Original ipmsg protocol specification is written in Japanese.
This document was translated by Mr.Kanazawa.
This document is not verified yet. (too old...)

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       IP Messenger communication protocol (Draft-10)     1996/02/21
                                                 Modified 2014/11/08

                                                          H.Shirouzu
                                                    https://ipmsg.org
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About IP Messenger
	This is a Send/Receive message service using the TCP/UDP Port.

Characteristics
	IP Messenger can be installed in any OS if TCP/IP is used on your machine.
	Dynamic member recognition can be done within your network or specified network.
	You can exchange messages between all IPMsg members. 

Function description
	Use TCP/UDP port(default:2425). See the following descriptions
	(Message Send/Receive: UDP, File Send/Receive: TCP)

  1. Command 

     1) Command functions (Low 8 bits from command number 32 bits)

	IPMSG_NOOPERATION	No Operation
	IPMSG_BR_ENTRY		Entry to service (Start-up with a Broadcast command)
	IPMSG_BR_EXIT		Exit from service (End with a Broadcast command)
	IPMSG_ANSENTRY		Notify a new entry
	IPMSG_BR_ABSENCE	Change absence mode

	IPMSG_BR_ISGETLIST	Search valid sending host members
	IPMSG_OKGETLIST		Host list sending notice
	IPMSG_GETLIST		Host list sending request
	IPMSG_ANSLIST		Host list sending 

	IPMSG_SENDMSG		Message transmission
	IPMSG_RECVMSG		Message receiving check

	IPMSG_READMSG		Message open notice
	IPMSG_DELMSG		Message discarded notice
	IPMSG_ANSREADMSG	Message open confirmation notice(added from version-8)

	IPMSG_GETFILEDATA	File Transfer request by TCP
	IPMSG_RELEASEFILES	Discard attachment file
	IPMSG_GETDIRFILES	Attachment hierarchical file request

	IPMSG_GETINFO		Get IPMSG version info.
	IPMSG_SENDINFO		Send IPMSG version info.

	IPMSG_GETABSENCEINFO	Get absence sentence
	IPMSG_SENDABSENCEINFO	Send absence sentence

	IPMSG_GETPUBKEY		RSA Public Key Acquisition
	IPMSG_ANSPUBKEY		RSA Public Key Response

     2) Option flag (High 24 bits from command number 32 bits)

	IPMSG_ABSENCEOPT	Absence mode(Member recognition command)
	IPMSG_SERVEROPT		Server(Reserved)
	IPMSG_DIALUPOPT		Send individual member recognition command

	IPMSG_SENDCHECKOPT	Transmission check
	IPMSG_SECRETOPT		Sealed message
	IPMSG_READCHECKOPT	Sealed message check(added from ver8)
	IPMSG_PASSWORDOPT	Lock
	IPMSG_BROADCASTOPT	Broadcast message
	IPMSG_MULTICASTOPT	Multi-cast(Multiple casts selection)
	IPMSG_NEWMUTIOPT	New version multi-cast(reserved)
	IPMSG_NOLOGOPT		No log files
	IPMSG_NOADDLISTOPT	Notice to the members outside of BR_ENTRY
	IPMSG_AUTORETOPT	Automatic response(Ping-pong protection)

	IPMSG_FILEATTACHOPT	File attachment
	IPMSG_ENCRYPTOPT	Code
	IPMSG_ENCEXTMSGOPT	Encrypt file attach information

	IPMSG_CAPUTF8OPT	UTF-8 Capability
	IPMSG_UTF8OPT		Using UTF-8
	IPMSG_CLIPBOARDOPT	Clipboard image Capability

	IPMSG_RETRYOPT		Re-send flag(Use when acquiring HOSTLIST)

     3) Extended code flag (hex format combination)

	IPMSG_RSA_512
	IPMSG_RSA_1024
	IPMSG_RSA_2048
	IPMSG_RC2_40
	IPMSG_RC2_128
	IPMSG_RC2_256
	IPMSG_BLOWFISH_128
	IPMSG_AES_256
	IPMSG_PACKETNO_IV	Using PacketNo as AES Initial Vector
	IPMSG_ENCODE_BASE64
	IPMSG_SIGN_SHA1

     4) Extended files for attachment (fileattr low 8 bits)

	IPMSG_FILE_REGULAR
	IPMSG_FILE_DIR
	IPMSG_FILE_RETPARENT
	IPMSG_FILE_SYMLINK
	IPMSG_FILE_CDEV
	IPMSG_FILE_BDEV
	IPMSG_FILE_FIFO
	IPMSG_FILE_RESFORK

     5) Attachment file extended attribute(fileattr high 24 bits)

	IPMSG_FILE_RONLYOPT
	IPMSG_FILE_HIDDENOPT
	IPMSG_FILE_EXHIDDENOPT
	IPMSG_FILE_ARCHIVEOPT
	IPMSG_FILE_SYSTEMOPT

     6) Extended file attribute for attachment file

	IPMSG_FILE_UID
	IPMSG_FILE_USERNAME
	IPMSG_FILE_GID
	IPMSG_FILE_GROUPNAME
	IPMSG_FILE_PERM
	IPMSG_FILE_MAJORNO
	IPMSG_FILE_MINORNO
	IPMSG_FILE_CTIME
	IPMSG_FILE_MTIME
	IPMSG_FILE_ATIME
	IPMSG_FILE_CREATETIME

	IPMSG_FILE_CREATOR
	IPMSG_FILE_FILETYPE
	IPMSG_FILE_FINDERINFO

	IPMSG_FILE_ACL
	IPMSG_FILE_ALIASFNAME


  2.Command format(Use all character strings)

     1) Command(Format version-1)

	Ver(1) : PacketNo : SenderName : SenderHost : CommandNo : AdditionalSection

     2) An example for Message Send/Receive by using the current command format

	"1:100:shirouzu:jupiter:32:Hello"


  3.Command process overview

     1) Member recognition

	An IPMSG_BR_ENTRY command notifies a new entry to the current
	members at start-up.

	All members add the new member to their list after getting a notification message.
	An IPMSG_ANSENTRY command sends a message back to the new member.

	The new member gets the current member data by a
	IPMSG_ANSENTRY command. All members can communicate as long as an 
	IP packet exists.

	An IPMSG_BR_ABSENCE command broadcasts absence mode cancel or 
	nickname change to all members. However, an IPMSG_ANSENTRY command 
	does not send a message back, which is different from an IPMSG_BR_ENTRY 
	command.

	IPMSG_BR_ENTRY, IPMSG_ANSENTRY, and IPMSG_BR_ABSENCE commands 
	use an IPMSG_ABSENCEOPT flag for absence mode. Input a nickname to 
	additional command.
	Add an IPMSG_DIALUPOPT flag for dial-up users who can't be reached by 
	a broadcast command.  A member recognition command needs to be 
	sent individually to the members with this optional flag. 

	(Extended group)IPMSG_BR_ENTRY and IPMSG_BR_ABSENCE commands 
	sends a group name by adding the new group name after the current 
	command format character strings (Input '\0' between the current 
	command and extended name).

     2) Send/Receive Message
	Send Message uses an IPMSG_SENDMSG command that can input a message
	in the extended area. 
	Receive Message sends back an IPMSG_RECVMSG command only 
	if an IPMSG_SENDCHECKOPT flag is ON. Input the original packet number 
	to the extended area. 

	Broadcast Message Send uses an IPMSG_BOADCASTOPT command 
	and an IPMSG_SENDMSG flag should be ON. 
	Auto-Send packet(absence notice) needs to be added to IPMSG_AUTORETOPT
	for ping-pong protection. If either one or another packet is ON, then
	confirmation/auto-send packet is not sent back. 

	Send Message Sealing needs to be an IPMSG_SECRETOPT packet ON. 
	In this case, Receive Message sends an IPMSG_READMSG command.
	Input the original packet number to the extended area.

	(Additional IPMSG_NOADDLISTOPT)
	When receiving an IPMSG_SENDMSG packet from a host that is 
	not on your Send/Receive list, IPMsg will either confirm a host by 
	sending an IPMSG_BR_ENTRY command or add a host name to 
	the Send/Receive list. 
	However, single-shot Message Send/Receive action needs to be avoided. 
	Add an IPMSG_NOADDLISTOPT flag to an IPMSG_SENDMSG command.

	(Additional IPMSG_READCHECKOPT from version-8)
	When an IPMSG_READMSG command contains an IPMSG_READCHECKOPT flag, 
	IPMsg process is the same as IPMSG_SENDMSG with an 
	IPMSG_SENDCHECKOPT flag. 
	However, Send Message uses an IPMSG_ANSREADMSG command,  
	not IPMSG_RECVMSG.

     3) Message Send/Receive encrypted extension (Added in the version-9)

	Use the combination of Public-key(RSA) and common key(RC2/Blowfish).
	(Encrypted extension area is used in hex format.)

	(Public key acquisition)Send an IPMSG_GETPUBKEY command to Receive
	Message. Receive Message gets an IPMSG_ANSPUBKEY that 
	means receiving RSA public key from Send Message.

	IPMSG_GETPUBKEY/IPMSG_ANSPUBKEY both require the value which is
	encryption capability (Exp. IPMSG_RSA_1024) flag uses "OR" at first
	part of extension  

	In addition, In IPMSG_ANSPUBKEY, public key written as EE-NNNNNN
	E=Exponent, N=Modulus)devide by ':'. and Input the delimiter '-' 
	between E and N.

	This sequence can be skipped after the 2nd Send/Receive process by 
	memorizing public key and encrypted data. 
	
	(Encrypted message)After a sender creates a common key that is 
	supported both sender and receiver, a common key can encrypt a message. 
	In addition, a receiver's public key encrypts the common key.


	(Encrypted message transmission) IPMSG_ENCRYPTOPT is used in
	IPMSG_SENDMSG. At the first part of extension, input the value which
	is 'or' resoult from Convination of public key and common key type . 
	Then use common key which encrypt with public key devide by ':'.
	Then input message which is eccrypted by public key devide by ':'.
	If both supports IPMSG_SIGN_XXX, then add ':' and signeture. 

	Also, In the method of encode padding, PKCS#1ECB key is used for RSA, 
	PKCS#5 CBC common key is used for RC2/blowfish.

	Also, The Packet related to Entry manifestation the capability of 
	ecryption support using  IPMSG_ENCRYPTOPT

	(Message with Electric Signature) IPMSG_SIGN_SHA1 is used in
	IPMSG_SENDMSG. format is "encoded-message:RSA-sign(SHA-1(message))"

	(Username extension with pubkey-fingerprint)
	Support IPMSG_RSA_2048 and IPMSG_SIGN_SHA1, username format must use
	with pubkey-fingerprint. This extension prevent to impersonation and
	uniqueness.
	To generate finger print, it requires in the following 5 steps.
	   1. generate SHA-1(RSA-pubkey-Modulus) 160bit digeset.
	   2. separate 3parts of 64bit.
	       |        160bit             |
	       |   64bit  |   64bit  |32bit| + |32bit 0 value padding|
	       |   64bit  |   64bit  |   64bit  |
	   3. calcurate 64bit value of XOR 3 parts of 64bit. (finger print value)
	   4. encode 16 characters of hex.
	   5. add to username ... user-<64bit finger print as hex string>

	Recommend to check the signature from using this extension.

	(Inline image extension)
	inline image using file attach mechanism. but it requires to use
	IPMSG_FILE_CLIPBOARD option. it normaly PNG file.
	the insert position of a image, using IPMSG_FILE_CLIPBOARDPOS=pos
	that is extend-attr=val (see Extension with file attachment).
	If inserting multiple images, position value must add the number
	of previous images.
	 ex) message:  "abc[image1]cdef[image2]g..."
	     position:  012   3    4567   8    9...

	 To indicate a capability of inline image, use IPMSG_CLIPBOARDOPT in
	 IPMSG_BR_ENTRY/IPMSG_ANS_ENTRY/IPMSG_BR_ABSENCE command.


     4) Extension with file attachment(Available from version-9)

	An IPMSG_SENDMSG command with an IPMSG_FILEATTACHOPT flag for 
	File transfer (download permission)notification sends a message
	with attachment. 
	Input '\0' after the message and attachment file data.
	

	fileID:filename:size:mtime:fileattr[:extend-attr=val1
	[,val2...][:extend-attr2=...]]:\a:fileID...
	(size, mtime, and fileattr describe hex format. 
	 If a filename contains ':', please replace with "::".)

	When Receive Message downloads an attachment file, an IPMSG_GETFILEDATA 
	command requests a data transmission packet to the TCP port that is the same number  
	as the UDP sending port number. Input packetID:fileID:offset to the extended area. 
	(Use all hex format.)
	File Transfer side receives the request. After recognizing that it's a correct request, 
	then send the specified data (no format)

	When the data receiving side downloads a hierarchical attachment file, 
	use an IPMSG_GETDIRFILES command and input a packetID:fileID
	to the extended area and send a data transmission request packet. 
	(all hex format)

	Data sending side sends the following hierarchical data format.
	header-size:filename:file-size:fileattr[:extend-attr=val1
	[,val2...][:extend-attr2=...]]:contents-data
	Next headersize: Next filename...
	(All hex format except for filename and contetns-data)

	header-size is from the beginning of header-size to the delimiter ':' 
	that is before contents-data. extend-attr can be omitted and used multiple 
	extended attributes. Use '=' for data input. 

	When fileattr is IPMSG_FILE_DIR, IPMsg recognizes that it is automatically
	in the directory, the next file data is after the directory.

	When fileattr is IPMSG_FILE_RETPARENT, IMPsg recognizes that it returns 
	to the parent directory. In this case, File name is always "." and the attribute 
	value is the current directory data.

	Sending process starts from the attachment directly and returns the
	IPMSG_FILE_RETPARENT command to the attachment directory. 

	Add an IPMSG_FILEATTACHOPT flag for an Entry packet to support the 
	attachment file.

	 5) UTF-8 extension

	 To indicate a capability of UTF-8 message, use IPMSG_CAPUTF8OPT in
	 IPMSG_BR_ENTRY/IPMSG_ANS_ENTRY/IPMSG_BR_ABSENCE command.
	 Using UTF-8 message, use IPMSG_UTF8OPT in IPMSG_SENDMSG or etc.
	 But IPMSG_BR_ENTRY/IPMSG_BR_EXIT/IPMSG_BR_ABSENCE must not use
	 IPMSG_UTF8OPT, for backword compatibility (old clients).
	 So, add those entry after \0\n, (if belonging no group, using \0\0\n)
	   UN: username(utf-8)\n
	   HN: hostname(utf-8)\n
	   NN: nickname(utf-8)\n
	   GN: groupname(utf-8)\n

     6) Other commands

	When acquiring different versions, send an IPMSG_GETINFO command.
	Receiving side sends the version information character string to
	extended area.

	Send an IPMSG_GETABSENCEINFO command for acquiring an absence message.
	Receiving side sends an IPMSG_SENDABSENCEINFO back if the status is absence mode.
	If the status is not absence mode, a character string "Not absence mode" will be sent back.

     7) Confirmation/Retry

	If a confirmation packet for IPMSG_SENDMSG or IPMSG_RECVMSG is not delivered
	within a specified time, then it will be sent again. 
	A number of retry actions or interval period is depended on the current condition. 


  4. Other

     1) Linefeed

	Linefeed characters in Send Message is standardized with UNIX type ('0x0a').
	Please change if needed. 

     2) Delimiter ':'

	':' is used as a delimiter. You can't use this delimiter for user name 
	and host name. 
	If the use/host names contain a ':', please replace with another sign, 
	for an example ';'. 
	Although using this delimiter isn't problem as yet, I may create an 
	escape sequence. 
	

     3) Character codes

	If using IPMSG_UTF8OPT, using UTF-8, otherwise, using CP932.


  5. Contact
	https://ipmsg.org/ (Japanese site)
	https://ipmsg.org/index.html.en (English site)


Note
	See ipmsg.h for command codes.
	Please e-mail me your comments and suggestions.