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# -*- tcl -*-
# # ## ### ##### ######## #############
# (C) 2009 Andreas Kupries
# @@ Meta Begin
# Package tcl::transform::otp 1
# Meta as::author {Andreas Kupries}
# Meta as::copyright 2009
# Meta as::license BSD
# Meta description Implementation of an onetimepad
# Meta description encryption transformation. Based on Tcl
# Meta description 8.6's transformation reflection support.
# Meta description The key bytes are read from two channels
# 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 Three arguments, the channel to extend,
# Meta description plus the channels to read the keys from.
# 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::otp {chan keychanw keychanr} {
::chan push $chan [otp::implementation new $keychanw $keychanr]
}
oo::class create ::tcl::transform::otp::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 Xor $data $keychanw]
}
method read {c data} {
return [my Xor $data $keychanr]
}
# # ## ### ##### ######## #############
constructor {keyw keyr} {
set keychanr $keyr
set keychanw $keyw
return
}
# # ## ### ##### ######## #############
variable keychanr keychanw
# # ## ### ##### ######## #############
# A very convoluted way to perform the XOR would be to use TIP
# #317's hex encoding to convert the bytes into strings, then zip
# key and data into an interleaved string (nibble wise), then
# perform the xor as a 'string map' of the whole thing, and at
# last 'binary decode hex' the string back into bytes. Even so
# most ops would run on the whole message at C level. Except for
# the interleave. :(
method Xor {data keychan} {
# xor is done byte-wise. to keep IO down we read the key bytes
# once, before the loop handling the bytes. Note that we are
# having binary data at this point, making it necessary to
# convert into numbers (scan), and back (binary format).
set keys [read $keychan [string length $data]]
set result {}
foreach d [split $data {}] k [split $keys {}] {
append result \
[binary format c \
[expr {
[scan $d %c] ^
[scan $k %c]
}]]
}
return $result
}
}
# # ## ### ##### ######## #############
package provide tcl::transform::otp 1
return
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