md5_otp(n)																md5_otp(n)

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NAME

       md5_otp - Message digest "md5_otp"

SYNOPSIS

       package require Tcl  ?8.2?

       package require Trf  ?2.1.4?

       md5_otp ?options...? ?data?

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DESCRIPTION

       The command md5_otp is one of several message digests provided by the package trf. See trf-intro for an overview of the whole package.

       md5_otp ?options...? ?data?
	      The  options  listed  below  are understood by the digest if and only if the digest is attached to a channel.  See section IMMEDIATE
	      versus ATTACHED for an explanation of the term attached.

	      -mode absorb|write|transparent
		     This option has to be present. The specified argument determines the behaviour of the digest in attached mode.

		     Beyond the argument values listed above all unique abbreviations are recognized too. Their meaning is explained below:

		     absorb All data written to the channel is used to calculate the value of the message digest and then passed unchanged to  the
			    next  level in the stack of transformations for the channel the digest is attached to.  When the channel is closed the
			    completed digest is written out too, essentially attaching the vlaue of the diggest  after	the  information  actually
			    written to the channel.

			    When reading from the channel a value for the digest is computed too, and after closing of the channel compared to the
			    digest which was attached, i.e. came behind the actual data.  The option -matchflag has to be specified  so  that  the
			    digest knows where to store the result of said comparison. This result is a string and either "ok", or "failed".

		     write  All  data  read  from or written to the channel the digest is attached to is ignored and thrown away. Only a value for
			    the digest of the data is computed.  When the channel is closed the computed values are stored as ordered through  the
			    options -write-destination, -write-type, -read-destination, and -read-type.

		     transparent
			    This  mode	is  a  mixture of both absorb and write modes. As for absorb all data, read or written, passes through the
			    digest unchanged. The generated values for the digest however are handled in the same way as for write.

	      -matchflag varname
		     This option can be used if and only if the option "-mode absorb" is present. In that situation the argument is the name of  a
		     global or namespaced variable. The digest will write the result of comparing two digest values into this variable. The option
		     will be ignored if the channel is write-only, because in that case there will be no comparison of digest values.

	      -write-type variable|channel
		     This option can be used for digests in mode write or transparent. Beyond the values listed above all their  unique  abbrevia-
		     tions  are  also allowed as argument values.  The option determines the type of the argument to option -write-destination. It
		     defaults to variable.

	      -read-type variable|channel
		     Like option -write-type, but for option -read-destination.

	      -write-destination data
		     This option can be used for digests in mode write or transparent.	The value data is either the name of a global  (or  names-
		     paced)  variable  or  the handle of a writable channel, dependent on the value of option -write-type. The message digest com-
		     puted for data written to the attached channel is written into it after the attached  channel  was  closed.   The	option	is
		     ignored if the channel is read-only.

		     Note that using a variable may yield incorrect results under tcl 7.6, due to embedded 's.

	      -read-destination data
		     This  option  can be used for digests in mode write or transparent.  The value data is either the name of a global (or names-
		     paced) variable or the handle of a writable channel, dependent on the value of option -read-type. The message digest computed
		     for  data	read from the attached channel is written into it after the attached channel was closed.  The option is ignored if
		     the channel is write-only.

		     Note that using a variable may yield incorrect results under tcl 7.6, due to embedded 's.

       The options listed below are always understood by the digest, attached versus immediate does  not  matter.  See	section  IMMEDIATE  versus
       ATTACHED for explanations of these two terms.

	      -attach channel
		     The presence/absence of this option determines the main operation mode of the transformation.

		     If present the transformation will be stacked onto the channel whose handle was given to the option and run in attached mode.
		     More about this in section IMMEDIATE versus ATTACHED.

		     If the option is absent the transformation is used in immediate mode and the options listed below are recognized. More  about
		     this in section IMMEDIATE versus ATTACHED.

	      -in channel
		     This  options is legal if and only if the transformation is used in immediate mode. It provides the handle of the channel the
		     data to transform has to be read from.

		     If the transformation is in immediate mode and this option is absent the data to transform is expected as the  last  argument
		     to the transformation.

	      -out channel
		     This  options is legal if and only if the transformation is used in immediate mode. It provides the handle of the channel the
		     generated transformation result is written to.

		     If the transformation is in immediate mode and this option is absent the generated data is returned as the result of the com-
		     mand itself.

IMMEDIATE VERSUS ATTACHED

       The transformation distinguishes between two main ways of using it. These are the immediate and attached operation modes.

       For the attached mode the option -attach is used to associate the transformation with an existing channel. During the execution of the com-
       mand no transformation is performed, instead the channel is changed in such a way, that from then on all data written to or  read  from	it
       passes through the transformation and is modified by it according to the definition above.  This attachment can be revoked by executing the
       command unstack for the chosen channel. This is the only way to do this at the Tcl level.

       In the second mode, which can be detected by the absence of option -attach, the transformation immediately takes data from either its  com-
       mandline  or  a	channel,  transforms it, and returns the result either as result of the command, or writes it into a channel.  The mode is
       named after the immediate nature of its execution.

       Where the data is taken from, and delivered to, is governed by the presence and absence of the options -in and -out.  It  should  be  noted
       that this ability to immediately read from and/or write to a channel is an historic artifact which was introduced at the beginning of Trf's
       life when Tcl version 7.6 was current as this and earlier versions have trouble to deal with  characters embedded into  either  input	or
       output.

SEE ALSO

       adler, crc, crc-zlib, haval, md2, md5, md5_otp, ripemd-128, ripemd-160, sha, sha1, sha1_otp, trf-intro

KEYWORDS

       authentication, hash, hashing, mac, md5_otp, message digest

COPYRIGHT

       Copyright (c) 1996-2003, Andreas Kupries <andreas_kupries@users.sourceforge.net>

Trf transformer commands					       2.1.4								md5_otp(n)