GetSmart Block Cipher

[xcoder]

print "###################################"

global two32,kky1,kky2,kky3 '************

two32 = 2^32

key = 2654435769

kky1 = leftrotate(key,1)

kky2 = leftrotate(key,4)

kky3 = leftrotate(key,10)

dim B(4)

msg$ = "The quick brown fox jumps over the lazy dogs back";chr$(13)+_

"Testing the GetSmart block cipher in JustBasic 2.0"

print msg$

print "Length of message is ";len(msg$)

for i = 1 to len(msg$) step 4

chunk$ = mid$(msg$,i,4)

x = len(chunk$)

if x < 4 then chunk$ = chunk$ + extra$(chunk$,x)'pad the final block

k = 3 'array index

for j = 1 to len(chunk$)

ascii = asc(mid$(chunk$,j,1))

B(k) = ascii ' fill array B

k = k - 1

next j

a = B(3) * 256^3 '4 byte block

b = B(2) * 256^2

c = B(1) * 256^1

d = B(0) * 256^0

sum = a + b + c + d

numCrypt = Encrypt(sum)

result$ = result$ + dec2Text$(numCrypt)

next i

print result$

'==================================================================

print ""

input "Press Enter to Decrypt Message >> ";entry$

msg$ = result$

print ""

for i = 1 to len(msg$) step 4

chunk$ = mid$(msg$,i,4)

k = 3 'array index

for j = 1 to len(chunk$)

ascii = asc(mid$(chunk$,j,1))

B(k) = ascii ' fill array B

k = k - 1

next j

a = B(3) * 256^3 '4 byte block

b = B(2) * 256^2

c = B(1) * 256^1

d = B(0) * 256^0

sum = a + b + c + d

numCrypt = Decrypt(sum)

plain$ = plain$ + dec2Text$(numCrypt)

next i

print plain$


print:print

print "End of Code"

End





function extra$(a$,x) 'pads the final text block

if x < 4 then

dif = 4 - x

for i = 1 to dif

pad$ = pad$ + chr$(128)

next i

end if

extra$ = pad$

end function




function Encrypt(a)

print

f = a xor 2^32-1 'invert all bits

ff = f xor kky1 'use 1st sub key

print ff,decHex$(ff),dec2Bin$(ff)

Encrypt = Round2(ff)

end function



function Round2(a)

f = a xor kky2 'use 2nd sub key

print f,decHex$(f),dec2Bin$(f)

Round2 = Round3(f)

end function



function Round3(a)

f = a xor kky3 'use 3rd sub key

print f,decHex$(f),dec2Bin$(f)

Round3 = f:print

end function


print "===================================================="


function Decrypt(a)

print

f = a xor kky3 'reverse order of sub keys

print f,decHex$(f),dec2Bin$(f)

Decrypt = revRound2(f)

end function


function revRound2(a)

f = a xor kky2

print f,decHex$(f),dec2Bin$(f)

revRound2 = revRound3(f)

end function



function revRound3(a)

f = a xor kky1

ff = f xor 2^32-1 'invert all bits

print ff,decHex$(ff),dec2Bin$(ff)

revRound3 = ff

end function





' leftrotate: spins bits left n times

function leftrotate(num,times)

num=num mod two32

r = (num*2^times) mod two32 '************

l = int(num/(2^(32-times)))

leftrotate = r+l

end function





function dec2Text$(dec) 'outputs cipher text and plain text

hex$ = decHex$(dec)

for i = 1 to len(hex$)step 2

chunk$ = mid$(hex$,i,2)

ascii = hexDec(chunk$)

char$ = char$ + chr$(ascii)

next i

dec2Text$ = char$

end function





function dec2Bin$(num)

dec2Bin$ =""

while (num >0)

dec2Bin$ =str$( num mod 2) +dec2Bin$

num =int(num /2)

wend

dec2Bin$ =right$( "00000000" +dec2Bin$, 32)

end function