.text:0804A1E8 ; Decoder: (byte-level) .text:0804A1E8 ; Pn = Cn - Cn-1 - 0x17, for n > 0 .text:0804A1E8 ; Po = Co - 0x17 .text:0804A1E8 ; .text:0804A1E8 ; => Corresponding Encoder: .text:0804A1E8 ; => Co = Po + 0x17 .text:0804A1E8 ; => Cn = Pn + Cn-1 + 0x17, for n > 0 .text:0804A1E8 ; Attributes: bp-based frame .text:0804A1E8 .text:0804A1E8 Decoder proc near ; CODE XREF: MainMonster+1D8p .text:0804A1E8 .text:0804A1E8 var_10 = byte ptr -10h .text:0804A1E8 tmpBuf_Decoder = dword ptr -4 .text:0804A1E8 Length = dword ptr 8 .text:0804A1E8 Cipher = dword ptr 0Ch .text:0804A1E8 PlainText = dword ptr 10h .text:0804A1E8 .text:0804A1E8 push ebp .text:0804A1E9 mov ebp, esp .text:0804A1EB sub esp, 4 ; Integer Subtraction .text:0804A1EE push edi .text:0804A1EF push esi .text:0804A1F0 push ebx .text:0804A1F1 mov edi, [ebp+Length] .text:0804A1F4 lea ebx, [edi-1] ; EBX = PacketSize-1 .text:0804A1F7 lea eax, [edi+3] ; //Round up to Nearest 4 bytes .text:0804A1F7 ; EAX = PacketSize+3 .text:0804A1FA and al, 0FCh ; //Round up to Nearest 4 bytes .text:0804A1FA ; PacketSize - (PacketSize%4) .text:0804A1FC sub esp, eax ; Create Stack Space for Packet .text:0804A1FE mov [ebp+tmpBuf_Decoder], esp .text:0804A201 mov al, ds:gState1 .text:0804A207 mov esi, [ebp+PlainText] .text:0804A20A mov [esi], al ; 1st Byte of Output = AL .text:0804A20A ; = (0?) byte_80675E5 .text:0804A20C test ebx, ebx ; Logical Compare .text:0804A20E jl Exit_Decoder ; Jump if Less (SF!=OF) .text:0804A20E .text:0804A214 .text:0804A214 Processing_1: ; CODE XREF: Decoder+ADj .text:0804A214 lea edx, [ebx-1] ; EBX = n .text:0804A214 ; EDX = n-1 .text:0804A217 test ebx, ebx ; Logical Compare .text:0804A219 jz short Finished_Processing ; Jump if Zero (ZF=1) .text:0804A219 .text:0804A21B mov esi, [ebp+Cipher] .text:0804A21E movzx eax, byte ptr [ebx+esi] ; EAX = C(n) .text:0804A222 movzx edx, byte ptr [edx+esi] ; EDX = C(n-1) .text:0804A226 sub eax, edx ; EAX = C(n) - C(n-1) .text:0804A228 jmp short Processing_2 ; ECX = P(n) .text:0804A228 ; =C(n)-C(n-1)-0x17 .text:0804A228 .text:0804A228 ; 컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴컴� .text:0804A22A align 4 .text:0804A22C .text:0804A22C Finished_Processing: ; CODE XREF: Decoder+31j .text:0804A22C mov esi, [ebp+Cipher] .text:0804A22F movzx eax, byte ptr [esi] ; Move with Zero-Extend .text:0804A232 .text:0804A232 Processing_2: ; CODE XREF: Decoder+40j .text:0804A232 lea ecx, [eax-17h] ; ECX = P(n) .text:0804A232 ; =C(n)-C(n-1)-0x17 .text:0804A235 test ecx, ecx ; Logical Compare .text:0804A237 jge short if_positive ; Jump if Greater or Equal (SF=OF) .text:0804A237 .text:0804A239 .text:0804A239 if_negative: ; NOP .text:0804A239 lea esi, [esi+0] .text:0804A23C .text:0804A23C until_positive: ; CODE XREF: Decoder+5Aj .text:0804A23C add ecx, 100h ; P(n) = P(n)%0x100 .text:0804A242 js short until_positive ; P(n) = P(n)%0x100 .text:0804A242 .text:0804A244 .text:0804A244 if_positive: ; CODE XREF: Decoder+4Fj .text:0804A244 xor edx, edx ; Logical Exclusive OR .text:0804A246 cmp edx, edi ; Is EDI = PacketSize = 0? .text:0804A248 jge short Decoder_Bytes ; Pn = Cn - Cn-1 - 0x17 .text:0804A248 .text:0804A24A .text:0804A24A Sure_Enter: ; NOP .text:0804A24A lea esi, [esi] .text:0804A24C .text:0804A24C Backup_OutBuf_to_LocalBuf: ; CODE XREF: Decoder+73j .text:0804A24C mov esi, [ebp+PlainText] .text:0804A24F mov al, [edx+esi] .text:0804A252 mov esi, [ebp+tmpBuf_Decoder] .text:0804A255 mov [edx+esi], al ; [pLocalBuf] = [pOutBuf] .text:0804A255 ; for PacketSize .text:0804A258 inc edx ; Increment by 1 .text:0804A259 cmp edx, edi ; Compare Two Operands .text:0804A25B jl short Backup_OutBuf_to_LocalBuf ; Jump if Less (SF!=OF) .text:0804A25B .text:0804A25D .text:0804A25D Decoder_Bytes: ; CODE XREF: Decoder+60j .text:0804A25D mov esi, [ebp+PlainText] ; Pn = Cn - Cn-1 - 0x17 .text:0804A260 mov [esi], cl ; CL = (Last Byte - 2nd-last Byte .text:0804A260 ; - 0x17 + 0x200) % 0x100 .text:0804A262 mov edx, 1 .text:0804A267 cmp edx, edi ; Compare Two Operands .text:0804A269 jge short Assign_PlainText_to_OutBuf ; Jump if Greater or Equal (SF=OF) .text:0804A269 .text:0804A26B .text:0804A26B Sure_Enter_2: ; No Operation .text:0804A26B nop .text:0804A26C .text:0804A26C Restore_LocalBuf_to_OutBuf_1: ; CODE XREF: Decoder+94j .text:0804A26C mov esi, [ebp+tmpBuf_Decoder] .text:0804A26F mov al, [edx+esi-1] ; EDX indexes pLocalBuf .text:0804A26F ; starts at pLocalBuf, then .text:0804A26F ; pLocalBuf+1, pLocalBuf+2,... .text:0804A273 mov esi, [ebp+PlainText] .text:0804A276 mov [edx+esi], al ; [OutputBuf]=[pLocalBuf-1] .text:0804A279 inc edx ; Increment by 1 .text:0804A27A cmp edx, edi ; Compare Two Operands .text:0804A27C jl short Restore_LocalBuf_to_OutBuf_1 ; Jump if Less (SF!=OF) .text:0804A27C .text:0804A27E .text:0804A27E Assign_PlainText_to_OutBuf: ; CODE XREF: Decoder+81j .text:0804A27E mov esi, [ebp+tmpBuf_Decoder] .text:0804A281 push esi .text:0804A282 push ecx .text:0804A283 push offset aCS ; "%c%s" .text:0804A288 mov esi, [ebp+PlainText] .text:0804A28B push esi .text:0804A28C call sprintf ; Call Procedure .text:0804A28C .text:0804A291 add esp, 10h ; Add .text:0804A294 dec ebx ; Decrement by 1 .text:0804A295 jns Processing_1 ; EBX = n .text:0804A295 ; EDX = n-1 .text:0804A295 .text:0804A29B .text:0804A29B Exit_Decoder: ; CODE XREF: Decoder+26j .text:0804A29B lea esp, [ebp-10h] ; Load Effective Address .text:0804A29E pop ebx .text:0804A29F pop esi .text:0804A2A0 pop edi .text:0804A2A1 mov esp, ebp .text:0804A2A3 pop ebp .text:0804A2A4 retn ; Return Near from Procedure .text:0804A2A4 .text:0804A2A4 Decoder endp