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题目： OBZXGZL3NFVHOZTLMUWTANRQGYZDMMJYGE4H2=== 情报显示，...

Erstellt am: 17. Juni 2026

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Frage

题目：
OBZXGZL3NFVHOZTLMUWTANRQGYZDMMJYGE4H2===
情报显示，这份文件经过了多层的加密保护，使用了古典密码学中多种经典算法的组合。你需要运用你全部的密码学知识来逐层破解它！

提示：
第一层OBZXGZL3NFVHOZTLMUWTANRQGYZDMMJYGE4H2===是用base32解码得psse{ijwfke-0606261818}但这不是最终得flag

帮我找到flag

Python

python
import string
s='psse{ijwfke-0606261818}'
alpha=string.ascii_lowercase
for shift in range(26):
    trans=str.maketrans(alpha, alpha[shift:]+alpha[:shift])
    print(shift, s.translate(trans))

Python

python
def atbash(s):
    res=''
    for ch in s:
        if ch in alpha: res+=alpha[25-alpha.index(ch)]
        else: res+=ch
    return res
a=atbash(s)
print(a)
for shift in range(26):
    print(shift, a.translate(str.maketrans(alpha, alpha[shift:]+alpha[:shift])))

Python

python
s='psse{ijwfke-0606261818}'
len(s), list(enumerate(s))


(23,
 [(0, 'p'),
  (1, 's'),
  (2, 's'),
  (3, 'e'),
  (4, '{'),
  (5, 'i'),
  (6, 'j'),
  (7, 'w'),
  (8, 'f'),
  (9, 'k'),
  (10, 'e'),
  (11, '-'),
  (12, '0'),
  (13, '6'),
  (14, '0'),
  (15, '6'),
  (16, '2'),
  (17, '6'),
  (18, '1'),
  (19, '8'),
  (20, '1'),
  (21, '8'),
  (22, '}')])

Python

python
def vigenere_decrypt(ct,key):
    res=''; j=0
    for ch in ct:
        if ch in alpha:
            res+=alpha[(alpha.index(ch)-alpha.index(key[j%len(key)]))%26]; j+=1
        else:
            res+=ch
    return res
for key in ['key','ctf','flag','crypto','cipher','classical','caesar','vigenere','base','bacon','railfence','rail','atbash','rot']:
    print(key, vigenere_decrypt(s,key))

Python

python
digits='0606261818'
def decrypt_digit_key(ct,digs):
    res=''; j=0
    for ch in ct:
        if ch in alpha:
            d=int(digs[j%len(digs)])
            # single digit shifts
            res+=alpha[(alpha.index(ch)-d)%26]; j+=1
        else: res+=ch
    return res
print(decrypt_digit_key('psseijwfke',digits))
# use pairs 06,06,26,18,18 mod 26
pairs=[6,6,26,18,18]
res=''
for i,ch in enumerate('psseijwfke'):
    res+=alpha[(alpha.index(ch)-pairs[i%len(pairs)])%26]
print(res)
# use pairs encrypt? 
print('enc pairs',''.join(alpha[(alpha.index(ch)+pairs[i%len(pairs)])%26] for i,ch in enumerate('psseijwfke')))

Python

python
for key in ['ffzrr','ggasi','0606261818','06061818','ffsrr','ffzrr']:
    keyletters=''.join(c for c in key if c.isalpha()).lower() or ''.join(alpha[int(d)%26] for d in key if d.isdigit())
    print(key,keyletters,vigenere_decrypt('psseijwfke',keyletters))

Python

python
def rail_fence_decrypt(cipher, rails):
    # standard zigzag
    if rails==1: return cipher
    # pattern indices
    pattern=list(range(rails))+list(range(rails-2,0,-1))
    rail_nums=[pattern[i%len(pattern)] for i in range(len(cipher))]
    counts=[rail_nums.count(r) for r in range(rails)]
    rails_str=[]
    pos=0
    for c in counts:
        rails_str.append(list(cipher[pos:pos+c])); pos+=c
    out=[]
    pointers=[0]*rails
    for r in rail_nums:
        out.append(rails_str[r][pointers[r]]); pointers[r]+=1
    return ''.join(out)
for r in range(2,12):
    t=rail_fence_decrypt(s,r)
    print(r, t)

Python

python
letters='psseijwfke'
for r in range(2,8):
    print(r, rail_fence_decrypt(letters,r))

Python

python
def rail_fence_encrypt(text, rails):
    if rails==1: return text
    pattern=list(range(rails))+list(range(rails-2,0,-1))
    rails_str=['' for _ in range(rails)]
    for i,ch in enumerate(text):
        rails_str[pattern[i%len(pattern)]]+=ch
    return ''.join(rails_str)
for r in range(2,8):
    print(r, rail_fence_encrypt(s,r), rail_fence_encrypt(letters,r))

Python

python
cts='psseijwfke'
candidates=['cipher','secret','crypto','caesar','decode','encode','hidden','answer','puzzle','vigenr','vigenere','classi','atbash','affine','simple','double','threee','base32','railfe','riddle','dragon','attack','ceshi','jiefu','ctfxxx','origin','middle','format']
def key_for(pt, ct=cts):
    ks=[]
    for c,p in zip(ct,pt):
        ks.append(alpha[(alpha.index(c)-alpha.index(p))%26])
    return ''.join(ks)
for cand in candidates:
    pt='flag'+cand[:6]
    k=key_for(pt)
    print(pt,k)

Python

python
import string, math
alpha=string.ascii_lowercase
def mat_inv2(M, mod=26):
    a,b=M[0]; c,d=M[1]
    det=(a*d-b*c)%mod
    invdet=pow(det,-1,mod)
    return [[d*invdet%mod, (-b)*invdet%mod],[(-c)*invdet%mod, a*invdet%mod]]
def hill_dec_letters(ct,M):
    Minv=mat_inv2(M)
    nums=[alpha.index(ch) for ch in ct]
    out=''
    for i in range(0,len(nums),2):
        x,y=nums[i],nums[i+1]
        p=(Minv[0][0]*x+Minv[0][1]*y)%26
        q=(Minv[1][0]*x+Minv[1][1]*y)%26
        out+=alpha[p]+alpha[q]
    return out
for M in [[[12,3],[3,5]],[[25,16],[3,5]]]:
    print(M, mat_inv2(M), hill_dec_letters('psseijwfke',M))

Python

python
for word in ['nujgoi','ahwtoi']:
    print(word)
    for k in range(26):
        rotw=rot(word,k)
        if any(x in rotw for x in ['cipher','secret','caesar','answer','crypto','hidden','flag','decode','attack','matrix']):
            print(k,rotw)
    print('atbash',atbash(word))
    for k in range(26):
        w=rot(atbash(word),k)
        if any(x in w for x in ['cipher','secret','caesar','answer','crypto','hidden','flag','decode','attack','matrix']):
            print('ab',k,w)

Python

python
for w in ['nujgoi','ahwtoi']:
    print(w, 'single', decrypt_digit_key(w,digits))
    pairs=[6,6,26,18,18]
    print('pairs dec', ''.join(alpha[(alpha.index(ch)-pairs[i%len(pairs)])%26] for i,ch in enumerate(w)))
    print('pairs enc', ''.join(alpha[(alpha.index(ch)+pairs[i%len(pairs)])%26] for i,ch in enumerate(w)))

Python

python
def det_inv(M):
    a,b=M[0]; c,d=M[1]
    det=(a*d-b*c)%26
    return math.gcd(det,26)==1,det
keys={'hill':[[7,8],[11,11]],'gybnqkurp':[[6,24],[1,13]],'test':[[19,4],[18,19]],'abcd':[[0,1],[2,3]],'0606':[[0,6],[0,6]],'2618':[[2,6],[1,8]],'khsy':[[10,7],[18,24]],'keys':[[10,4],[24,18]]}
for k,M in keys.items():
    ok,det=det_inv(M)
    if ok:
        print(k,M,hill_dec_letters('psseijwfke',M))
    else: print(k,M,'noninvertible det',det)

Python

python
dig='0606261818'
for r in range(2,7):
    print(r, rail_fence_decrypt(dig,r), rail_fence_encrypt(dig,r))

Python

python
def transforms_word(w):
    results=[]
    funcs=[('id',lambda x:x),('rev',lambda x:x[::-1]),('atbash',atbash),('atbashrev',lambda x:atbash(x)[::-1]),('revatbash',lambda x:atbash(x[::-1]))]
    for name,f in funcs:
        t=f(w)
        for k in range(26):
            results.append((name+' rot'+str(k), rot(t,k)))
    return results
wordlist=['secret','cipher','crypto','caesar','decode','encode','hidden','answer','puzzle','attack','matrix','affine','atbash','letter','number','common','simple','classi','double','flagxx','passwd','phrase','keykey','rotrot','baconx','morsex','railxx']
for w in ['nujgoi','ahwtoi']:
    for name,u in transforms_word(w):
        if u in wordlist:
            print(w,name,u)
    # contains approximate? print all maybe
    print('examples for',w)
    for name,u in transforms_word(w)[:10]:
        pass

Python

python
import pkgutil, sys
mods=['wordfreq','wordninja','wordfreq','wordnet','wordfreq']
print([m for m in mods if pkgutil.find_loader(m)])

Python

python
from collections import deque

s='psse{ijwfke-0606261818}'
alpha='abcdefghijklmnopqrstuvwxyz'

def apply_letters_only(text, func):
    letters=[ch for ch in text if ch in alpha]
    new=func(''.join(letters))
    it=iter(new)
    return ''.join(next(it) if ch in alpha else ch for ch in text)

def ops(text):
    outs=[]
    # rot all except 0? 
    for k in range(1,26):
        outs.append((f'rot{k}', rot(text,k)))
    outs.append(('atbash', atbash(text)))
    outs.append(('reverse', text[::-1]))
    for r in range(2,12):
        outs.append((f'raildec{r}', rail_fence_decrypt(text,r)))
        outs.append((f'railenc{r}', rail_fence_encrypt(text,r)))
        outs.append((f'letters_raildec{r}', apply_letters_only(text, lambda

(0, 74694)

Python

python
pat=''.join('a' if ch in 'aeiou' else 'b' for ch in 'psseijwfke')
print(pat)
def bacon_decode(pat):
    outs=[]
    for flip in [False,True]:
        letters=''
        for i in range(0,len(pat),5):
            group=pat[i:i+5]
            if len(group)<5: continue
            bits=''.join(('1' if c=='b' else '0') for c in group)
            if flip:
                bits=''.join('1' if b=='0' else '0' for b in bits)
            val=int(bits,2)
            letters+=alpha[val] if val<26 else '?'
        outs.append((flip,letters))
    return outs
print(bacon_decode(pat))

Python

python
keys=['key','ctf','flag','crypto','cipher','classical','classic','caesar','vigenere','base','base32','bacon','railfence','rail','atbash','rot','hill','playfair','secret','password','matrix','decode','encode','affine','morse','polybius','keyboard','number','date','khsy','ffzrr','ggass','0606261818']
def vig(text,key,mode='dec'):
    res=''; j=0
    for ch in text:
        if ch in alpha:
            k=alpha.index(key[j%len(key)])
            x=alpha.index(ch)
            res+=alpha[(x-k)%26] if mode=='dec' else alpha[(x+k)%26]
            j+=1
        else: res+=ch
    return res
def beaufort(text,key): # plaintext = key - cipher? decryption same
    res=''; j=0
    for ch

Gedanke

Decoding the cipher using classical methods

I found the solution: Applying ROT8 and then the Beaufort cipher with the key "classic" gives the expected flag{crypto-0606261818}! The steps involve decoding from Base32, applying ROT8 for Caesar shift, and then decrypting with Beaufort. The "classic" key fits the clue from "古典密码学," confirming the sequence.

Thought for 12m 5s

Antwort

最终 flag 是：

text
flag{crypto-0606261818}

破解链路：

text
OBZXGZL3NFVHOZTLMUWTANRQGYZDMMJYGE4H2===
↓ Base32 解码
psse{ijwfke-0606261818}
↓ 凯撒位移 +8 / ROT8
xaam{qrensm-0606261818}
↓ Beaufort 密码，key = classic
flag{crypto-0606261818}

所以提交：

text
flag{crypto-0606261818}

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