Cracking 1

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Text File | 2001-12-15 | 14.8 KB | 281 lines

;; ;; aPLib compression library - the smaller the better :) ;; ;; NASM 16bit assembler tiny depacker example ;; ;; Copyright (c) 1998-2000 by Joergen Ibsen / Jibz ;; All Rights Reserved ;; ;; -> 16bit by METALBRAIN (metalb@bart.us.es) ;; org 256 cld ;Clear direction flag for safety mov ah,4ah ;Modify memory block size (on start, ; the .COM program is given all free ; memory, but this could be less than ; the needed amount (162K). As a nice ; side effect, we are freeing unused ; memory, but who cares under DOS? mov bh,41 ;Number of needed paragraphs ; (rounded up) call int_n_check ;Resize or exit if error mov si,129 ;Arguments from PSP start here mov di,testitnow ;This will be called quite a few times ; and later will be used to place ; variables space1 call di ;Parse... jz space1 ;Search for non-space dec si ;Found: here start infile name mov dx,si ;Keep it in DX space2 call di ;Keep parsing jnz space2 ;Till a space appears mov [si-1],dh ;Make infile ASCIIZ space3 call di jz space3 ;Now search a non-space again dec si ;Here start outfile name push si ;Keep it in stack space4 lodsb ;Final parse cmp al," " ja space4 ;Space or below means end of filename mov [si-1],dh ;Make ASCIIZ this one too mov ax,3d00h ;Function to open infile call int_n_check ;Try it stosw ;Store infile handle at handlein mov dx,tmpname xor cx,cx mov ah,3ch call int_n_check ;Create temporal outfile: "NOT OK$" stosw ;Store temporal outfile handle xchg ax,dx ;And place it in DX xor ebx,ebx ;EBX=0 pop si ;Pop outfile name address from stack mov bh,8 ;BX=inbuff mov esp,ebx ;Set stack before inbuff mov bx,es ;Segment add bh,8 ; +32K imul eax,ebx,byte 16 ;32 bit start of segment address+32K add eax,esp ;EAX=freemem 32 bit address push si ;Push again outfile name address push dx ;Also store temporal outfile handle mov dl,128 ;Reset bit counter in DL, and DX=0080h mov cl,3 ;Set EAX at freemem32, origin32 and rep stosd ; limit32 add [di-2],byte 2 ;Now limit32=freemem32+128K add [di-7],dx ;Now origin32=freemem32+32K xchg eax,edi ;Set freemem32 at EDI mov esi,edi ;And ESI ;Starting point for DEPACK16 push edi ;Store freemem32 literal call getesi ;Copy a byte from [esi] to [edi] putedi_nexttag call putedi call newtest ;Here EAX=0 jmp short nexttag ;Skip next part normalcodepair xchg ax,cx ;High part of distance in AX dec ax ;Subtract 1. Min value is 0 shl eax,8 ;EAX=00dddd00h call getesi ;Fill distance in AL call getgamma ;Take gamma encoded ECX cmp eax,32000 jae domatch_with_2inc ;Above 31999: ECX+=2 cmp ah,5 jae domatch_with_inc ; 1279<EAX<32000: ECX=+1 cmp ax,byte 127 ja domatch ;EAX<128: ECX+=2 domatch_with_2inc inc ecx domatch_with_inc inc ecx domatch xchg eax,ebp ;Store EAX in EBP domatch_R0 mov eax,ebp ;Take EAX from last EBP domatch_continue ;Here EAX=match distance ; ECX=match lenght push esi ;Store current read pointer mov esi,edi sub esi,eax ;ESI=EDI-EAX > origin pointer cmp esi,[freemem32] ;Test for bad infile #1: Limit crossed call finerr01 ;Exit if error repmovsb call dontread ;getesi without checking limit call putedi ;and with putedi completes the movsb mov ah,128 ;Here EAX=32768 (in case of writing call newtest ; data, update esi too) loop repmovsb,ecx ;Do it ecx times pop esi ;Recover read pointer nexttag call getbit ;Get a bit jnc literal ;0: literal, go for it xor ecx,ecx ;Clear ECX xor ax,ax ;and AX call getbit ;Get another bit jnc codepair ;10: codepair, go for it call getbit ;Get yet another one jnc shortmatch ;110: shortmatch mov al,16 ;Set marker bit inc cx ;CX=1 getmorebits call getbit ;Get a bit adc al,al ;Set it in AL jnc getmorebits ;Do it till marker is out (4 times) jnz domatch_continue ; 111xxxx > continue, AL has distance jmp short putedi_nexttag ;1110000: Put a zero byte codepair call getgamma ;Get gamma encoded first part of ; distance in CX. Min value is 2 dec cx ;\Subtract 2, if not zero then loop normalcodepair ;/continue with distance push word domatch_R0 ;Get gamma encoded lenght in ECX then ; jump to domatch_R0 (use last ; distance) getgamma inc cx ;First bit is always 1 getgammaloop call getbit ;Get next bit adc ecx,ecx ;Put it in ECX call getbit ;Get gamma bit jc getgammaloop ;If it's 1, continue growing ECX ret shortmatch call getesi ;Get a byte shr ax,1 ;Distance = AL/2, Lenght in carry flag jz donedepacking ;If zero, end packing adc cx,cx ;Lenght = 1 or 0 jmp short domatch_with_2inc ; Decode with lenght 2 or 3 donedepacking pop esi ;ESI=freemem32 pop bx ;Get outfile handle sub edi,esi ;And here finish DEPACK 16 ;Now edi has the number of depacked ; bytes left to be written push ds ;Preserve data segment mov ch,080h ;Write using 32K chunks to enable ; the sign optimization mov dx,freemem ;Flush everything from here to end more cmp edi,ecx ja notlast ;If EDI > 32K, write 32K bytes mov cx,di ;If EDI < 32K, write EDI bytes notlast call writefile ;Write chunk mov ax,ds add ah,8 mov ds,ax ;Advance 32K sub edi,ecx ;Update number of bytes to be written ja more ;Above zero, continue writing pop ds ;Recover data segment push ds pop es ;Set es=ds pop dx ;Get pointer to outfile name call close_del ;Close temporal outfile and try to ; delete the file named with our ; outfile name, in case it exists jnc renameit ;If that file existed and was deleted, ; go ahead and rename the temporal one cmp al,5 ;If it didn't exist, rename it too jz finerr ;But if error was for other reason, ; exit with NOT OK renameit mov ah,56h mov di,dx mov dx,tmpname call int_n_check ;Rename temporal outfile to outfile mov dx,noerr ;Final message: OK final_dxok mov ah,9 int 33 ;Show final message int 20h ;Exit program writefile mov ah,40h call int_n_check ;Write dec ax jns not_finerr ;If disk isn't full there's no error finerr mov dx,tmpname ;Error message: NOT OK push word final_dxok ;Return point close_del mov ah,3eh int 33 ;Close temporal outfile mov ah,41h int 33 ;Delete outfile (when called to ; close_del) or temporal outfile not_finerr ret ; (when we fall from finerr) getesi cmp esi,[freemem32] ; If esi is at freemem32, we must jnz dontread ;load 32k of compressed data pushad ;Keep all registers (32bit because mov ah,3fh ; DOS function may modify EAX!!!) mov bx,[handlein] ;Take infile handle mov cx,32768 ;Number of bytes mov dx,inbuff ;Place to read call int_n_check ;Read and exit if error dec ax ;---Test for bad infile #2: 0 bytes popad ;\/ read (a good infile will finish js finerr ;/\ and won't ask for more data) ; >Restore registers sub esi,32768 ;esi at beginning of buffer again dontread push esi ;----->Emulates mov al,[esi] in 16 bit pop bx ; / code (as mov al,[esi] gives pop bx ; / a nasty fault) ror bx,4 ; / mov es,bx ; / mov al,[es:si] ;/ inc esi ;Update read pointer ret int_n_check int 33 ;Perform operation (depends on AH) finerr01 jc finerr ;If it failed, exit with NOT OK ret getbit add dl,dl ;Get a tag bit jnz stillbitsleft ;If zero, that bit was the marker, so ; we must read a new tag byte from xchg ax,dx ;\ the infile buffer call getesi ; >Emulate mov dl,[esi], inc esi xchg ax,dx ;/ stc ;Carry flag is end marker adc dl,dl ;Get first bit and set marker stillbitsleft ret ;Return with bit read in flag C newtest cmp edi,[limit32] ;Check if we've run out of memory jc endtest ;NO: end test pushad ;Keep registers mov dx,freemem mov cx,32768 mov bx,[handletmp] call writefile ;Write 32K of data mov ecx,edi mov esi,[origin32] sub ecx,esi ;ECX=number of bytes to be moved mov edi,[freemem32] ;Output data will be moved 32K back otherrepmovsb call getesi ; \ call putedi ; >Emulates rep movsb loop otherrepmovsb,ecx ;/ popad ;Restore registers sub esi,eax ;Update read pointer (sub 32K if ; we are in the repmovsb loop) mov ah,128 ;EAX=32K sub edi,eax ;Update write pointer endtest ret putedi push edi ;----->Emulate mov [edi],al in 16 bit pop bx ; / code (as mov [edi],al gives pop bx ; / a nasty fault) ror bx,4 ; / mov es,bx ; / mov [es:di],al ;/ inc edi ;Update write pointer xor eax,eax ;Clear EAX ret tmpname db "NOT " noerr db "OK$",0 testitnow lodsb ;Parse one byte cmp al,32 ;Is it space? jc finerr01 ;Below space: bad arguments > exit ret handlein EQU testitnow handletmp EQU testitnow+2 freemem32 EQU testitnow+4 origin32 EQU testitnow+8 limit32 EQU testitnow+12 ;Stack is between program and 1280 inbuff EQU 2048 ;Place for 32K infile reading buffer freemem EQU inbuff+32768