Bacon cipher: Difference between revisions

=={{header|Lua}}==

<lang Lua>

function Bacon( txt, secret, e )

local alpha = {}, t

function toBits( num, bits )

local t, s = "", 0

for b = bits, 1, -1 do

s = math.fmod( num, 2 )

t = s .. t

num = math.floor( num / 2 )

end

return t

end

function find( a, arr )

for i = 1, #arr do

if arr[i] == a then return i end

end

return -1

end

function toAlpha( secret )

local str, z = "", 0

secret = secret:upper()

for i = 1, string.len( secret ) do

z = secret:sub( i, i )

if z < 'A' or z > 'Z' then

str = str .. alpha[27]

else

k = z:byte( 1 ) - 65 + 1

str = str .. alpha[k]

end

end

return str

end

function fromAlpha( secret )

local l, msg, c, idx = secret:len(), "", 0, 0

if math.fmod( l, 5 ) ~= 0 then

print( "Message length does not match!" )

return

end

for i = 1, l, 5 do

c = secret:sub( i, i + 4 )

idx = find( c, alpha )

if idx > 0 then

if idx == 27 then

msg = msg .. " " -- unknown char - add space

else

msg = msg .. string.char( 64 + idx )

end

end

end

return msg

end

function encode( txt, secret )

local sec, encoded, idx = toAlpha( secret ), "", 0

if sec:len() > txt:len() then

print( "Text is too short!" )

return

end

txt = txt:lower()

for i = 1, string.len( sec ) do

t = txt:sub( idx, idx )

while( t < 'a' or t > 'z' ) do

encoded = encoded .. t

idx = idx + 1

t = txt:sub( idx, idx )

end

idx = idx + 1

if sec:sub( i, i ) == '1' then

encoded = encoded .. string.char( t:byte(1) - 32 )

else

encoded = encoded .. t

end

end

return encoded

end

function decode( txt )

local secret, c = "", 0

for i = 1, string.len( txt ) do

c = txt:sub( i, i )

if not( c < 'a' and ( c < 'A' or c > 'Z' ) or c > 'z' ) then

local s = 0

if c == c:upper() then s = 1 end

secret = secret .. s

end

end

return fromAlpha( secret )

end

-- create alphabet

for i = 0, 26 do

t = ( toBits( i, 5 ) )

alpha[#alpha + 1] = t

end

-- encode or decode

if e == 1 then

return encode( txt, secret )

elseif e == 0 then

return decode( secret )

end

end

local a = Bacon( "one morning, when gregor samsa woke from troubled dreams"..

", he found himself transformed in his bed into a horrible "..

"vermin. he lay on his armour-like back, and if he lifted "..

"his head a little he could see his brown belly, slightly "..

"domed and divided by arches into stiff sections.",

"This is a Bacon cipher test", 1 )

print( a )

print( Bacon( "", a, 0 ) )

</lang>

{{out}}

<pre>

sh-4.3$ lua main.lua

One MOrnING, wHen gRegOr SAmSa wOke fRom TrOUbLed dreaMS, hE found Himself trAnsFORmeD In HIS bEd intO a hOrribLE VErmIN.

He lAy oN his ARMoUr-LikE BacK, anD if He LifTE

THIS IS A BACON CIPHER TEST

</pre>