Tiny Encryption Algorithm TEA (Complete)

[xcoder]

'128 bit key/16 bytes

print "Four 32 bit/4 byte keys"



k0 = K(0)

k1 = K(1)

k2 = K(2)

k3 = K(3)

'bit shifting variables

v0sL4 = shiftL(v0,4)

v1sL4 = shiftL(v1,4)

v0sR5 = shiftR(v0,5)

v1sR5 = shiftR(v1,5)



'---------------------------------------------------------

call keys

text$ = "the quick brown fox jumps over the lazy dogs back"

print "the message length is ";len(text$)

print "input data blocks"



ctr = 1

for i = 1 to len(text$) step 8 '8 characters per block

block$ = mid$(text$,i,8)

call text2Dec block$,ctr

ctr = ctr + 1

next

print ""

print "Encrypted data blocks"

for i = 1 to ctr

print E1(i),E2(i)

next

'The contents of E1 and E2 Numeric arrays

'are written to a file.

print ""



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

j = 1

do while j < ctr

'loop output of E array into Decrypt procedure

'Simulates reading the Numeric contents of a file

'one line at a time into arrays D1 and D2

v0 = E1(j)

v1 = E2(j)

call Decrypt v0,v1,j

j = j + 1

loop

print ""

'---------------------------------------------------

for j = 1 to ctr 'number of data blocks

print D1(j),D2(j) 'display D array (Decrypt)

a = D1(j)

b = D2(j)

hex1$ = decHex$(a)

hex2$ = decHex$(b)

double$ = hex1$ + hex2$

hex3$ = hex3$ + double$

next j

for i = 1 to len(hex3$)step 2

chunk$ = mid$(hex3$,i,2)

ascii = hexdec(chunk$)

char$ = char$ + chr$(ascii)

next i

print char$



print:print

print "End of Code"

End





sub keys

randomize 0.22

for i = 0 to 3

x = int(rnd(1)* 2^32)

K(i) = x

print K(i)

next

print ""

end sub



sub text2Dec block$,ctr

x = len(block$)

if x < 8 then block$ = block$ + extra$(block$,x) 'pad the final block

sideL$ = left$(block$,4)

sideR$ = right$(block$,4)

x = 3 'initialize down counter for 4 byte array

for i = 1 to len(sideL$)

byte = asc(mid$(sideL$,i,1))

A(x) = byte * 256^x

word0 = word0 + A(x)

x = x - 1

next

x = 3 'initialize down counter for 4 byte array

for i = 1 to len(sideR$)

byte = asc(mid$(sideR$,i,1))

B(x) = byte * 256^x

word1 = word1 + B(x)

x = x - 1

next

v0 = word0

v1 = word1

print v0,v1

call Encrypt v0,v1,ctr

end sub



function extra$(a$,x)

if x < 8 then

dif = 8 - x

for i = 1 to dif

pad$ = pad$ + chr$(128)

next

end if

extra$ = pad$

end function





sub Encrypt v0,v1,ctr

sum = 0 'set up;sum is zero

delta = 2654435769 'a key schedule constant (golden ratio)

for i = 0 to 3 'basic cycle start

sum = sum + delta

v0 = (v0 + (v1sL4)+ k0) xor (v1 + sum) xor (v1sR5 + k1)

v1 = (v1 + (v0sL4) + k2) xor (v0 + sum) xor (v0sR5 + k3)

next

E1(ctr) = v0

E2(ctr) = v1

end sub





sub Decrypt v0,v1,ctr

sum = 10617743076 ' set up; sum is (rounds * delta) important ***********

delta = 2654435769 ' a key schedule constant

for i = 0 to 3 ' basic cycle start

v1 = (v1 - (v0sL4) + k2) xor (v0 + sum) xor (v0sR5 + k3)

v0 = (v0 - (v1sL4) + k0) xor (v1 + sum) xor (v1sR5 + k3)

sum = sum - delta

next

D1(ctr) = v0

D2(ctr) = v1

end sub



function shiftL(b,n)

shiftL = (b *2^n) and 2^32-1

end function



function shiftR(b,n)

shiftR = int(b /2^n)

end function