You are given an assembly program that generates a CRC-32 lookup table and then computes a CRC-32–style hash over four input bytes. The task is to: Understand how the table is generated Follow the hash routine step-by-step (XOR with CRC low byte, lookup, shift, XOR) Reproduce the same logic in your own code Compute the final 32-bit value returned in EAX ==================================================== ; ========= CONFIG ========= ; SASM: Mode = NASM, 64-bit section .data input_data db 0x4B,0x43,0x43,0x48 input_len dq 4 section .bss lut resd 256 section .text global _start ; ========= ENTRY ========= _start: call hash ; print result (in hex) just to verify mov rdi, rax ; exit mov rax, 60 xor rdi, rdi syscall ; ========= CRC TABLE GENERATOR ========= generate_table: xor rcx, rcx ; i = 0 .gen_outer: cmp rcx, 256 je .done_outer mov eax, ecx ; t = i mov rdx, 0 ; j = 0 .gen_inner: cmp rdx, 8 je .store test al, 1 jz .no_xor shr eax, 1 xor eax, 0xEDB88320 jmp .next .no_xor: shr eax, 1 .next: inc rdx jmp .gen_inner .store: mov dword [lut + rcx*4], eax inc rcx jmp .gen_outer .done_outer: ret ; ========= CRC HASH FUNCTION ========= hash: call generate_table mov rbx, input_data mov rcx, [input_len] mov eax, 0xffffffff ; CRC xor rdx, rdx ; index = 0 .loop: cmp rdx, rcx je .done mov bl, [input_data + rdx] ; read byte xor bl, al ; CRC low byte ^ input movzx r8d, bl ; r8d = index (0..255) shr eax, 8 xor eax, dword [lut + r8d*4] inc rdx jmp .loop .done: xor eax, 0xffffffff ret =================================================================== My pyhton program def generate_table(): lut = [0] * 256 for i in range(256): t = i for _ in range(8): if t & 1: t = (t >> 1) ^ 0xEDB88320 else: t = t >> 1 lut = t & 0xFFFFFFFF return lut def crc32_exact_asm(data_bytes): lut = generate_table() crc = 0xFFFFFFFF index = 0 length = len(data_bytes) while index < length: input_byte = data_bytes[index] & 0xFF index_val = (input_byte ^ (crc & 0xFF)) & 0xFF crc = (crc >> 8) & 0xFFFFFFFF crc = (crc ^ lut[index_val]) & 0xFFFFFFFF index += 1 crc = crc ^ 0xFFFFFFFF return crc & 0xFFFFFFFF data = [0x4B, 0x43, 0x43, 0x48] result = crc32_exact_asm(data) print(hex(result)) Continue reading...