Direct Connect (file sharing)

Direct connect is a peer-to-peer file sharing protocol. Direct connect clients connect to a central hub and can download files directly from one another. Advanced Direct Connect can be considered a successor protocol.

Hubs feature a list of clients or users connected to them. Users can search for files and download them from other clients, as well as chat with other users.

History

NeoModus was started as a company funded by the adware "Direct Connect" by Jonathan Hess in November, 1999 while he was in high school.^[1] The first third-party client was called "DClite", which never fully supported the file sharing aspects of the protocol. Hess released a new version of Direct Connect, requiring a simple encryption key to initiate a connection, locking out third-party clients. The key was cracked, and the author of DClite released a new version of DClite compatible with the new software from NeoModus. Some time after, DClite was rewritten as Open Direct Connect with goals of having an MDI user interface and using plug-ins for file sharing protocols (similar to MLDonkey). Open Direct Connect also did not have complete support for the full file sharing aspects of the protocol, but a port to Java did. Some time later, other clients such as DCTC (Direct Connect Text Client) and DC++ became popular.

Protocol

The Direct connect protocol is a text-based computer protocol, in which commands and their information are sent in clear text, without encryption in original Neo-Modus software (of course encryption is available as protocol extension). As clients connect to a central source of distribution (the hub) of information, the hub is required to have a substantial amount of upload bandwidth available.^[2]

There is no official specification of the protocol. This means that every client and hub besides the original Neo-modus client and hub has been forced to reverse engineer the information. As such, any protocol specification this article may reference is likely either inaccurate and/or incomplete.^{[citation needed]}

The client-server (as well in client-client, where one acts as "server") aspect of the protocol stipulates that the server speak first when a connection has been made. For example, when a client connect to a hub's socket, the hub is first to talk to the client.

The protocol don't have specified default character encoding for clients or hubs. In original client and hub is use Ascii encoding of Operating system. This allow to move to UTF-8 encoding in newer software.

Port 411 is the default port for hubs, and 412 for client-to-client connections. If either of these ports is already in use, the next higher port is used. For example, if 411, 412 and 413 are in use, then port 414 will be used.

Hub addresses are in the following form: dchub://example.com[:411], where 411 is an optional port.

There is no global identification scheme; users are identified with their nickname on a hub-to-hub basis.

An incoming request for a client-client connection cannot be linked with an actual connection.^[3]

A search result cannot be linked with a particular search.^[4]

Supported by the protocol is the ability to kick or move (redirect) a user to another hub. There is no restriction on where a user might be redirected to. If a user is kicked, the hub isn't required to give the user a specific reason. However, if another client in power instructs the hub to kick, that client may send out a notification message before doing so. Redirecting a user must be accompanied by a reason. There is no HTTP referer equivalent.

Hubs may send out user commands to clients. These commands are only raw protocol commands, and are used mostly for making a particular task simpler. For example, the hub cannot send a user command that will trigger the default browser to visit a website. It can however add the command "+rules" (where '+' indicates to the hub that it's a command - this may vary) to display the hub's rules.

The peer-to-peer part of the protocol is based on a concept of "slots" (similar to number of open positions for a job). These slots denote the number of people that are allowed to download from a user at any one time. These slots are controlled by the client.

In client-to-client connections, the parties negotiate a random number to see who should be allowed to download first. The client with the highest number wins.

Downloads are transported using TCP. Active searches use UDP. The connection to the hub is with TCP.

There are two kinds of modes a user can be in, either "active" or "passive" mode. Clients using active mode can download from anyone else on the network. Clients using passive mode users can only download from active users. In NeoModus Direct Connect, passive mode users receive other passive mode users' search results, while the user will not be able to download anything. In DC++, users will not receive those search results. In NeoModus Direct Connect, all users will be sent at most five search results per query. If a user has searched, DC++ will respond with ten search results when the user is in active mode, or five, when the user is in passive mode. Passive clients will be sent search results through the hub, while active clients will receive the results directly.

Protocol delimiters are '$', '|' and ' ' (space). Protocol have for them (and few others) escape sequence and most software use them correctly in login (Lock to Key) sequence. For some reason that escape sequence was ignored by DC++ developers and they use HTML equivalent if these characters are to be viewed by the user.

Continued interest exists in features such as ratings and language packs. However, the authors of DC++ have been actively working on a complete replacement of the Direct connect protocol called Advanced Direct Connect.

One example of an added feature to the protocol, in comparison with the original protocol, is the broadcasting of Tiger-Tree Hashing of shared files (TTH). The advantages of this include verifying that a file is downloaded correctly, and the ability to find files independently of their names.

Hub software

Direct Connect hubs are central servers to which clients connect, thus the networks are not as decentralized as Gnutella or FastTrack. Hubs provide information about the clients, as well as file-searching and chat capabilities. File transfers are done directly between clients, in true peer-to-peer fashion.

Hubs often have special areas of interest. Many have requirements on the total size of the files that their members share (share size), and restrictions on the content and quality of shares. A hub can have any arbitrary rule. Hubs can allow users to register and provide user authentication. The authentication is also in clear text. The hub may choose certain individuals as operators (similar to IRC operators) to enforce said rules if the hub itself cannot.

While not directly supported by the protocol, hub linking software exists. The software allow multiple hubs to be connected, allowing users to share and / or chat with people on the other linked hubs. Direct connect hubs have difficulty scaling, due to the broadcast-centricity of the protocol.

General

NMDC hub	FOSS	Software license	Active	Latest version (release date)	GUI	CLI	Other	IPv6 support	Programming language	Based on
UFOHub	No	Proprietary Freeware	Yes	v7.9.11 (2011-09-15)	Yes	Unknown	Unknown	No	Unknown	UFOHub
PTDCH	Yes	GNU GPL	Yes		Yes	Unknown	Unknown	No	Visual Basic, Jscript, VBscript	DDCH
Dtella	Yes	GNU GPL	Yes	1.2.6 (2010-01-22)[5]	Unknown	Unknown	Unknown	No	Python
HeXHub	Yes	Open Software License	Yes	5.07 (2011-05-29)	Yes	Unknown	Unknown	No	Assembly
Open Direct Connect Hub	Yes	GNU GPL	No	0.8.2 (2010-04-09)	No	Unknown	Unknown	No	C, Perl
Flexhub	Yes	GNU AGPL	Yes		Unknown	Yes	Unknown	No	Lua
PtokaX	Yes	GNU GPL	Yes	0.4.2.0 (11 September 2011)[6]	Yes	Yes	Unknown	Yes	C++, Lua
RusHub	Yes	GNU GPL	Yes	2.3.7 (23 October 2011)[7]	No	Yes	Unknown	Yes	C++, Lua
VerliHub	Yes	GNU GPL	Yes	0.9.8e-r2 (2009-07-20)	No	Yes	Unknown	No	C++, Lua, Python
Eximius	No	Proprietary Freeware	Yes		Yes	Unknown	Unknown	No	C#, Lua
DB Hub	Yes	GNU GPL	No		Unknown	Unknown	Unknown	No	Unknown	OpenDCHub
openDCd	Yes	GNU GPL	No		Unknown	Unknown	Unknown	No	Unknown
DDCH DevDirect Connect Hub	Unknown	Unknown	No		Yes	No	No	No	Visual Basic, Jscript
py-dchub	Yes	MIT License	No	0.2.4 (2006-02-13)	Unknown	Unknown	Unknown	No	Python
Aquila	Yes	GNU GPL	No		No	Yes	No	No	C++, Lua
YnHub	No	Proprietary Freeware	No	1.036 (2008-03-23)	Yes	No	No	No	Delphi
X-Hub	Unknown	Unknown	No	0.3.1.0 ()	Unknown	Unknown	Unknown	No	C++
LamaHub	Yes	GNU GPL	No	0.0.6.3 (2010-04-25)	Unknown	Unknown	Unknown	No	C
DC Sharp Hub	Yes	GNU GPL	No	3.0.4 beta (2004-09-06)	Unknown	Unknown	Unknown	No	C#
NMDC hub	FOSS	Software license	Active	Latest version (release date)	GUI	CLI	Other	IPv6 support	Programming language	Based on

Operating system support

NMDC hub	Windows	Linux	Mac OS X	Other
UFOHub	Yes	No	No	No
Eximius	Yes	No	No	No
PTDCH	Yes	No	No	No
Aquila	Yes	Yes	No	No
Dtella	Yes	Yes	Yes	No
HeXHub	Yes	No	No	No
Open Direct Connect Hub	No	Yes	No	OpenWrt
Flexhub	Yes	Yes	No	No
openDCd	Yes	Yes	No	No
DDCH DevDirect Connect Hub	Yes	No	No	No
DBHub	No	Yes	No	No
PtokaX	Yes	Yes	No	FreeBSD, Nexenta
py-dchub	Yes	Yes	Yes	Any Python compatible platform
RusHub	Yes	Yes	No	FreeBSD
VerliHub	No	Yes	No	No
Yhub	Yes	No	No	No
Ynhub	Yes	No	No	No
xHub	Yes	Yes	No	No
LamaHub	Yes	Yes	Yes	OS/2, OpenBSD, NetBSD, PC-BSD, FreeBSD, ZeX/OS
DC Sharp Hub	Yes	No	No	No
NMDC hub	Windows	Linux	Mac OS X	Other

Client Software

While not mandated by the protocol, most clients send a "tag". This is part of the client's description and display information ranging from client name and version to number of total available slots to if the user is using a proxy server. It was originally added to DC++, due to its ability to be in multiple hubs with the same instance. The information is arbitrary. The original client's file list (a comprehensive list of the files a user shares) was compressed using Huffman's compression algorithm. Newer clients (among them DC++) serve an XML-based list, compressed with bzip2.

General

NMDC Client	FOSS	Software license	Active
MLDonkey	Yes	GNU GPL	Yes
Shareaza	Yes	GNU GPL	Yes
NeoModus Direct Connect	No	Proprietary Freeware	No
ShakesPeer	Yes	GNU GPL	No
Valknut	Yes	GNU GPL	No
DCTC	Yes	GNU GPL	No
DC#	Yes	GNU GPL	No
LDCC	Unknown	Unknown	No
DCDM++	Yes	GNU GPL	No
fulDC	Yes	GNU GPL	No
RevConnect	Yes	GNU GPL	No
CzDC	Yes	GNU GPL	Yes
EiskaltDC	Yes	GNU GPL	No
NMDC Client	FOSS	Software license	Active

Operating system support

NMDC Client	Windows	Linux	Mac OS X	Other
MLDonkey	Yes	Yes	Yes	No
Shareaza	Yes	No	No	No
NeoModus Direct Connect	Yes	Yes	No	No
ShakesPeer	No	No	Yes	No
Valknut	No	Yes	No	FreeBSD
DC#	Yes	No	No	No
LDCC	No	Yes	No	No
DCDM++	Yes	No	No	No
fulDC	Yes	No	No	No
RevConnect	Yes	No	No	No
CzDC	Yes	No	No	No
EiskaltDC	No	Yes	No	FreeBSD
NMDC Client	Windows	Linux	Mac OS X	Other

Interface and programming

NMDC Clients	GUI	CLI	Other	Programming language	Based on
MLDonkey	Yes	Yes	WebUI	Objective Caml, C, assembly
Shareaza	Yes	Unknown	Unknown	C++
NeoModus Direct Connect	Yes	No	No	Visual Basic, C++
ShakesPeer	Yes	No	No	C
Valknut	Yes	No	No	C++
DCTC	No	No	Yes	C++
DC#	Yes	No	No	C#
LDCC	No	No	Yes	C
DCDM++	Yes	No	No	C++	DC++
fulDC	Yes	No	No	C++	DC++
RevConnect	Yes	No	No	C++	DC++
CzDC	Yes	No	No	C++	DC++
EiskaltDC	Yes	No	No	C++	Valknut
NMDC Clients	GUI	CLI	Other	Programming language	Based on

Other Software

Hub linking software links hubs' main chat, so that users can see and respond to chat that is in a hub they're not directly connected to. Often used to draw in users to hubs, or make private or small hubs more widely known. Where as advertising a hub is "frowned upon" and is usually repercussion with floods or denial of service attacks, forming a more or less formal network by means of linking hub chat is a legitimate means for getting free publicity. Some Hub programs are able to support a more advanced form of linking which includes all the normal functions, chat, private messages, search and file transfers between users on different hubs can be supported through hub specific solutions or hub software neutral extensions using scripts/plug-ins.

General

Other software	Software type	FOSS	Software license	Active
jDCBot	General library	Yes	GNU GPL	Yes
Net::DirectConnect	General library	Yes	Unknown	Yes
FlowLib	General library	Yes	GNU GPL	Yes
DC-hublink	Link	Yes	GNU GPL	No
Hub-Link	Link	Yes	GNU GPL	No
MyIrcDcLinks	Link	Yes	GNU GPL	Yes
NetChatLink	Link	Yes	GNU GPL	Yes
Kitty	Bot	Yes	GNU GPL	No
Other software	Software type	FOSS	Software license	Active

Operating system support

Other software	Windows	Linux	Mac OS X	Other
jDCBot	Yes	Yes	Yes	Any Java compatible platform
Net::DirectConnect	Yes	Yes	Yes	Any Perl compatible platform
FlowLib	Yes	Yes	Yes	Any C# compatible platform
DC-hublink	Yes	No	No	No
Hub-Link	Yes	No	No	No
MyIrcDcLinks	Yes	No	No	No
NetChatLink	Yes	No	No	Runs under WINE
Kitty	Yes	No	No	No
Other software	Windows	Linux	Mac OS X	Other

Interface and programming

Other software	GUI	CLI	Other	Programming language	Based on
jDCbot	No	No	No	Java
Net::DirectConnect	No	No	No	Perl
FlowLib	No	No	No	C#
DC-hublink	Yes	No	No	Visual Basic
Hub-Link	Yes	No	No	Visual Basic
MyIrcDcLinks	Yes	No	No	Delphi
NetChatLink	Yes	No	No	Delphi
Kitty	Unknown	Unknown	Unknown	C#
Other software	GUI	CLI	Other	Programming language	Based on

Hublists

Name	NMDC	ADC	Active	Registration	CTM Detection	Active
dchublist.com/	Yes	Yes	Yes	Webbased	Yes	Yes
openhublist.org	Yes	Yes	Yes	Webbased	Yes	Yes
publichublist.nl	Yes	No	Yes	Regserver	Unknown	Yes
hublist.org.nz	Yes	Yes	Yes	Webbased	Unknown	Yes
dchublist.ru	Yes	No	Yes	Unknown	Unknown	Yes
qsdchublist.com	Yes	No	Yes	Webbased	Yes	Yes
Name	NMDC	ADC	Active	Registration	CTM Detection	Active

Direct Connect used for DDoS attacks

As the protocol allow hubs to redirect users to another hub, malicious hubs have redirected users to other places than real Direct Connect hubs, effectively causing a Distributed Denial of Service attack. As well, the hubs may alter the IP in client to client connections, pointing to a potential victim.^[8][9][10]

The CTM Exploit made its presence known during 2006-2007; it made the developers take security issues more seriously since the whole direct connect network suffered from DDoS attacks from this exploit. It's recommended for users to run later versions of the hub software due to this exploit. Many hublists have started to block insecure hubs.

As of February 2009^{[11][12] [13][14][15]} ,an extension for clients was proposed in order for the attacked party to find out the hub sending the connecting users.

References

1. ^ Annalee Newitz (July 2001). "Sharing the Data". Metro, Silicon Valley's Weekly Newspaper. Metro Publishing Inc. http://www.metroactive.com/papers/metro/07.12.01/work-0128.html. Retrieved 2006-10-16. 
2. ^ Fredrik Ullner (April 2007). "Command and bandwidth estimations in NMDC". DC++: Just These Guys, Ya Know?. http://dcpp.wordpress.com/2007/04/23/command-and-bandwidth-estimations-in-nmdc/. Retrieved 2007-07-27. 
3. ^ cologic (August 2007). "CTM tokens in ADC (or why the NMDC protocol is terrible, part 2)". DC++: Just These Guys, Ya Know?. http://dcpp.wordpress.com/2007/08/03/ctm-tokens-in-adc-or-why-the-nmdc-protocol-is-terrible-part-2/. Retrieved 2007-10-07. 
4. ^ Todd Pederzani (June 2006). "Filtering Redux". DC++: Just These Guys, Ya Know?. http://dcpp.wordpress.com/2006/06/04/filtering-redux/. Retrieved 2007-08-31. 
5. ^ http://dtella.org/changelog
6. ^ http://www.ptokax.org/news.html
7. ^ http://sourceforge.net/projects/rushub/files/RusHub/
8. ^ Paul Sop (May 2007). "Prolexic Distributed Denial of Service Attack Alert". Prolexic Technologies Inc.. Prolexic Technologies Inc.. Archived from the original on 2007-08-03. http://web.archive.org/web/20070803175513/http://www.prolexic.com/news/20070514-alert.php. Retrieved 2007-08-22. 
9. ^ Robert Lemos (May 2007). "Peer-to-peer networks co-opted for DOS attacks". SecurityFocus. http://www.securityfocus.com/news/11466. Retrieved 2007-08-22. 
10. ^ Fredrik Ullner (May 2007). "Denying distributed attacks". DC++: Just These Guys, Ya Know?. http://dcpp.wordpress.com/2007/05/22/denying-distributed-attacks/. Retrieved 2007-08-22. 
11. ^ Jan Vidar Krey (February 2009). "Referral extension". DC++ Launchpad Page. https://bugs.launchpad.net/dcplusplus/+bug/316096. Retrieved 2009-02-11. 
12. ^ Jan Vidar Krey (February 2009). "Referral extension on ADCPortal wiki". ADCPortal.com. http://www.adcportal.com/wiki/index.php/REF. Retrieved 2009-02-11. 
13. ^ Eugen Hristev (February 2009). "DC++ pointing out the corrupted". DC++: Just These Guys, Ya Know?. http://dcpp.wordpress.com/2009/02/11/dc-pointing-out-the-corrupted/. Retrieved 2009-02-11. 
14. ^ Toast (January 2009). "CTM Review and the errors of past". ADCPortal. http://www.adcportal.com/forums/viewtopic.php?f=10&t=431&start=0. Retrieved 2009-01-27. 
15. ^ Fredrik Ullner (July 2011). "Long lost response regarding DC being used as a DDoS tool". DC++: Just These Guys, Ya Know?. https://dcpp.wordpress.com/2011/07/20/long-lost-response-regarding-dc-being-used-as-a-ddos-tool/. Retrieved 2011-07-20. 

External links

• NMDC Protocol Wiki (Mirror)
• NMDC Protocol Document
• NMDC Protocol (No files to view/download?)
• NMDC Protocol Wiki (Doesn't work - expired domain as of Aug 2011. at least)(website transferred)