline. Beware of platforms
>  * that don't protect environment variables of processes etc. Also
>  * note that it will be provided for all "hidden" client-interactive
>  * style prompts - if you want something more sophisticated, use 
>  * SSH_ASKPASS instead. Comment out this var to remove this functionality.*/
> #define DROPBEAR_PASSWORD_ENV "DROPBEAR_PASSWORD"
> 
> /* Define this (as well as ENABLE_CLI_PASSWORD_AUTH) to allow the use of
>  * a helper program for the ssh client. The helper program should be
>  * specified in the SSH_ASKPASS environment variable, and dbclient
>  * should be run with DISPLAY set and no tty. The program should
>  * return the password on standard output */
> /*#define ENABLE_CLI_ASKPASS_HELPER*/
> 
> /* Random device to use - define either DROPBEAR_RANDOM_DEV or
>  * DROPBEAR_PRNGD_SOCKET.
>  * DROPBEAR_RANDOM_DEV is recommended on hosts with a good /dev/(u)random,
>  * otherwise use run prngd (or egd if you want), specifying the socket. 
>  * The device will be queried for a few dozen bytes of seed a couple of times
>  * per session (or more for very long-lived sessions). */
> 
> /* We'll use /dev/urandom by default, since /dev/random is too much hassle.
>  * If system developers aren't keeping seeds between boots nor getting
>  * any entropy from somewhere it's their own fault. */
> #define DROPBEAR_RANDOM_DEV "/dev/urandom"
> 
> /* prngd must be manually set up to produce output */
> /*#define DROPBEAR_PRNGD_SOCKET "/var/run/dropbear-rng"*/
> 
> /* Specify the number of clients we will allow to be connected but
>  * not yet authenticated. After this limit, connections are rejected */
> /* The first setting is per-IP, to avoid denial of service */
> #ifndef MAX_UNAUTH_PER_IP
> #define MAX_UNAUTH_PER_IP 5
> #endif
> 
> /* And then a global limit to avoid chewing memory if connections 
>  * come from many IPs */
> #ifndef MAX_UNAUTH_CLIENTS
> #define MAX_UNAUTH_CLIENTS 30
> #endif
> 
> /* Maximum number of failed authentication tries (server option) */
> #ifndef MAX_AUTH_TRIES
> #define MAX_AUTH_TRIES 10
> #endif
> 
> /* The default file to store the daemon's process ID, for shutdown
>    scripts etc. This can be overridden with the -P flag */
> #ifndef DROPBEAR_PIDFILE
> #define DROPBEAR_PIDFILE "/var/run/dropbear.pid"
> #endif
> 
> /* The command to invoke for xauth when using X11 forwarding.
>  * "-q" for quiet */
> #ifndef XAUTH_COMMAND
> #define XAUTH_COMMAND "/usr/X11R6/bin/xauth -q"
> #endif
> 
> /* if you want to enable running an sftp server (such as the one included with
>  * OpenSSH), set the path below. If the path isn't defined, sftp will not
>  * be enabled */
> #ifndef SFTPSERVER_PATH
> #define SFTPSERVER_PATH "/usr/libexec/sftp-server"
> #endif
> 
> /* This is used by the scp binary when used as a client binary. If you're
>  * not using the Dropbear client, you'll need to change it */
> #define _PATH_SSH_PROGRAM "/usr/bin/dbclient"
> 
> /* Whether to log commands executed by a client. This only logs the 
>  * (single) command sent to the server, not what a user did in a 
>  * shell/sftp session etc. */
> /* #define LOG_COMMANDS */
> 
> /* Window size limits. These tend to be a trade-off between memory
>    usage and network performance: */
> /* Size of the network receive window. This amount of memory is allocated
>    as a per-channel receive buffer. Increasing this value can make a
>    significant difference to network performance. 24kB was empirically
>    chosen for a 100mbit ethernet network. The value can be altered at
>    runtime with the -W argument. */
> #define DEFAULT_RECV_WINDOW 24576
> /* Maximum size of a received SSH data packet - this _MUST_ be >= 32768
>    in order to interoperate with other implementations */
> #define RECV_MAX_PAYLOAD_LEN 32768
> /* Maximum size of a transmitted data packet - this can be any value,
>    though increasing it may not make a significant difference. */
> #define TRANS_MAX_PAYLOAD_LEN 16384
> 
> /* Ensure that data is transmitted every KEEPALIVE seconds. This can
> be overridden at runtime with -K. 0 disables keepalives */
> #define DEFAULT_KEEPALIVE 0
> 
> /* Ensure that data is received within IDLE_TIMEOUT seconds. This can
> be overridden at runtime with -I. 0 disables idle timeouts */
> #define DEFAULT_IDLE_TIMEOUT 0
> 
> /* The default path. This will often get replaced by the shell */
> #define DEFAULT_PATH "/usr/bin:/bin"
> 
> /* Some other defines (that mostly should be left alone) are defined
>  * in sysoptions.h */
> #include "sysoptions.h"
> 
> #endif /* _OPTIONS_H_ */