; Tiny Encryption Algorithm
; A public domain block cipher by David Wheeler and Roger Needham
; 80386 assembly implementation by Fauzan Mirza
; TEA uses a 128 bit key and operates on 64 bit data blocks
.model tiny
.code
.386
org 100h
Start:
mov si,offset Key
mov di,offset Data
call Encrypt
mov si,offset Key
mov di,offset Data
call Decrypt
ret
Key:
db "0000","0000","0000","0000"
Data:
db "0000","0000"
sum equ eax
y equ ebx
z equ ecx
delta equ edx
rounds equ di
t equ ebp
v0 equ dword ptr [di]
v1 equ dword ptr [di+4]
k0 equ dword ptr [si]
k1 equ dword ptr [si+4]
k2 equ dword ptr [si+8]
k3 equ dword ptr [si+12]
Encrypt:
push di
mov y,v0
mov z,v1
xor sum,sum
mov delta,9e3779b9h ; sqr(5)-1 * 2^31
mov rounds,32
ELoopR:
add sum,delta
mov t,z
shl t,4
add y,t
mov t,k0
xor t,z
add y,t
mov t,z
shr t,5
xor t,sum
add y,t
add y,k1
;
mov t,y
shl t,4
add z,t
mov t,k2
xor t,y
add z,t
mov t,y
shr t,5
xor t,sum
add z,t
add z,k3
dec rounds
jnz ELoopR
pop di
mov v0,y
mov v1,z
ret
Decrypt:
push di
mov y,v0
mov z,v1
mov delta,9e3779b9h ; sqr(5)-1 * 2^31
mov sum,delta
shl sum,5
mov rounds,32
DLoopR:
mov t,y
shl t,4
sub z,t
mov t,k2
xor t,y
sub z,t
mov t,y
shr t,5
xor t,sum
sub z,t
sub z,k3
;
mov t,z
shl t,4
sub y,t
mov t,k0
xor t,z
sub y,t
mov t,z
shr t,5
xor t,sum
sub y,t
sub y,k1
sub sum,delta
dec rounds
jnz DLoopR
pop di
mov v0,y
mov v1,z
ret
end Start
