Richard Suchenwirth 2013-07-25 - Here is a little experiment with using a substring of the (first 1000) digits of pi as a very simple one-time pad for rot-n encryption.
set pi [join {
141592653589793238462643383279502884197169399375105
82097494459230781640628620899862803482534211706798
21480865132823066470938446095505822317253594081284
81117450284102701938521105559644622948954930381964
42881097566593344612847564823378678316527120190914
56485669234603486104543266482133936072602491412737
24587006606315588174881520920962829254091715364367
89259036001133053054882046652138414695194151160943
30572703657595919530921861173819326117931051185480
74462379962749567351885752724891227938183011949129
83367336244065664308602139494639522473719070217986
09437027705392171762931767523846748184676694051320
00568127145263560827785771342757789609173637178721
46844090122495343014654958537105079227968925892354
20199561121290219608640344181598136297747713099605
18707211349999998372978049951059731732816096318595
02445945534690830264252230825334468503526193118817
10100031378387528865875332083814206171776691473035
98253490428755468731159562863882353787593751957781
8577805321712268066130019278766111959092164201989
} ""]
proc picryp {str pad {sgn ""}} {
set res ""
foreach char [split $str ""] digit [split $pad ""] {
append res [rot $char $sgn$digit]
}
return $res
}
proc rot {char amount} {
set alphabet "ABCDEFGHIJKLMNOPQRSTUVWXYZ abcdefghijklmnopqrstuvwxyz"
set pos [string first $char $alphabet]
return [expr {$pos == -1 ? $char : [string index $alphabet [expr {($pos + $amount)%[string length $alphabet]}]]}]
}Testing:
% set cr [picryp "Hello Tcl world" [string range $pi 42 end]] KnuoveUcqhyoAsh
For decrypting, add a minus sign as last argument:
% picryp $cr [string range $pi 42 end]] - Hello Tcl world
Sender and receiver must only keep the integer secret. A codebreaker can of course use brute force and try all substrings of the pi digits (of course, millions of them are available on the Web) until the decrypted result makes sense, so best use this only as a wrapper around some other encryption...