[MASM] RC4 Encryption

[Gonzalez]

.386p
.model flat, stdcall
option casemap:none  ; Case sensitive
include  \Masm32\include\windows.inc
include  \Masm32\include\kernel32.inc
include  \Masm32\include\user32.inc
includelib  \Masm32\lib\kernel32.lib
includelib  \Masm32\lib\user32.lib
EnDeCryptfile proto :DWORD
EnDeCryptfile2 proto :DWORD,:DWORD
Rc4_setkey proto :DWORD,:DWORD
Rc4_crypt proto :DWORD, :DWORD

     CTEXT MACRO text:VARARG
            LOCAL TxtName
              .data
               TxtName BYTE text,0
              .code
            EXITM <ADDR TxtName>
     ENDM

.data
mykey db "omgwtfjusthappenedtherethen",0


.data?
data db 1024 dup(?)        ; bytes read/write, can be turned up
rc4keytable db 256 dup (?)
HoldBuf db 256 dup(?)
hFileRead dd ?
SizeWritten dd ?
SizeWritten2 dd ?
hFileRead2 dd ?

.code
start:


invoke EnDeCryptfile,CTEXT("RC4d.exe") ; encrypts RC4.exe
;invoke EnDeCryptfile,CTEXT("RC4d.exe"); decrypt RC4.exe

;file test 2
invoke EnDeCryptfile2,CTEXT("original.exe"),CTEXT("ENCRYPTED")
invoke EnDeCryptfile2,CTEXT("ENCRYPTED"),CTEXT("DENCRYPTED.exe")




invoke ExitProcess,0

;writes encrypted/decrypted data back into same file
EnDeCryptfile proc inputfile:DWORD
invoke CreateFile,inputfile,GENERIC_READ or GENERIC_WRITE,FILE_SHARE_READ or FILE_SHARE_WRITE,NULL,OPEN_EXISTING,FILE_ATTRIBUTE_ARCHIVE,NULL
cmp eax,INVALID_HANDLE_VALUE
je @F
mov hFileRead,eax
.while TRUE
    invoke ReadFile,hFileRead,addr data,1,ADDR SizeWritten,NULL
.break .if eax && SizeWritten == 0
    invoke lstrlen,addr mykey
    invoke Rc4_setkey,addr mykey,eax
    invoke Rc4_crypt,addr data,1
    invoke SetFilePointer,hFileRead,-1,0,FILE_CURRENT
    invoke WriteFile,hFileRead,addr data,1,ADDR SizeWritten2,NULL
.endw
invoke CloseHandle,hFileRead   
@@:
ret
EnDeCryptfile endp


;writes en/decrypted file to external file, reads and writes 1024 bytes at a time but you can read as many as you like if you change the buffer size
EnDeCryptfile2 proc inputfile:DWORD,savepath:DWORD
invoke CreateFile,inputfile,GENERIC_READ or GENERIC_WRITE,FILE_SHARE_READ or FILE_SHARE_WRITE,NULL,OPEN_EXISTING,FILE_ATTRIBUTE_ARCHIVE,NULL
cmp eax,INVALID_HANDLE_VALUE
je @F
mov hFileRead,eax
invoke CreateFile,savepath,GENERIC_READ or GENERIC_WRITE,FILE_SHARE_READ or FILE_SHARE_WRITE,NULL,CREATE_ALWAYS,FILE_ATTRIBUTE_ARCHIVE,NULL
mov hFileRead2,eax
.while TRUE
    invoke ReadFile,hFileRead,addr data,1024,ADDR SizeWritten,NULL
.break .if eax && SizeWritten == 0
    invoke lstrlen,addr mykey
    invoke Rc4_setkey,addr mykey,eax
    invoke Rc4_crypt,addr data,1024
    invoke WriteFile,hFileRead2,addr data,1024,ADDR SizeWritten2,NULL
.endw
invoke CloseHandle,hFileRead
invoke CloseHandle,hFileRead2   
@@:
ret
EnDeCryptfile2 endp





Rc4_setkey proc Pass:DWORD, LenPass:DWORD
pushad

mov eax, 0FFFEFDFCh
mov ecx, 256/4
Init_rc4keytable:
mov dword ptr [rc4keytable+4*ecx-4], eax
sub eax, 04040404h
dec ecx
jnz Init_rc4keytable

xor eax, eax
mov edi, Pass

Key_return:
xor ebx, ebx
mov esi ,LenPass
jmp New_key

Key_loop:
inc bl
dec esi
jz Key_return

New_key:
mov dl, byte ptr [rc4keytable+ecx]
add al, byte ptr [edi+ebx]
add al, dl
mov dh, byte ptr [rc4keytable+eax]
mov byte ptr [rc4keytable+ecx], dh
mov byte ptr [rc4keytable+eax], dl
inc cl
jnz Key_loop

popad
ret
Rc4_setkey endp

Rc4_crypt proc iData:DWORD, LenData:DWORD
pushad
mov edi, LenData
mov esi, iData
test edi, edi
jz Rc4_enc_exit

xor eax, eax
xor edx, edx
xor ecx, ecx
        xor ebx, ebx

Rc4_enc_loop:
inc bl
mov dl, byte ptr [rc4keytable+ebx]
add al, dl
mov cl, byte ptr [rc4keytable+eax]
mov byte ptr [rc4keytable+ebx], cl
mov byte ptr [rc4keytable+eax], dl
add cl, dl
mov cl, byte ptr [rc4keytable+ecx]
xor byte ptr [esi], cl
inc esi
dec edi
jnz Rc4_enc_loop

xor eax, eax
mov edi, offset rc4keytable
mov ecx, 256/4
cld
rep stosd

Rc4_enc_exit:
popad
ret
Rc4_crypt endp

end start

eNj0Y!