NAME¶
sha1_otp - Message digest "sha1_otp"
SYNOPSIS¶
package require
Tcl ?8.2?
package require
Trf ?2.1.3?
sha1_otp ?
options...? ?
data?
DESCRIPTION¶
The command
sha1_otp is one of several message digests provided by the
package
trf. See
trf-intro for an overview of the whole package.
- sha1_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
abbreviations 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 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.
- -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 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.
- -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 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.
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, message digest, sha1_otp
COPYRIGHT¶
Copyright (c) 1996-2003, Andreas Kupries <andreas_kupries@users.sourceforge.net>
