ASM Community

Hi,

I found this XTEA (m)asm implementation from http://www.simonshepherd.supanet.com/tea.htm and I have added some code  to make it run (basicly the main proc). Now i'm wondering if somebody could confirm me that the algo is really providing  correct results?

Best regards,
Sami

.486
.MODEL		FLAT, STDCALL
option		casemap:none

include		d:\masm32\include\windows.inc
include		d:\masm32\include\kernel32.inc
include		d:\masm32\include\advapi32.inc
include		d:\masm32\include\user32.inc
include		d:\masm32\include\masm32.inc
includelib	d:\masm32\lib\kernel32.lib
includelib	d:\masm32\lib\advapi32.lib
includelib	d:\masm32\lib\user32.lib
includelib	d:\masm32\lib\masm32.lib


Main						PROTO
XTEA_Encipher				PROTO
XTEA_Decipher				PROTO

CTEXT MACRO text:VARARG
    LOCAL TxtName
    .data
     TxtName BYTE text,0
    .code
  EXITM <ADDR TxtName>
ENDM

.const
Delta	equ		09E3779B9h		; Delta
DIS		equ		0C6EF3720h		; Initial value of sum in decipher routine
N		equ		32				; n (number of iterations)

.data

v		dd 0, 0
w		dd ?, ?					; Results
k		dd 0,0,0,0	; Key
Password	db "1234567890123456"

PlainText	db "aaaaaaaa", 0

.data?
.code
Start:
	invoke	Main
	invoke	ExitProcess, eax
	
Main proc
LOCAL szTmp[1024] :BYTE
LOCAL szHex1[12] :BYTE
LOCAL szHex2[12] :BYTE

	invoke	StdOut, CTEXT("XTEA Test", 13, 10)

;	invoke	MemCopy, ADDR Password, ADDR k, 16
	
	invoke	MemCopy, ADDR PlainText, ADDR v, 8

	invoke	XTEA_Encipher
	invoke	dw2hex, DWORD PTR , ADDR szHex1
	invoke	dw2hex, DWORD PTR  + 4, ADDR szHex2
	invoke	wsprintf, ADDR szTmp, CTEXT("%s %s"), ADDR szHex1, ADDR szHex2
	invoke	StdOut, ADDR szTmp
	xor		eax, eax

Exitus:
	ret
Main endp

XTEA_Encipher	proc

		PUSHAD					; Save registers

		MOV	EAX, v[0 * 4]		; EAX -> y
		MOV	EBX, v[1 * 4]		; EBX -> z
		MOV	ECX, N				; ECX -> n
		XOR	EDX, EDX			; EDX -> sum

		EnStart:

		MOV	ESI, EBX
		MOV	EDI, ESI

		SHL	ESI, 4				; z << 4
		SHR	EDI, 5				; z >> 5
		XOR	EDI, ESI			; z << 4 ^ z >> 5
		ADD	EDI, EBX			; (z << 4 ^ z >> 5) + z

		MOV	ESI, EDX
		AND	ESI, 3				; sum & 3
		MOV	ESI, k		; k
		ADD	ESI, EDX			; sum + k
		XOR	ESI, EDI			; (z << 4 ^ z >> 5) + z ^ sum + k
		ADD	EAX, ESI			; y += (z << 4 ^ z >> 5) + z ^ sum + k

		ADD	EDX, Delta			; sum += delta

		MOV	ESI, EAX
		MOV	EDI, ESI

		SHL	ESI, 4				; y << 4
		SHR	EDI, 5				; y >> 5
		XOR	EDI, ESI			; y << 4 ^ y >> 5
		ADD	EDI, EAX			; (y << 4 ^ y >> 5) + y

		MOV	ESI, EDX
		SHR	ESI, 11				; sum >> 11
		AND	ESI, 3				; sum >> 11 & 3
		MOV	ESI, k		; k
		ADD	ESI, EDX			; sum + k
		XOR	ESI, EDI			; (y << 4 ^ y >> 5) + y ^ sum + k;
		ADD	EBX, ESI			; z += (y << 4 ^ y >> 5) + y ^ sum + k;

		LOOP	EnStart

		MOV	w[0 * 4], EAX
		MOV	w[1 * 4], EBX

		POPAD					; Restore registers
		RET

XTEA_Encipher	endp

XTEA_Decipher	proc

		PUSHAD					; Save registers

		MOV	EAX, v[0 * 4]		; EAX -> y
		MOV	EBX, v[1 * 4]		; EBX -> z
		MOV	ECX, N				; ECX -> n
		MOV	EDX, DIS			; EDX -> sum

		DeStart:

		MOV	ESI, EAX
		MOV	EDI, ESI

		SHL	ESI, 4				; y << 4
		SHR	EDI, 5				; y >> 5
		XOR	EDI, ESI			; y << 4 ^ y >> 5
		ADD	EDI, EAX			; (y << 4 ^ y >> 5) + y

		MOV	ESI, EDX
		SHR	ESI, 11				; sum >> 11
		AND	ESI, 3				; sum >> 11 & 3
		MOV	ESI, k		; k
		ADD	ESI, EDX			; sum + k
		XOR	ESI, EDI			; (y << 4 ^ y >> 5) + y ^ sum + k
		SUB	EBX, ESI			; z -= (y << 4 ^ y >> 5) + y ^ sum + k

		SUB	EDX, Delta			; sum -= delta

		MOV	ESI, EBX
		MOV	EDI, ESI

		SHL	ESI, 4				; z << 4
		SHR	EDI, 5				; z >> 5
		XOR	EDI, ESI			; z << 4 ^ z >> 5
		ADD	EDI, EBX			; (z << 4 ^ z >> 5) + z

		MOV	ESI, EDX
		AND	ESI, 3				; sum & 3
		MOV	ESI, k		; k
		ADD	ESI, EDX			; sum + k
		XOR	ESI, EDI			; (z << 4 ^ z >> 5) + z ^ sum + k
		SUB	EAX, ESI			; y -= (z << 4 ^ z >> 5) + z ^ sum + k

		LOOP	DeStart

		MOV	w[0 * 4], EAX
		MOV	w[1 * 4], EBX

		POPAD					; Restore registers
		RET

XTEA_Decipher	endp

end Start

Thank you f0dder, you are a life saver!

I spent countles of hours googling around without founding how can I verify that this algo gives correct results and now it's proven.