Lately I've been working on my own implementation of the Tiny Encryption Algorithm. What is the Tiny Encryption Algorithm? WikiPedia answers, "The Tiny Encryption Algorithm (TEA) is a block cipher notable for its simplicity of description and implementation (typically a few lines of code)." Well, I've written my own implentation in assembly, enjoy.

In WikiPedia's example, the encrypt() routine looks like the following:

void encrypt (unsigned long* v, unsigned long* k) {
    unsigned long v0=v[0], v1=v[1], sum=0, i;           /* set up */
    unsigned long delta=0x9e3779b9;                     /* a key schedule constant */
    unsigned long k0=k[0], k1=k[1], k2=k[2], k3=k[3];   /* cache key */
    for (i=0; i < 32; i++) {                            /* basic cycle start */
        sum += delta;
        v0 += ((v1<<4) + k0) ^ (v1 + sum) ^ ((v1>>5) + k1);
        v1 += ((v0<<4) + k2) ^ (v0 + sum) ^ ((v0>>5) + k3);  /* end cycle */
    }
    v[0]=v0; v[1]=v1;
}

Only ~10 lines, not bad. My implementation of the above in Intel Architecture 32-bit (IA32) Assembly came out as follows:

; tea.asm
; By Charles Hooper <hoopercharles@gmail.com>
;
; Tiny Encryption Algorithm implementation
;
 
section .data
	delta	dd	0x9e3779b9	; Magic constant
	sum	dd	0
	counter dd	0
 
section .bss
	v0:	resb	4	; 64-bit (2x32) block to encrypt
	v1:	resb	4
 
	k0:	resb	4	; 128-bit (4x32) key
	k1:	resb	4
	k2:	resb	4
	k3:	resb	4
 
section .text
	global main	; gcc entry point
 
main:
        push    ebp		; set up stack frame -- What?
	mov	ebp,esp		; again, what?
 
	;; Set up variables -- For simplicity, you could set your key and data you want to encrypt here.
	mov	dword [v0],0
	mov	dword [v1],0
	mov	dword [k0],0
	mov	dword [k1],0
	mov	dword [k2],0
	mov	dword [k3],0
 
tea_encrypt_loop:
	cmp	dword [counter],20h	; loop while counter < 32 (20h)
	je	near exit_tea_encrypt_loop
 
	mov	eax,[sum]	; sum += delta
	add	eax,[delta]
	mov	[sum],eax
 
	;; v0 += ((v1<<4) + k0) ^ (v1 + sum) ^ ((v1>>5) + k1)
	xor	eax,eax
	xor	ebx,ebx
 
	mov	eax,[v1]
	shl	eax,4
	add	eax,[k0]
 
	mov	ebx,[v1]
	add	ebx,[sum]
 
	xor	eax,ebx
 
	mov	ebx,[v1]
	shr	ebx,5
	add	ebx,[k1]
 
	xor	eax,ebx
 
	add	[v0],eax
	;; End
 
	;; v1 += ((v0<<4) + k2) ^ (v0 + sum) ^ ((v0>>5) + k3)
	xor	eax,eax
	xor	ebx,ebx
 
	mov	eax,[v0]
	shl	eax,4
	add	eax,[k2]
 
	mov	ebx,[v0]
	add	ebx,[sum]
 
	xor	eax,ebx
 
	mov	ebx,[v0]
	shr	ebx,5
	add	ebx,[k3]
 
	xor	eax,ebx
 
	add	[v1],eax
	;; End
 
	inc	dword [counter]
 
jmp	tea_encrypt_loop
 
exit_tea_encrypt_loop:
exit:
	mov esp,ebp
	pop ebp
 
	xor eax,eax		; exit(0)
	ret

It's a bit longer @ 92 lines including blank lines, but it works just as well! If you notice anything wrong, please leave a comment and let me know.