"description": "No\udb40\udd27\udb40\udd28\udb40...

python
import json, re, textwrap, sys, unicodedata, binascii, base64
s = r'''"description": "No\udb40\udd27\udb40\udd28\udb40\udd55\udb40\udd54\udb40\udd22\udb40\udd28 f\udb40\udd29\udb40\udd53\udb40\udd55\udb40\udd22\udb40\udd25\udb40\udd55i\udb40\udd20\udb40\udd25\udb40\udd55\udb40\udd20\udb40\udd23\udb40\udd56l\udb40\udd24\udb40\udd20\udb40\udd56\udb40\udd54\udb40\udd20\udb40\udd51e\udb40\udd23\udb40\udd52\udb40\udd53\udb40\udd23\udb40\udd54\udb40\udd27s\udb40\udd20\udb40\udd51\udb40\udd21\udb40\udd24\udb40\udd56\udb40\udd23 n\udb40\udd28\udb40\udd20\udb40\udd24\udb40\udd26\udb40\udd56\udb40\udd20e\udb40\udd23\udb40\udd20\udb40\udd52\udb40\udd26\udb40\udd22\udb40\udd24e\udb40\udd20\udb40\udd53\udb40\udd55\udb40\udd54\udb40\udd20\udb40\udd27d\udb40\udd23\udb40\udd54\udb40\udd25\udb40\udd55\udb40\udd23\udb40\udd54e\udb40\udd28\udb40\udd52\udb40\udd24\udb40\udd21\udb40\udd53\udb40\udd51d\udb40\udd23\udb40\udd28\udb40\udd23\udb40\udd28\udb40\udd20\udb40\udd54, h\udb40\udd56\udb40\udd28\udb40\udd52\udb40\udd25\udb40\udd27\udb40\udd51e\udb40\udd24\udb40\udd23\udb40\udd53\udb40\udd51r\udb40\udd27\udb40\udd20\udb40\udd26\udb40\udd51e\udb40\udd24\udb40\udd52\udb40\udd56\udb40\udd54 i\udb40\udd20\udb40\udd24\udb40\udd29\udb40\udd22s\udb40\udd21\udb40\udd21\udb40\udd27\udb40\udd24 y\udb40\udd56\udb40\udd22\udb40\udd51\udb40\udd27o\udb40\udd20\udb40\udd28\udb40\udd51\udb40\udd23u\udb40\udd28\udb40\udd22\udb40\udd24\udb40\udd25r\udb40\udd25\udb40\udd29\udb40\udd55\udb40\udd55 f\udb40\udd29\udb40\udd24\udb40\udd29\udb40\udd51l\udb40\udd55\udb40\udd55\udb40\udd22\udb40\udd22a\udb40\udd25\udb40\udd25\udb40\udd24\udb40\udd21g\udb40\udd53\udb40\udd24\udb40\udd52\udb40\udd55\ud83d\udc40\udb40\udd51\udb40\udd54\udb40\udd25\udb40\udd27\ufe0a"'''
# Make it valid json object
j = '{' + s + '}'
obj = json.loads(j)
desc = obj["description"]
desc[:50], len(desc)


('No󠄧󠄨󠅕󠅔󠄢󠄨 f󠄩󠅓󠅕󠄢󠄥󠅕i󠄠󠄥󠅕󠄠󠄣󠅖l󠄤󠄠󠅖󠅔󠄠󠅑e󠄣󠅒󠅓󠄣󠅔󠄧s󠄠󠅑󠄡󠄤󠅖󠄣 n󠄨󠄠󠄤󠄦', 170)

python
vs = []
for ch in desc:
    cp = ord(ch)
    if 0xFE00 <= cp <= 0xFE0F or 0xE0100 <= cp <= 0xE01EF:
        vs.append(cp)
len(vs), vs[:10], hex(vs[0])


(135,
 [917799,
  917800,
  917845,
  917844,
  917794,
  917800,
  917801,
  917843,
  917845,
  917794],
 '0xe0127')

python
def vs_to_val(cp):
    if 0xFE00 <= cp <= 0xFE0F:
        return cp - 0xFE00
    if 0xE0100 <= cp <= 0xE01EF:
        return cp - 0xE0100 + 16
    raise ValueError
vals = [vs_to_val(cp) for cp in vs]
vals[:20], min(vals), max(vals), len(vals)


([55,
  56,
  101,
  100,
  50,
  56,
  57,
  99,
  101,
  50,
  53,
  101,
  48,
  53,
  101,
  48,
  51,
  102,
  52,
  48],
 10,
 102,
 135)

python
data = bytes(vals)
data[:50], data.decode('ascii', errors='replace')[:200]


(b'78ed289ce25e05e03f40fd0a3bc3d70a14f38046f030b6240c',
 '78ed289ce25e05e03f40fd0a3bc3d70a14f38046f030b6240ced073d5e3d8b41ca38380df8b57a43ca706a4bfd04921174f2a708a3824559ee949aee225541c4bead57\n')

python
txt = data.decode('ascii')
txt, len(txt)


('78ed289ce25e05e03f40fd0a3bc3d70a14f38046f030b6240ced073d5e3d8b41ca38380df8b57a43ca706a4bfd04921174f2a708a3824559ee949aee225541c4bead57\n',
 135)

python
hexstr = txt.strip()
len(hexstr), hexstr[:40], hexstr[-40:]


(134,
 '78ed289ce25e05e03f40fd0a3bc3d70a14f38046',
 '1174f2a708a3824559ee949aee225541c4bead57')

python
cipher = bytes.fromhex(hexstr)
len(cipher), cipher[:10], cipher[-10:]


(67, b'x\xed(\x9c\xe2^\x05\xe0?@', b'\x94\x9a\xee"UA\xc4\xbe\xadW')

python
30957 % 31


19

python
import string
print(cipher)
print(''.join(chr(b) if 32<=b<127 else '.' for b in cipher))

python
import pkgutil, sys
'cryptography' in [m.name for m in pkgutil.iter_modules()]


True

python
from cryptography.hazmat.primitives.ciphers.aead import XChaCha20Poly1305, ChaCha20Poly1305
from cryptography.hazmat.primitives import hashes
from cryptography.hazmat.backends import default_backend

def sha256(b):
    h=hashes.Hash(hashes.SHA256()); h.update(b); return h.finalize()

key = sha256(b"0xOsama")
nonce = cipher[:24]
ct = cipher[24:]
len(nonce), len(ct)

python
import pkgutil, sys
[n for n in ['nacl','pynacl','Crypto','Cryptodome','pycryptodome'] if any(m.name==n for m in pkgutil.iter_modules())][:10]


['nacl', 'Crypto']

python
from nacl.secret import SecretBox
from nacl.exceptions import CryptoError
import hashlib, itertools, base64, binascii, os, math, re, string
cipher = bytes.fromhex(hexstr)
nonce24 = cipher[:24]
ct_rest = cipher[24:]  # includes mac?
len(cipher), len(nonce24), len(ct_rest)


(67, 24, 43)

python
key = hashlib.sha256(b"0xOsama").digest()
box = SecretBox(key)
try:
    pt = box.decrypt(ct_rest, nonce24)
    print(pt, pt.decode())
except Exception as e:
    print("err", type(e), e)

python
import itertools, math, string, numpy as np, hashlib, re
cipher = bytes.fromhex(hexstr)

printable = set(bytes(string.printable, 'ascii'))
# but string.printable includes whitespace; allow some.
def score_plain(p):
    # high if mostly printable and contains flag markers
    pr = sum(b in printable for b in p)/len(p)
    # bonus for common substrings
    s = p.decode('latin1', errors='ignore')
    bonus = 0
    for token in ["flag{", "FLAG{", "ctf{", "CTF{", "{", "}"]:
        if token in s: bonus += 0.5
    # penalize control
    ctrl = sum(b<9 or (13<b<32) for b in p)/len(p)
    return pr - ctrl + bonus

def best_xor_key_for_len(klen):
    key = bytearray(klen)
    for i in range(klen):
        column = cipher[i::klen]
        best = None
        bestscore = -1e9
        for kb in range(256):
            p = bytes([b ^ kb for b in column])
            # score by printable ratio
            pr = sum((32<=x<127) or x in (9,10,13) for x in p)/len(p)
            if pr > bestscore:
                bestscore = pr; best = kb
        key[i]=best
    pt = bytes([b ^ key[i%klen] for i,b in enumerate(cipher)])
    return bytes(key), pt, score_plain(pt)

cands=[]
for klen in range(1,41):
    key, pt, sc = best_xor_key_for_len(klen)
    cands.append((sc,klen,key,pt))
cands_sorted = sorted(cands, reverse=True, key=lambda x:x[0])
cands_sorted[:10][0:3]


[(1.7313432835820897,
  31,
  b'\x00\x80\x00\x91\x00\x00\x08\x00\x00\x00\x00\x00\x00\x80\t\x00 \x00\x89\x00\x01\x00\x88\x00\x01\x80\n\x00\x00\x00\x00',
  b'xm(\r\xe2^\r\xe0?@\xfd\n;C\xde\n4\xf3\tF\xf10>$\rm\r=^=\x8bAJ8\xa9\r\xf8\xbdzC\xcapjK}\r\x921t{\xa7\t\xa3\nEXn\x9e\x9a\xee"UAD\xbe<W'),
 (1.716417910447761,
  13,
  b'\n\x88\x00\x19\x81\xa0 \x98\x18\x00\x80\x80\x01',
  b"re(\x85c\xfe%x'@}\x8a:\xc9_\n\rr fh(\xb6\xa4\x8c\xec\r\xb5^$\n\xe1\xea\xa0 \rx5{IBps\xca]$\n\ttr'\t\xa9\nE@o4\xbav:U\xc1D\xbf\xa7\xdf"),
 (1.626865671641791,
  8,
  b'2\x99\n0\x80\t\x08)',
  b'Jt"\xacbW\r\xc9\r\xd9\xf7:\xbb\xca\xdf#&j\x8avp9\xbe\r>t\r\r\xde4\x83h\xf8\xa12=x\xbcrj\xf8\xe9`{}\r\x9a8Fk\xad8#\x8bMp\xdc\r\x90\xde\xa2\\I\xed\x8c4]')]

python
rev = cipher[::-1]
print(rev[:10], rev[-10:])
print((rev[0]*256 + rev[1])%31)

python
# extract visible message by removing variation selectors and other hidden
visible = ''.join(ch for ch in desc if not (0xFE00<=ord(ch)<=0xFE0F or 0xE0100<=ord(ch)<=0xE01EF))
visible


'No files needed, here is your flag👀'

python
import json, re, hashlib, base64, binascii, textwrap, string, itertools, math
full_s = r'''"description": "No\udb40\udd27\udb40\udd28\udb40\udd55\udb40\udd54\udb40\udd22\udb40\udd28 f\udb40\udd29\udb40\udd53\udb40\udd55\udb40\udd22\udb40\udd25\udb40\udd55i\udb40\udd20\udb40\udd25\udb40\udd55\udb40\udd20\udb40\udd23\udb40\udd56l\udb40\udd24\udb40\udd20\udb40\udd56\udb40\udd54\udb40\udd20\udb40\udd51e\udb40\udd23\udb40\udd52\udb40\udd53\udb40\udd23\udb40\udd54\udb40\udd27s\udb40\udd20\udb40\udd51\udb40\udd21\udb40\udd24\udb40\udd56\udb40\udd23 n\udb40\udd28\udb40\udd20\udb40\udd24\udb40\udd26\udb40\udd56\udb40\udd20e\udb40\udd23\udb40\udd20\udb40\udd52\udb40\udd26\udb40\udd22\udb40\udd24e\udb40\udd20\udb40\udd53\udb40\udd55\udb40\udd54\udb40\udd20\udb40\udd27d\udb40\udd23\udb40\udd54\udb40\udd25\udb40\udd55\udb40\udd23\udb40\udd54e\udb40\udd28\udb40\udd52\udb40\udd24\udb40\udd21\udb40\udd53\udb40\udd51d\udb40\udd23\udb40\udd28\udb40\udd23\udb40\udd28\udb40\udd20\udb40\udd54, h\udb40\udd56\udb40\udd28\udb40\udd52\udb40\udd25\udb40\udd27\udb40\udd51e\udb40\udd24\udb40\udd23\udb40\udd53\udb40\udd51r\udb40\udd27\udb40\udd20\udb40\udd26\udb40\udd51e\udb40\udd24\udb40\udd52\udb40\udd56\udb40\udd54 i\udb40\udd20\udb40\udd24\udb40\udd29\udb40\udd22s\udb40\udd21\udb40\udd21\udb40\udd27\udb40\udd24 y\udb40\udd56\udb40\udd22\udb40\udd51\udb40\udd27o\udb40\udd20\udb40\udd28\udb40\udd51\udb40\udd23u\udb40\udd28\udb40\udd22\udb40\udd24\udb40\udd25r\udb40\udd25\udb40\udd29\udb40\udd55\udb40\udd55 f\udb40\udd29\udb40\udd24\udb40\udd29\udb40\udd51l\udb40\udd55\udb40\udd55\udb40\udd22\udb40\udd22a\udb40\udd25\udb40\udd25\udb40\udd24\udb40\udd21g\udb40\udd53\udb40\udd24\udb40\udd52\udb40\udd55\ud83d\udc40\udb40\udd51\udb40\udd54\udb40\udd25\udb40\udd27\ufe0a"'''
obj = json.loads('{' + full_s + '}')
desc_full = obj["description"]
len(desc_full), desc_full[:60], desc_full[-10:]


(170,
 'No󠄧󠄨󠅕󠅔󠄢󠄨 f󠄩󠅓󠅕󠄢󠄥󠅕i󠄠󠄥󠅕󠄠󠄣󠅖l󠄤󠄠󠅖󠅔󠄠󠅑e󠄣󠅒󠅓󠄣󠅔󠄧s󠄠󠅑󠄡󠄤󠅖󠄣 n󠄨󠄠󠄤󠄦󠅖󠄠e󠄣󠄠󠅒󠄦󠄢󠄤e',
 '󠅓󠄤󠅒󠅕👀󠅑󠅔󠄥󠄧︊')

python
import math
from collections import Counter
counts = Counter(cipher)
entropy = -sum((c/len(cipher))*math.log2(c/len(cipher)) for c in counts.values())
entropy


5.797432474039859

python
visible = ''.join(ch for ch in desc_full if not (0xFE00<=ord(ch)<=0xFE0F or 0xE0100<=ord(ch)<=0xE01EF))
visible


'No files needed, here is your flag👀'

python
def single_xor_best(cipher):
    best=None
    for k in range(256):
        pt=bytes([b^k for b in cipher])
        # compute printable ratio
        pr=sum(32<=x<127 or x in (10,13,9) for x in pt)/len(pt)
        if best is None or pr>best[0]:
            best=(pr,k,pt)
    return best
pr,k,pt=single_xor_best(cipher)
pr,k,pt[:100], pt


(0.5074626865671642,
 121,
 b"\x01\x94Q\xe5\x9b'|\x99F9\x84sB\xba\xaesm\x8a\xf9?\x89I\xcf]u\x94~D'D\xf28\xb3AAt\x81\xcc\x03:\xb3\t\x132\x84}\xebh\r\x8b\xdeq\xda\xfb< \x97\xed\xe3\x97[,8\xbd\xc7\xd4.",
 b"\x01\x94Q\xe5\x9b'|\x99F9\x84sB\xba\xaesm\x8a\xf9?\x89I\xcf]u\x94~D'D\xf28\xb3AAt\x81\xcc\x03:\xb3\t\x132\x84}\xebh\r\x8b\xdeq\xda\xfb< \x97\xed\xe3\x97[,8\xbd\xc7\xd4.")

python
raw = r'''"description": "No\udb40\udd27\udb40\udd28\udb40\udd55\udb40\udd54\udb40\udd22\udb40\udd28 f\udb40\udd29\udb40\udd53\udb40\udd55\udb40\udd22\udb40\udd25\udb40\udd55i\udb40\udd20\udb40\udd25\udb40\udd55\udb40\udd20\udb40\udd23\udb40\udd56l\udb40\udd24\udb40\udd20\udb40\udd56\udb40\udd54\udb40\udd20\udb40\udd51e\udb40\udd23\udb40\udd52\udb40\udd53\udb40\udd23\udb40\udd54\udb40\udd27s\udb40\udd20\udb40\udd51\udb40\udd21\udb40\udd24\udb40\udd56\udb40\udd23 n\udb40\udd28\udb40\udd20\udb40\udd24\udb40\udd26\udb40\udd56\udb40\udd20e\udb40\udd23\udb40\udd20\udb40\udd52\udb40\udd26\udb40\udd22\udb40\udd24e\udb40\udd20\udb40\udd53\udb40\udd55\udb40\udd54\udb40\udd20\udb40\udd27d\udb40\udd23\udb40\udd54\udb40\udd25\udb40\udd55\udb40\udd23\udb40\udd54e\udb40\udd28\udb40\udd52\udb40\udd24\udb40\udd21\udb40\udd53\udb40\udd51d\udb40\udd23\udb40\udd28\udb40\udd23\udb40\udd28\udb40\udd20\udb40\udd54, h\udb40\udd56\udb40\udd28\udb40\udd52\udb40\udd25\udb40\udd27\udb40\udd51e\udb40\udd24\udb40\udd23\udb40\udd53\udb40\udd51r\udb40\udd27\udb40\udd20\udb40\udd26\udb40\udd51e\udb40\udd24\udb40\udd52\udb40\udd56\udb40\udd54 i\udb40\udd20\udb40\udd24\udb40\udd29\udb40\udd22s\udb40\udd21\udb40\udd21\udb40\udd27\udb40\udd24 y\udb40\udd56\udb40\udd22\udb40\udd51\udb40\udd27o\udb40\udd20\udb40\udd28\udb40\udd51\udb40\udd23u\udb40\udd28\udb40\udd22\udb40\udd24\udb40\udd25r\udb40\udd25\udb40\udd29\udb40\udd55\udb40\udd55 f\udb40\udd29\udb40\udd24\udb40\udd29\udb40\udd51l\udb40\udd55\udb40\udd55\udb40\udd22\udb40\udd22a\udb40\udd25\udb40\udd25\udb40\udd24\udb40\udd21g\udb40\udd53\udb40\udd24\udb40\udd52\udb40\udd55\ud83d\udc40\udb40\udd51\udb40\udd54\udb40\udd25\udb40\udd27\ufe0a"'''
obj = json.loads('{' + raw + '}')
desc = obj["description"]
vs = [ord(ch) for ch in desc if 0xFE00 <= ord(ch) <= 0xFE0F or 0xE0100 <= ord(ch) <= 0xE01EF]
vals = [(cp - 0xFE00) if 0xFE00<=cp<=0xFE0F else (cp-0xE0100+16) for cp in vs]
data = bytes(vals)
hexstr2 = data.decode('ascii').strip()
hexstr2, len(hexstr2)


('78ed289ce25e05e03f40fd0a3bc3d70a14f38046f030b6240ced073d5e3d8b41ca38380df8b57a43ca706a4bfd04921174f2a708a3824559ee949aee225541c4bead57',
 134)