| Build the Decrypt |
decryptor script:
import struct
import hashlib
import hmac
import sys
# Standard AES S-box
AES_SBOX = bytes([
0x63, 0x7C, 0x77, 0x7B, 0xF2, 0x6B, 0x6F, 0xC5, 0x30, 0x01, 0x67, 0x2B, 0xFE, 0xD7, 0xAB, 0x76,
0xCA, 0x82, 0xC9, 0x7D, 0xFA, 0x59, 0x47, 0xF0, 0xAD, 0xD4, 0xA2, 0xAF, 0x9C, 0xA4, 0x72, 0xC0,
0xB7, 0xFD, 0x93, 0x26, 0x36, 0x3F, 0xF7, 0xCC, 0x34, 0xA5, 0xE5, 0xF1, 0x71, 0xD8, 0x31, 0x15,
0x04, 0xC7, 0x23, 0xC3, 0x18, 0x96, 0x05, 0x9A, 0x07, 0x12, 0x80, 0xE2, 0xEB, 0x27, 0xB2, 0x75,
0x09, 0x83, 0x2C, 0x1A, 0x1B, 0x6E, 0x5A, 0xA0, 0x52, 0x3B, 0xD6, 0xB3, 0x29, 0xE3, 0x2F, 0x84,
0x53, 0xD1, 0x00, 0xED, 0x20, 0xFC, 0xB1, 0x5B, 0x6A, 0xCB, 0xBE, 0x39, 0x4A, 0x4C, 0x58, 0xCF,
0xD0, 0xEF, 0xAA, 0xFB, 0x43, 0x4D, 0x33, 0x85, 0x45, 0xF9, 0x02, 0x7F, 0x50, 0x3C, 0x9F, 0xA8,
0x51, 0xA3, 0x40, 0x8F, 0x92, 0x9D, 0x38, 0xF5, 0xBC, 0xB6, 0xDA, 0x21, 0x10, 0xFF, 0xF3, 0xD2,
0xCD, 0x0C, 0x13, 0xEC, 0x5F, 0x97, 0x44, 0x17, 0xC4, 0xA7, 0x7E, 0x3D, 0x64, 0x5D, 0x19, 0x73,
0x60, 0x81, 0x4F, 0xDC, 0x22, 0x2A, 0x90, 0x88, 0x46, 0xEE, 0xB8, 0x14, 0xDE, 0x5E, 0x0B, 0xDB,
0xE0, 0x32, 0x3A, 0x0A, 0x49, 0x06, 0x24, 0x5C, 0xC2, 0xD3, 0xAC, 0x62, 0x91, 0x95, 0xE4, 0x79,
0xE7, 0xC8, 0x37, 0x6D, 0x8D, 0xD5, 0x4E, 0xA9, 0x6C, 0x56, 0xF4, 0xEA, 0x65, 0x7A, 0xAE, 0x08,
0xBA, 0x78, 0x25, 0x2E, 0x1C, 0xA6, 0xB4, 0xC6, 0xE8, 0xDD, 0x74, 0x1F, 0x4B, 0xBD, 0x8B, 0x8A,
0x70, 0x3E, 0xB5, 0x66, 0x48, 0x03, 0xF6, 0x0E, 0x61, 0x35, 0x57, 0xB9, 0x86, 0xC1, 0x1D, 0x9E,
0xE1, 0xF8, 0x98, 0x11, 0x69, 0xD9, 0x8E, 0x94, 0x9B, 0x1E, 0x87, 0xE9, 0xCE, 0x55, 0x28, 0xDF,
0x8C, 0xA1, 0x89, 0x0D, 0xBF, 0xE6, 0x42, 0x68, 0x41, 0x99, 0x2D, 0x0F, 0xB0, 0x54, 0xBB, 0x16
])
def rol64(val, bits):
val &= 0xFFFFFFFFFFFFFFFF
return ((val << bits) | (val >> (64 - bits))) & 0xFFFFFFFFFFFFFFFF
def ror64(val, bits):
val &= 0xFFFFFFFFFFFFFFFF
return ((val >> bits) | (val << (64 - bits))) & 0xFFFFFFFFFFFFFFFF
def derive_keys(password, iv):
# HKDF-ish key derivation
pwd_wstr = password.encode('utf-16le') # wstring encoding
pwd_hash = hashlib.sha256(pwd_wstr).digest()
master_key = hmac.new(iv, pwd_hash, hashlib.sha256).digest()
enc_key = hmac.new(master_key, b'enc', hashlib.sha256).digest()
mac_key = hmac.new(master_key, b'mac', hashlib.sha256).digest()
return enc_key, mac_key
def rc4_ksa(s_box, key):
# RC4 key scheduling but starting from AES S-box instead of [0..255]
# This was the main trick!
S = list(s_box)
j = 0
for i in range(256):
j = (j + S[i] + key[i & 0x1F]) & 0xFF
S[i], S[j] = S[j], S[i]
return bytes(S)
def reverse_substitution_layer(ciphertext, S, key):
result = bytearray(ciphertext)
n = len(result)
if n == 0:
return bytes(result)
# Build inverse S-box
inv_S = bytearray(256)
for i in range(256):
inv_S[S[i]] = i
# Decrypt with state tracking
v42 = key[0]
v43 = key[31]
for j in range(n):
v45 = key[j & 0x1F]
encrypted_byte = result[j]
# Reverse the substitution formula
plaintext_byte = inv_S[(encrypted_byte - v43) & 0xFF] ^ v42
result[j] = plaintext_byte
# Update states for next iteration
v42 = v45 ^ plaintext_byte
v43 = encrypted_byte ^ v45
return bytes(result)
def reverse_chacha_stream(ciphertext, enc_key):
# XOR-based stream cipher with ChaCha-inspired mixing
result = bytearray(ciphertext)
n = len(result)
if n == 0:
return bytes(result)
# Initialize state from key
v34 = struct.unpack('<Q', enc_key[0:8])[0] ^ 0x6A09E667F3BCC908
v35 = struct.unpack('<Q', enc_key[8:16])[0] ^ 0xBB67AE8584CAA73B
v36 = struct.unpack('<Q', enc_key[16:24])[0] ^ 0x3C6EF372FE94F82B
v37 = struct.unpack('<Q', enc_key[24:32])[0] ^ 0xA54FF53A5F1D36F1
S = rc4_ksa(AES_SBOX, enc_key)
v68 = 0
for pos in range(n):
if (pos & 7) == 0:
# Full round every 8 bytes
v38 = (v35 + v34) & 0xFFFFFFFFFFFFFFFF
v37 = rol64(v38 ^ v37, 23)
v36 = (v36 + v37) & 0xFFFFFFFFFFFFFFFF
v39 = (v38 ^ S[v38 & 0xFF]) & 0xFFFFFFFFFFFFFFFF
v35 = ror64(v36 ^ v35, 23)
v68 = (v37 ^ v36 ^ v39 ^ v35) & 0xFFFFFFFFFFFFFFFF
keystream_byte = v68 & 0xFF
plaintext_byte = result[pos] ^ keystream_byte
result[pos] = plaintext_byte
v34 = (v39 + plaintext_byte) & 0xFFFFFFFFFFFFFFFF
else:
# Reuse keystream for next 7 bytes
v68 = (v37 ^ v36 ^ v34 ^ v35) & 0xFFFFFFFFFFFFFFFF
keystream_byte = (v68 >> ((pos & 7) * 8)) & 0xFF
ciphertext_byte = result[pos]
plaintext_byte = ciphertext_byte ^ keystream_byte
result[pos] = plaintext_byte
v34 = (v34 + plaintext_byte) & 0xFFFFFFFFFFFFFFFF
return bytes(result)
def decrypt_file(filepath, password):
with open(filepath, 'rb') as f:
data = f.read()
# Parse file format
magic = data[0:3]
version = struct.unpack('<H', data[3:5])[0]
iv = data[5:21]
ciphertext = data[21:-32]
stored_mac = data[-32:]
print(f"[*] File: {magic}, version {version}")
print(f"[*] IV: {iv.hex()}")
print(f"[*] Ciphertext: {len(ciphertext)} bytes")
# Derive keys from password
enc_key, mac_key = derive_keys(password, iv)
# Verify integrity
computed_mac = hmac.new(mac_key, ciphertext, hashlib.sha256).digest()
if computed_mac != stored_mac:
print("[!] MAC verification failed!")
return None
print("[+] MAC verified")
# Decrypt: reverse substitution, then reverse stream cipher
S = rc4_ksa(AES_SBOX, enc_key)
temp = reverse_substitution_layer(ciphertext, S, enc_key)
plaintext = reverse_chacha_stream(temp, enc_key)
print(f"\n[+] Decrypted: {plaintext.decode('utf-8')}")
return plaintext
if __name__ == "__main__":
filepath = sys.argv[1] if len(sys.argv) > 1 else "decryptme.txt"
password = "123"
print(f"Decrypting {filepath}...\n")
decrypt_file(filepath, password)
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2026-02-14 12:01 |