对照加密解密(第二版/第三版)，分析CRC32如下：
PS：第二版CRC32计算算法有误，第三版已更正。看看FI的校验吧
seg014:04AB FileCRC proc far
seg014:04AB
seg014:04AB crc32tbl = byte ptr -58Eh
seg014:04AB offset_lo = word ptr -18Eh
seg014:04AB offset_hi = word ptr -18Ch
seg014:04AB dwCRC = dword ptr -18Ah
seg014:04AB var_185 = byte ptr -185h
seg014:04AB handle = byte ptr -184h
seg014:04AB filename = byte ptr -104h
seg014:04AB crc32lo = word ptr -4
seg014:04AB crc32hi = word ptr -2
seg014:04AB FileName = dword ptr 6
seg014:04AB crcvalue = dword ptr 0Ah
seg014:04AB arg_8 = word ptr 0Eh
seg014:04AB arg_A = word ptr 10h
seg014:04AB size_lo = word ptr 12h
seg014:04AB size_hi = word ptr 14h
seg014:04AB
seg014:04AB enter 58Eh, 0
seg014:04AF mov bx, ss
seg014:04B1 mov es, bx
seg014:04B3 mov bx, ds
seg014:04B5 cld
seg014:04B6 lea di, [bp+filename]
seg014:04BA lds si, [bp+FileName]
seg014:04BD lodsb
seg014:04BE stosb
seg014:04BF xchg ax, cx
seg014:04C0 xor ch, ch
seg014:04C2 rep movsb
seg014:04C4 mov ds, bx ；以下是利用CRC32多项式的值
seg014:04C6 mov edx, [bp+crcvalue] ；crcvalue=EDB88320
seg014:04CA lea di, [bp+crc32tbl] ；生成CRC32表
seg014:04CE xor bx, bx
seg014:04D0
seg014:04D0 for0:
seg014:04D0 xor eax, eax
seg014:04D3 mov al, bl
seg014:04D5 mov cx, 8
seg014:04D8
seg014:04D8 for1:
seg014:04D8 test al, 1
seg014:04DA pushf
seg014:04DB shr eax, 1
seg014:04DE popf
seg014:04DF jz short loc_6DB14
seg014:04E1 xor eax, edx
seg014:04E4
seg014:04E4 loc_6DB14:
seg014:04E4 loop for1
seg014:04E6 shl bx, 2
seg014:04E9 mov ss:[bx+di], eax
seg014:04ED shr bx, 2
seg014:04F0 inc bx
seg014:04F1 cmp bx, 255
seg014:04F5 jbe short for0 ； fill crc table
seg014:04F7 mov word ptr [bp+dwCRC], 0FFFFh ；CRC32初始值
seg014:04FD mov word ptr [bp+dwCRC+2], 0FFFFh
seg014:0503 cmp ds:BaseMem, 0
seg014:0508 jnz short open_checkcrc
seg014:050A jmp exit
seg014:050D
seg014:050D open_checkcrc:
seg014:050D lea di, [bp+handle]
seg014:0511 push ss
seg014:0512 push di
seg014:0513 push 'R'
seg014:0515 lea di, [bp+filename]
seg014:0519 push ss
seg014:051A push di
seg014:051B push cs
seg014:051C call near ptr OpenFile
seg014:051F or al, al
seg014:0521 jnz short checkcrc
seg014:0523 jmp exit
seg014:0526
seg014:0526 checkcrc:
seg014:0526 mov ax, [bp+size_lo]
seg014:0529 mov dx, [bp+size_hi]
seg014:052C cmp dx, ds:filesize_hi
seg014:0530 jg short loc_6DB6A
seg014:0532 jl short loc_6DB76
seg014:0534 cmp ax, ds:filesize_lo
seg014:0538 jbe short loc_6DB76
seg014:053A
seg014:053A loc_6DB6A:
seg014:053A xor ax, ax
seg014:053C mov [bp+offset_lo], ax
seg014:0540 mov [bp+offset_hi], ax
seg014:0544 jmp short loc_6DB84
seg014:0546
seg014:0546 loc_6DB76:
seg014:0546 mov ax, [bp+size_lo]
seg014:0549 mov dx, [bp+size_hi]
seg014:054C mov [bp+offset_lo], ax
seg014:0550 mov [bp+offset_hi], dx
seg014:0554
seg014:0554 loc_6DB84:
seg014:0554 mov ax, [bp+arg_8]
seg014:0557 mov dx, [bp+arg_A]
seg014:055A cmp dx, ds:filesize_hi
seg014:055E jg short loc_6DB98
seg014:0560 jl short loc_6DBA5
seg014:0562 cmp ax, ds:filesize_lo
seg014:0566 jbe short loc_6DBA5
seg014:0568
seg014:0568 loc_6DB98:
seg014:0568 mov ax, ds:filesize_lo
seg014:056B mov dx, ds:filesize_hi
seg014:056F mov [bp+arg_8], ax
seg014:0572 mov [bp+arg_A], dx
seg014:0575
seg014:0575 loc_6DBA5:
seg014:0575 lea di, [bp+handle]
seg014:0579 push ss
seg014:057A push di ; handle
seg014:057B push [bp+offset_hi] ; offset_hi
seg014:057F push [bp+offset_lo] ; offset_lo
seg014:0583 push cs
seg014:0584 call near ptr lseek_begin
seg014:0587 mov [bp+var_185], 0
seg014:058C
seg014:058C loc_6DBBC:
seg014:058C mov ax, [bp+arg_8]
seg014:058F mov dx, [bp+arg_A]
seg014:0592 sub ax, [bp+offset_lo]
seg014:0596 sbb dx, [bp+offset_hi]
seg014:059A cmp dx, 0
seg014:059D jg short loc_6DBD6
seg014:059F jl short loc_6DBDE
seg014:05A1 cmp ax, 0FFEFh
seg014:05A4 jbe short loc_6DBDE
seg014:05A6
seg014:05A6 loc_6DBD6:
seg014:05A6 mov ds:CRC_Len, 0FFEFh
seg014:05AC jmp short loc_6DBEF
seg014:05AE
seg014:05AE loc_6DBDE:
seg014:05AE mov ax, [bp+arg_8]
seg014:05B1 mov dx, [bp+arg_A]
seg014:05B4 sub ax, [bp+offset_lo]
seg014:05B8 sbb dx, [bp+offset_hi]
seg014:05BC mov ds:CRC_Len, ax
seg014:05BF
seg014:05BF loc_6DBEF:
seg014:05BF mov ax, ds:CRC_Len
seg014:05C2 xor dx, dx
seg014:05C4 add [bp+offset_lo], ax
seg014:05C8 adc [bp+offset_hi], dx
seg014:05CC lea di, [bp+handle]
seg014:05D0 push ss
seg014:05D1 push di ; handle
seg014:05D2 mov ax, ds:BaseMem
seg014:05D5 push ax
seg014:05D6 mov di, 1
seg014:05D9 pop es
seg014:05DA push es
seg014:05DB push di ; buffer
seg014:05DC push ds:CRC_Len ; bytes
seg014:05E0 push cs
seg014:05E1 call near ptr ReadFile
seg014:05E4 mov ds:CRC_Len, ax
seg014:05E7 mov dx, ds:CRC_Len
seg014:05EB or dx, dx
seg014:05ED jz short crcend
seg014:05EF lea si, [bp+crc32tbl] ；开始计算CRC32值
seg014:05F3 push ds:BaseMem
seg014:05F7 pop es
seg014:05F8 mov di, 1
seg014:05FB
seg014:05FB nextcrc:
seg014:05FB mov ebx, [bp+dwCRC]
seg014:0600 mov ecx, ebx
seg014:0603 shr ecx, 8
seg014:0607 xor bl, es:[di]
seg014:060A xor bh, bh
seg014:060C shl bx, 2
seg014:060F mov eax, ss:[bx+si]
seg014:0613 xor eax, ecx
seg014:0616 mov [bp+dwCRC], eax
seg014:061B inc di
seg014:061C cmp di, dx
seg014:061E jbe short nextcrc
seg014:0620
seg014:0620 crcend:
seg014:0620 call GetCh ；计算完毕
seg014:0623 or al, al
seg014:0625 jz short loc_6DC66
seg014:0627 xor ax, ax
seg014:0629 mov word ptr [bp+dwCRC], ax
seg014:062D mov word ptr [bp+dwCRC+2], ax
seg014:0631 mov [bp+var_185], 1
seg014:0636
seg014:0636 loc_6DC66:
seg014:0636 mov ax, [bp+offset_lo]
seg014:063A mov dx, [bp+offset_hi]
seg014:063E cmp dx, [bp+arg_A]
seg014:0641 jg short close_exit
seg014:0643 jl short loc_6DC7A
seg014:0645 cmp ax, [bp+arg_8]
seg014:0648 jnb short close_exit
seg014:064A
seg014:064A loc_6DC7A:
seg014:064A cmp [bp+var_185], 0
seg014:064F jnz short close_exit
seg014:0651 jmp loc_6DBBC
seg014:0654
seg014:0654 close_exit:
seg014:0654 lea di, [bp+handle]
seg014:0658 push ss
seg014:0659 push di ; handle
seg014:065A push cs
seg014:065B call near ptr CloseFile
seg014:065E
seg014:065E exit:
seg014:065E mov ax, word ptr [bp+dwCRC]
seg014:0662 mov dx, word ptr [bp+dwCRC+2]
seg014:0666 xor ax, 0FFFFh
seg014:0669 xor dx, 0FFFFh ; real CRC
seg014:066D mov [bp+crc32lo], ax
seg014:0670 mov [bp+crc32hi], dx
seg014:0673 mov ax, [bp+crc32lo]
seg014:0676 mov dx, [bp+crc32hi]
seg014:0679 leave
seg014:067A retf 10h
seg014:067A FileCRC endp
从上面可以看出CRC32校验不难找，但是，上面的其它校验还挺麻烦。
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