Keep's sygil.fun

Author:
Keep

Language:
C/C++

Upload:
2026-09-16 00:54

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Platform:
Unix/linux etc.

Difficulty:
3.5

Quality:
4.0

Arch:
x86-64

Downloads:
59

Size:
14.22 KB

Writeups:
1

Comments:
2

Description

a ritualistic keygenme. you must weave a valid sigil to bind your name to the pact. rules for the ritual: * you must write a working keygen. * no patching the binary (the spirits will know). * your name must be at least 4 characters long. * all outputs are strictly lowercase. good luck. first crackme,, made with <3 by lovemf --to whoever is reviewing this, i am new and not sure how i can prove that its solvable by me but i have a working keygen script. dont know if i should upload it here or what haha

Labels ?

Anti-debugging ptrace (Linux) String / data encryption XOR Crypto / hash algorithm Other / custom hash

Comments (2)
Writeups (1)

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Keep on 2026-09-16 14:49: i would like to add be on the lookout for a ui version, i was gonna work on it for like another month but im not having fun with it anymore :(

SVz on 2026-09-16 16:17: [Click to reveal]#!/usr/bin/env python3 """ Computes the "sigil" expected by the sygil crackme for a given name. Algorithm extracted from sub_401690 (Binary Ninja): hash = 0x811C9DC5 # FNV-1a offset basis for each byte c of `name` (until '\n' or end of string): hash = ((hash ^ c) * 0x01000193) & 0xFFFFFFFF # FNV-1a prime if the process is traced (ptrace detected via /proc/self/status): hash ^= 0xDEADBEEF a = hash ^ 0x5947494C b = (hash >> 16) ^ (hash & 0xFFFF) # movzx edx, dx before the xor: 16-bit fold c = a ^ b ^ 0x535947 sigil = f"syg-{a:08x}-{b:04x}-{c:08x}" Detail confirmed from the disassembly (not just the pseudo-C): - `movsx eax, byte [rdi]`: each byte of name is read SIGNED (sign-extend), not zero-extended, before the xor/imul. - `movzx edx, dx` right before `xor ecx, edx`: b is actually a XOR between the high word and the low word of hash, not (hash>>16) ^ hash over 32 bits. """ import argparse FNV_OFFSET = 0x811C9DC5 FNV_PRIME = 0x01000193 MASK32 = 0xFFFFFFFF def _signed_byte_as_32(c: int) -> int: """Reproduces movsx eax, byte[rdi]: sign-extends byte c to 32 bits.""" if c < 0x80: return c return 0xFFFFFF00 | c def sygil_hash(name: str, traced: bool = False) -> int: h = FNV_OFFSET for c in name.encode(): if c == 0x0A: # '\n' break h = ((h ^ _signed_byte_as_32(c)) * FNV_PRIME) & MASK32 if traced: h ^= 0xDEADBEEF return h & MASK32 def compute_sigil(name: str, traced: bool = False) -> str: h = sygil_hash(name, traced) a = (h ^ 0x5947494C) & MASK32 b = ((h >> 16) ^ (h & 0xFFFF)) & MASK32 c = (a ^ b ^ 0x535947) & MASK32 return f"syg-{a:08x}-{b:04x}-{c:08x}" def main(): parser = argparse.ArgumentParser(description="Computes the expected sigil for a given name (sygil crackme)") parser.add_argument("name", help="value to enter at the 'name: ' prompt") parser.add_argument("--traced", action="store_true", help="simulate the case where the binary detects a tracer (anti-debug active)") args = parser.parse_args() if len(args.name) <= 3: parser.error("the binary requires strlen(name) > 3") sigil = compute_sigil(args.name, traced=args.traced) print(f"name : {args.name}") print(f"sigil: {sigil}") if __name__ == "__main__": main()

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Solution by vetementsvmnts on 2026-09-16 17:28:
Python keygen based on FNV-1a hash of the name.

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Keep's sygil.fun