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# -*- tcl -*-
# # ## ### ##### ######## #############
# (C) 2009 Andreas Kupries
# @@ Meta Begin
# Package tcl::transform::rot 1
# Meta as::author {Andreas Kupries}
# Meta as::copyright 2009
# Meta as::license BSD
# Meta description Implementation of a rot
# Meta description encryption transformation. Based on Tcl
# Meta description 8.6's transformation reflection support.
# Meta description The key byte is
# Meta description configured at construction time. Exports
# Meta description a single command adding a new
# Meta description transformation of this type to a channel.
# Meta description Two arguments, the channel to extend,
# Meta description plus the key byte.
# Meta description No result.
# Meta platform tcl
# Meta require tcl::transform::core
# Meta require {Tcl 8.6}
# @@ Meta End
# # ## ### ##### ######## #############
package require Tcl 8.6
package require tcl::transform::core
# # ## ### ##### ######## #############
namespace eval ::tcl::transform {}
proc ::tcl::transform::rot {chan key} {
::chan push $chan [rot::implementation new $key]
}
oo::class create ::tcl::transform::rot::implementation {
superclass tcl::transform::core ;# -> initialize, finalize, destructor
# This transformation is intended for streaming operation. Seeking
# the channel while it is active may cause undesirable
# output. Proper behaviour may require the destruction of the
# transform before seeking.
method write {c data} {
return [my Rot $data $key]
}
method read {c data} {
return [my Rot $data $ikey]
}
# # ## ### ##### ######## #############
constructor {thekey} {
set key [expr {$thekey % 26}]
set ikey [expr {26 - $key}]
return
}
# # ## ### ##### ######## #############
variable key ikey
# # ## ### ##### ######## #############
method Rot {data key} {
# rot'ation is done byte-wise. Note that we are having binary
# data at this point, making it necessary to convert into
# numbers (scan), and back (binary format).
set result {}
foreach d [split $data {}] {
set dx [scan $d %c]
if {(65 <= $dx) && ($dx <= 90)} {
set n [binary format c \
[expr { (($dx - 65 + $key) % 26) + 65 }]]
} elseif {(97 <= $dx) && ($dx <= 122)} {
set n [binary format c \
[expr { (($dx - 97 + $key) % 26) + 97 }]]
} else {
set n $d
}
append result $n
}
return $result
}
}
# # ## ### ##### ######## #############
package provide tcl::transform::rot 1
return
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