<hardware, communications> (Modulator/demodulator) An
	electronic device for converting between serial data
	(typically {EIA-232}) from a computer and an audio signal
	suitable for transmission over a telephone line connected to
	another modem.  In one scheme the audio signal is composed of
	silence (no data) or one of two frequencies representing zero
	and one.

	Modems are distinguished primarily by the maximum data rate
	they support.  Data rates can range from 75 bits per second up
	to 56000 and beyond.  Data from the user (i.e. flowing from
	the local terminal or computer via the modem to the telephone
	line) is sometimes at a lower rate than the other direction,
	on the assumption that the user cannot type more than a few
	characters per second.

	Various data {compression} and error correction {algorithms}
	are required to support the highest speeds.  Other optional
	features are {auto-dial} (auto-call) and {auto-answer} which
	allow the computer to initiate and accept calls without human
	intervention.  Most modern modems support a number of
	different {protocols}, and two modems, when first connected,
	will automatically negotiate to find a common protocol (this
	process may be audible through the modem or computer's
	loudspeakers).  Some modem protocols allow the two modems to
	renegotiate ("retrain") if the initial choice of data rate is
	too high and gives too many transmission errors.

	A modem may either be internal (connected to the computer's
	{bus}) or external ("stand-alone", connected to one of the
	computer's {serial ports}).  The actual speed of transmission
	in characters per second depends not just the modem-to-modem
	data rate, but also on the speed with which the processor can
	transfer data to and from the modem, the kind of compression
	used and whether the data is compressed by the processor or
	the modem, the amount of noise on the telephone line (which
	causes retransmissions), the serial character format
	(typically {8N1}: one {start bit}, eight data bits, no
	{parity}, one {stop bit}).

	See also {acoustic coupler}, {adaptive answering}, {baud
	barf}, {Bulletin Board System}, {Caller ID}, {SoftModem},
	{U.S. Robotics}, {UUCP}, {whalesong}.

	{Usenet} newsgroup: {news:comp.dcom.modems}.

	(2002-05-04)

[IRC] To cause somebody to be removed from a {IRC} channel, an
	option only available to {CHOPs}.  This is an extreme measure,
	often used to combat extreme {flamage} or {flood}ing, but
	sometimes used at the chop's whim.  Compare {gun}.

	[{Jargon File}]

[{Usenet}] 1. To duplicate a portion (or whole) of another's
	message (typically with attribution to the source) in a reply
	or followup, for clarifying the context of one's response.
	See the discussion of inclusion styles under "Hacker Writing
	Style".

	2. [{C}] "#include <disclaimer.h>" has appeared in {sig
	blocks} to refer to a notional "standard {disclaimer} file".

	[{Jargon File}]

<networking> (Note: not capitalised) Any set of networks
	interconnected with {routers}.  The {Internet} is the biggest
	example of an internet.

	(1996-09-17)

A language proposed by Cii {Honeywell-Bull} to meet the DoD
	{Ironman} requirements which led to {Ada}.  This language won
	in 1979.

	["On the GREEN Language Submitted to the DoD", E.W. Dijkstra,
	SIGPLAN Notices 13(10):16-21 (Oct 1978)].

	(1994-12-02)

In {object-oriented programming} sending a message to an
	{object} (to invoke a {method}) is equivalent to calling a
	{procedure} in traditional programming languages, except that
	the actual code executed may only be selected at run time
	depending on the {class} of the object.  Thus, in response to
	the message "drawSelf", the method code invoked would be
	different if the target object were a circle or a square.

	(1995-02-16)

<tool, cryptography> (PGP) A high security {RSA} {public-key
	encryption} application for {MS-DOS}, {Unix}, {VAX/VMS}, and
	other computers.  It was written by {Philip R. Zimmermann}
	<pkz@acm.org> of Phil's Pretty Good(tm) Software and later
	augmented by a cast of thousands, especially including Hal
	Finney, Branko Lankester, and Peter Gutmann.

	PGP was distributed as "{guerrilla freeware}".  The authors
	don't mind if it is distributed widely, just don't ask Philip
	Zimmermann to send you a copy.  PGP uses a {public-key
	encryption} {algorithm} claimed by US patent #4,405,829.  The
	exclusive rights to this patent are held by a California
	company called {Public Key Partners}, and you may be
	infringing this patent if you use PGP in the USA.  This is
	explained in the PGP User's Guide, Volume II.

	PGP allows people to exchange files or messages with {privacy}
	and {authentication}.  Privacy and authentication are provided
	without managing the keys associated with conventional
	cryptographic software.  No secure channels are needed to
	exchange keys between users, which makes PGP much easier to
	use.  This is because PGP is based on {public-key
	cryptography}.

	PGP encrypts data using the {International Data Encryption
	Algorithm} with a random {session key}, and uses the {RSA}
	algorithm to encrypt the session key.

	In December 1994 Philip Zimmermann faced prosecution for
	"exporting" PGP out of the United States but in January 1996
	the US Goverment dropped the case.  A US law prohibits the
	export of {encryption} software out of the country.
	Zimmermann did not do this, but the US government hoped to
	establish the proposition that posting an encryption program
	on a {BBS} or on the {Internet} constitutes exporting it - in
	effect, stretching export control into domestic censorship.
	If the government had won it would have had a chilling effect
	on the free flow of information on the global network, as well
	as on everyone's privacy from government snooping.

	{FAQ (ftp://ftp.netcom.com/pub/mp/mpj/getpgp.asc)}.  {UK FTP
	(ftp://src.doc.ic.ac.uk/packages/pgp/)}.  {USA FTP
	(http://web.mit.edu/network/pgp-form.html)}.
	{(http://www.pegasus.esprit.ec.org/people/arne/pgp.html)}.

	{Justice Dept. announcement
	(http://www.eff.org/pub/Alerts/usatty_pgp_011196.announce)}.

	["Protect Your Privacy: A Guide for PGP Users", William
	Stallings, Prentice-Hall, ISBN 0-13-185596-4].

	(1996-04-07)

1. <database> A value used to identify a {record} in a
	database, derived by applying some fixed function to the
	record.  The key is often simply one of the {fields} (a
	{column} if the database is considered as a table with records
	being rows, see "{key field}").  Alternatively the key may be
	obtained by applying some function, e.g. a {hash function}, to
	one or more of the fields.  The set of keys for all records
	forms an {index}.  Multiple indexes may be built for one
	database depending on how it is to be searched.

	2. <cryptography> A value which must be fed into the
	{algorithm} used to decode an encrypted message in order to
	reproduce the original {plain text}.  Some encryption schemes
	use the same (secret) key to encrypt and decrypt a message,
	but {public key encryption} uses a "private" (secret) key and
	a "public" key which is known by all parties.

	3. <hardware> An electromechanical {keyboard} button.

	(2003-07-04)