md2(n) md2(n) 







md2 - Message digest "md2"








package require Tcl ?8.2?


package require Trf ?2.1.4?


md2 ?options...? ?data?












The command md2 is one of several message digests provided
    by the package trf. See trf-intro for an overview of the whole
    package.



  

  
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.







  

  
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:

  







  

  
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".

  

  

  
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.

  

  
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.









  

  
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.

  

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

  

  
Like option -write-type, but for option
    -read-destination.

  

  
This option can be used for digests in mode write or
      transparent. The value data is either the name of a global
      (or namespaced) variable or the handle of a writable channel, dependent on
      the value of option -write-type. The message digest computed 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 \0's.

  

  

  
This option can be used for digests in mode write or
      transparent. The value data is either the name of a global
      (or namespaced) 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 \0'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.





  

  
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.

  

  

  
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.

  

  

  
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
        command itself.

  












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 command 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
    commandline 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 \0 characters embedded into either input or output.








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








authentication, hash, hashing, mac, md2, message digest








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








  

    2.1.4
    Trf transformer commands