One-time pad

One-time pad is a draft programming task. It is not yet considered ready to be promoted as a complete task, for reasons that should be found in its talk page.

Implement a One-time pad

Sub-Tasks

• generate the data for a One-time pad (user needs to specify a filename and length)

The important part is to get "true random" numbers, e.g. from /dev/random

• encryption / decryption ( basically the same operation, much like Rot-13 )

For this step, much of Vigenère cipher could be reused,
with the key to be read from the file containing the One-time pad.

• optional: management of One-time pads: list, mark as used, delete, etc.

Somehow, the users needs to keep track which pad to use for which partner.

To support the management of pad-files:

• such files have a file-extension ".otp"
• lines starting with "#" may contain arbitary meta-data (i.e. comments)
• lines starting with "-" count as "used"
• whitespace within the otp-data is ignored

For example, here is the data from Wikipedia:

# Example data - Wikipedia - 2014-11-13
-ZDXWWW EJKAWO FECIFE WSNZIP PXPKIY URMZHI JZTLBC YLGDYJ 
-HTSVTV RRYYEG EXNCGA GGQVRF FHZCIB EWLGGR BZXQDQ DGGIAK 
 YHJYEQ TDLCQT HZBSIZ IRZDYS RBYJFZ AIRCWI UCVXTW YKPQMK 
 CKHVEX VXYVCS WOGAAZ OUVVON GCNEVR LMBLYB SBDCDC PCGVJX 
 QXAUIP PXZQIJ JIUWYH COVWMJ UZOJHL DWHPER UBSRUJ HGAAPR 
 CRWVHI FRNTQW AJVWRT ACAKRD OZKIIB VIQGBK IJCWHF GTTSSE 
 EXFIPJ KICASQ IOUQTP ZSGXGH YTYCTI BAZSTN JKMFXI RERYWE 

Tcl

Part 1: random strings

Get true random numbers, and turn them into strings.

From Tcl'ers wiki Cryptographically secure random numbers using /dev/urandom

<lang Tcl>puts "# True random chars for one-time pad"

proc randInt { min max } {

   set randDev [open /dev/urandom rb]
   set random [read $randDev 8]
   binary scan $random H16 random
   set random [expr {([scan $random %x] % (($max-$min) + 1) + $min)}]
   close $randDev
   return $random

}

set alfa "ABCDEFGHIJKLMNOPQRSTUVWXYZ" set len 48 set rs "" for {set i 0} {$i < $len} {incr i} {

 if { [expr {$i % 6} ] == 0} { append rs " " }
 set r [randInt 1 26]
 set char [string index $alfa $r]
 append rs $char

} puts ":$rs." </lang>

Output:

# True random chars for one-time pad
: IDEVVW KCTMY KLKLID DSGKIV WHMOX LIEYWF MCIECW OUQVIV.

Todo: write strings to file ...

Part 2: Encrypt/Decrypt

See Tcl'ers wiki: vignere Vigenere ...

Part 3: Management

• list padfiles in directory
• list block between "comment"-lines in padfile

...