Herbert Kleebauer wrote:
> jella_flores@[EMAIL PROTECTED]
wrote:
>
> > hi to everyone,
> > i'm posting here in hope to find help for my troubles in tracing the
> > code line by line...i cannot go on finding the exact string that this
> > program requires...i want to track line by line but my problem is,i
> > dont know how to follow the codes...i only understand few instructions
> > and though i am familiar with all the instructions,i dont know how to
> > understand it if it in a code being applied...please help me by
> > commenting the codes...or if you can do better,please?i beg you
> > guys...more power to you all!
> > i just want some sample how to trace...
>
> You better ask in alt.lang.asm or comp.lang.asm.x86 where such
> programs have been discussed a few days ago. But you can tell
> your teacher, he will not get a good grade for this program
> (at least if it was written in assembler and not in a HLL).
> Here a maybe better understandable disassembly:
>
>
>
> key1=$cefa
> key2='.'
>
> @[EMAIL PROTECTED]
> br.w begin
>
> ; encrypted message
> dat: dc.b 'Y' ^ key1 &$ff
> dc.b 'o' ^ key1 >>8
> dc.b 'u' ^ key1 &$ff
> dc.b "'" ^ key1 >>8
> dc.b 'v' ^ key1 &$ff
> dc.b 'e' ^ key1 >>8
> dc.b ' ' ^ key1 &$ff
> dc.b 'g' ^ key1 >>8
> dc.b 'o' ^ key1 &$ff
> dc.b 't' ^ key1 >>8
> dc.b ' ' ^ key1 &$ff
> dc.b 'i' ^ key1 >>8
> dc.b 't' ^ key1 &$ff
> dc.b ' ' ^ key1 >>8
> dc.b 'r' ^ key1 &$ff
> dc.b 'i' ^ key1 >>8
> dc.b 'g' ^ key1 &$ff
> dc.b 'h' ^ key1 >>8
> dc.b 't' ^ key1 &$ff
> dc.b '!' ^ key1 >>8
> dc.b '!' ^ key1 &$ff
> dc.b '!' ^ key1 >>8
> dc.b ' ' ^ key1 &$ff
> dc.b 'I' ^ key1 >>8
> dc.b ' ' ^ key1 &$ff
> dc.b 'h' ^ key1 >>8
> dc.b 'o' ^ key1 &$ff
> dc.b 'p' ^ key1 >>8
> dc.b 'e' ^ key1 &$ff
> dc.b ' ' ^ key1 >>8
> dc.b 'y' ^ key1 &$ff
> dc.b 'o' ^ key1 >>8
> dc.b 'u' ^ key1 &$ff
> dc.b "'" ^ key1 >>8
> dc.b 'l' ^ key1 &$ff
> dc.b 'l' ^ key1 >>8
> dc.b ' ' ^ key1 &$ff
> dc.b 'p' ^ key1 >>8
> dc.b 'a' ^ key1 &$ff
> dc.b 's' ^ key1 >>8
> dc.b 's' ^ key1 &$ff
> dc.b ' ' ^ key1 >>8
> dc.b 't' ^ key1 &$ff
> dc.b 'h' ^ key1 >>8
> dc.b 'e' ^ key1 &$ff
> dc.b ' ' ^ key1 >>8
> dc.b 't' ^ key1 &$ff
> dc.b 'e' ^ key1 >>8
> dc.b 'c' ^ key1 &$ff
> dc.b 'h' ^ key1 >>8
> dc.b 'n' ^ key1 &$ff
> dc.b 'i' ^ key1 >>8
> dc.b 'c' ^ key1 &$ff
> dc.b 'a' ^ key1 >>8
> dc.b 'l' ^ key1 &$ff
> dc.b ' ' ^ key1 >>8
> dc.b 'e' ^ key1 &$ff
> dc.b 'x' ^ key1 >>8
> dc.b 'a' ^ key1 &$ff
> dc.b 'm' ^ key1 >>8
> dc.b '.' ^ key1 &$ff
> dc.b '.' ^ key1 >>8
> dat62: dc.b key2^ key1 &$ff
> dc.b '$' ^ key1 >>8
> dat_end:
>
> inbuf: blk.b 15,$24 ; 15 byte input buffer
> msg1: dc.b "Enter the password: $"
> msg2: dc.b "Don't push it...exciting...$"
>
> begin: move.w #msg1,r1
> move.b #9,m0 ; print message1
> trap #$21
>
> eor.w r5,r5
> input: move.b #1,m0
> trap #$21
> cmp.b #13,r0 ; <RETURN>?
> beq.b process ; yes, then exit input routine
> move.b r0,inbuf(r5.w) ; store in input buffer
> inc.w r5
> cmpq.w #10,r5 ; 10 bytes read?
> beq.b wrong ; yes, that's too much
> br.b input ; read next character
>
> process:bclr.w #10,sr ; clear direction flag
> move.w #dat,r5 ; pointer to dat
> move.w r5,r6 ; pointer to dat
> move.w #dat_end,r2
> sub.w r5,r2 ; size of encrypted data in byte
> lsr.w #1,r2 ; size of encrypted data in word
>
> _10: move.w (r5.w)+-,r0 ; read next word from data
> eor.w #key1,r0 ; decrypt it
> move.w r0,(r6.w)+-{s1} ; store it back
> dbf.w r2,_10 ; loop until complete data processed
>
> move.b #0,r0
> move.w #dat_end,r3
> subq.w #2,r3 ; pointer to dat62
> move.b (r3.w,r0.b),r0 ; dat62 = key2
> move.b r0,r1 ; dat62
>
> move.w #pass_end,r5
> subq.w #pass_length,r5 ; pointer to pass
> move.w r5,-(sp)
> move.w r5,r6
> move.w #10,r2 ; prozess pass0 - pass9
>
> _20: move.b (r5.w)+-,r0 ; get next byte of pass
> eor.b r1,r0 ; eor it with dat62
> move.b r0,(r6.w)+-{s1} ; store it back
> dbf.w r2,_20 ; loop until dat62 processed
>
> move.w #10,r2 ; compare 10 bytes
> move.w (sp)+,r5 ; pointer to pass
> move.w #inbuf,r6 ; pointer to input input string
>
> repeq_r2 cmp.b (r6.w)+-{s1},(r5.w)+- ; compare
> bne.b wrong ; strings not equal
> move.w #dat,r1 ; decrypted text
> move.b #$09,m0 ; print it
> trap #$21
> br.b byebye ; exit
> nop
>
> wrong: move.w #msg2,r1
> move.b #$09,m0 ; print message2
> trap #$21
> br.b byebye ; exit
> nop
>
> pass: dc.b 'J' ^ key2
> dc.b 'o' ^ key2
> dc.b 'h' ^ key2
> dc.b 'n' ^ key2
> dc.b ' ' ^ key2
> dc.b '3' ^ key2
> dc.b ':' ^ key2
> dc.b '1' ^ key2
> dc.b '6' ^ key2
> dc.b '$' ^ key2
> dc.b 0
> pass_end:
> pass_length=pass_end-pass
>
> byebye: move.w #$4c00,r0
> trap #$21
Good luck to jella deciphering this one!
|
