Re: LZ: Self Encrypting Programs
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Re: LZ: Self Encrypting Programs
Michael Wyman wrote:
>
> I had a thought a while ago, about making a program self encrypting (and
> decrypting) so that while the program is running, the code is decrypted and
> in the actual opcodes. When the program exits, it encrypts itself, thereby
> making it virtually impossible to decompile unless somebody has a lot of
> time on their hands, as well as hiding the location of variables
> (passwords and such). Tell me what you think!
>
> #include ti-85.h
>
> *org 0
> db "(whatever)", 0
> ;start of decryption
> ld hl, Encrypt_loop
> ld de, Encrypted_byte
> sbc hl, de
> ex de, hl
> push de
> ld bc, (PROGRAM_ADDR)
> add hl, bc
> push hl
> ld a, (hl)
> cp $0f
> jr Z, Prog_Start
> Decrypt_loop:
> ld a, (hl)
> xor $ff
> ld (hl), a
> inc hl
> dec de
> jr nz, Decrypt_loop
> jr Prog_Start
> Encypted_byte:
> db $0f
> Prog_Start:
If you have it rewrite itself at the begining it should loose the revert
to original when it exits lots of computer programs did this to prevent
people from modifying them.
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