INS'hAck CTF Write-up - s4tt01237’s diary

はじめに
Telegram [Misc]
gflag [Misc]
Dashlame - Part 1 [Rev]
intergover [Pwn]
signed or not signed [Pwn]
Yet Another RSA Challenge - Part 1 [Crypto]
まとめ

はじめに

2019/05/03 ~ 2019/05/06に開催されたINS'hAck CTFに参加しました．
初日しか参加してないので最終的な順位は分かりません．

Telegram [Misc]

Join our Telegram channel !

アプローチ：リンク先にとぶ

INSA{is_e2e_8annEd_1n_Russi4_too}

gflag [Misc]

My brother likes esoteric programming. He sent me this file but I don't see what it is for. Could you help me ?

> file gflag
gflag: ASCII text

アプローチ：gcode

> wc -l gflag
    1754 gflag

> head gflag
M73 P0 R2
M201 X9000 Y9000 Z500 E10000
M203 X500 Y500 Z12 E120
M204 P2000 R1500 T2000
M205 X10.00 Y10.00 Z0.20 E2.50
M205 S0 T0
M107
M115 U3.1.0
M83
M204 S2000 T1500

既視感があるなと思ったらNCプログラムでした(5,6年前にCNC旋盤使ったことがある)
(gcode だから gflagってことか〜)

適当なNCViewerに流すとflagが表示されます．

ncviewer.com

f:id:satto1237:20190507211816p:plain f:id:satto1237:20190507211852p:plain

INSA{3d_pr1nt3d_fl49}

Dashlame - Part 1 [Rev]

Can you try our new password manager ? There's a free flag in every password archive created !

This challenge contains a second part in the Crypto category.

> file dashlame.pyc
dashlame.pyc: python 2.7 byte-compiled

アプローチ：uncompyle

バイトコンパイルされたPythonファイルが渡されるのでとりあえずuncompyleします．

> uncompyle6 dashlame.pyc
# uncompyle6 version 3.2.6
# Python bytecode 2.7 (62211)
# Decompiled from: Python 2.7.15 |Anaconda, Inc.| (default, May  1 2018, 18:37:05)
# [GCC 4.2.1 Compatible Clang 4.0.1 (tags/RELEASE_401/final)]
# Embedded file name: dashlame.py
# Compiled at: 2019-04-17 06:56:53

from Crypto.Cipher import AES
import os, random, sys, sqlite3, time, zlib
HEADER = "      /.m.\\\n     /.mnnm.\\                                              ___\n    |.mmnvvnm.\\.                                     .,,,/`mmm.\\\n    |.mmnnvvnm.\\:;,.                           ..,,;;;/.mmnnnmm.\\\n    \\ mmnnnvvnm.\\::;;,                    .,;;;;;;;;/.mmmnnvvnnm.|\n     \\`mmnnnvvnm.\\::;::.sSSs      sSSs ,;;;;;;;;;;/.mmmnnvvvnnmm'/\n       \\`mmnnnvnm.\\:::::SSSS,,,,,,SSSS:::::::;;;/.mmmnnvvvnnmmm'/\n          \\`mnvvnm.\\::%%%;;;;;;;;;;;%%%%:::::;/.mnnvvvvnnmmmmm'/\n             \\`mmmm.%%;;;;;%%%%%%%%%%%%%%%::/.mnnvvvnnmmmmm'/ '\n                \\`%%;;;;%%%%s&&&&&&&&&s%%%%mmmnnnmmmmmm'/ '\n     |           `%;;;%%%%s&&.%%%%%%.%&&%mmmmmmmmmm'/ '\n\\    |    /       %;;%%%%&&.%;`    '%.&&%%%////// '\n  \\  |  /         %%%%%%s&.%%   x   %.&&%%%%%//%\n    \\  .:::::.  ,;%%%%s&&&&.%;     ;.&&%%%%%%%%/,\n-!!!- ::#:::::%%%%%%s&&&&&&&&&&&&&&&&&%%%%%%%%%%%\n    / :##:::::&&&&&&&&&&&&&&&&&&&&&%%%%%%%%%%%%%%,\n  /  | `:#:::&&&&&&&&&&&&&&&&&&&&&&&&%%%%%%%%%%%%%\n     |       `&&&&&&&&&,&&&&&&&&&&&&SS%%%%%%%%%%%%%\n               `~~~~~'~~        SSSSSSS%%%%%%%%%%%%%\n                               SSSSSSSS%%%%%%%%%%%%%%\n                              SSSSSSSSSS%%%%%%%%%%%%%.\n                            SSSSSSSSSSSS%%%%%%%%%%%%%%\n                          SSSSSSSSSSSSS%%%%%%%%%%%%%%%.\n                        SSSSSSSSSSSSSSS%%%%%%%%%%%%%%%%\n                      SSSSSSSSSSSSSSSS%%%%%%%%%%%%%%%%%.\n                    SSSSSSSSSSSSSSSSS%%%%%%%%%%%%%%%%%%%\n                  SSSSSSSSSSSSSSSSSS%%%%%%%%%%%%%%%%%%%%.\n\n                          WELCOME TO DASHLAME\n"
PEARSON_TABLE = [
 199, 229, 151, 178, 53, 6, 131, 42, 248, 110, 39, 28, 51, 216, 32, 14, 77, 34, 166, 213, 157, 150, 115, 197, 228, 221, 254, 172, 84, 27, 36, 156, 69, 96, 12, 220, 225, 137, 246, 141, 44, 208, 191, 109, 163, 21, 173, 250, 98, 227, 203, 162, 188, 3, 105, 171, 215, 15, 207, 218, 234, 56, 136, 235, 97, 79, 189, 102, 134, 11, 224, 117, 177, 222, 100, 129, 78, 18, 130, 187, 9, 184, 99, 108, 202, 13, 238, 17, 94, 70, 180, 144, 185, 168, 123, 71, 176, 91, 4, 153, 103, 242, 80, 127, 198, 82, 169, 148, 48, 120, 59, 55, 230, 209, 50, 73, 31, 49, 142, 149, 167, 249, 116, 1, 7, 86, 143, 101, 29, 52, 114, 154, 160, 128, 19, 170, 46, 214, 38, 67, 186, 252, 181, 145, 212, 183, 22, 231, 107, 43, 47, 122, 251, 217, 5, 62, 88, 244, 200, 93, 240, 219, 124, 58, 161, 89, 211, 158, 247, 60, 236, 65, 106, 113, 66, 81, 165, 194, 223, 40, 233, 126, 139, 72, 132, 61, 135, 57, 87, 182, 164, 35, 159, 118, 8, 83, 210, 243, 104, 76, 75, 119, 90, 138, 20, 206, 95, 16, 74, 33, 245, 237, 111, 64, 253, 125, 23, 232, 193, 37, 175, 92, 30, 241, 255, 133, 0, 140, 2, 155, 85, 10, 146, 179, 25, 26, 226, 201, 195, 121, 190, 63, 68, 152, 45, 147, 41, 204, 192, 205, 196, 54, 174, 239, 112, 24]

def pad(s):
    mark = chr(16 - len(s) % 16)
    while len(s) % 16 != 15:
        s += chr(random.randint(0, 255))

    return s + mark


def unpad(s):
    return s[:-ord(s[-1])]


def get_random_passphrase():
    sys.stdout.write('Getting random data from atmospheric noise and mouse movements')
    sys.stdout.flush()
    for i in range(10):
        sys.stdout.write('.')
        sys.stdout.flush()
        time.sleep(random.randint(1, 20) / 10.0)

    print ''
    with open('wordlist.txt', 'rb') as (fi):
        passwords = fi.read().strip().split('\n')
    return (random.choice(passwords), random.choice(passwords))


def get_pearson_hash(passphrase):
    key, iv = ('', '')
    for i in range(32):
        h = (i + ord(passphrase[0])) % 256
        for c in passphrase[1:]:
            h = PEARSON_TABLE[h ^ ord(c)]

        if i < 16:
            key += chr(h)
        else:
            iv += chr(h)

    return (
     key, iv)


def encrypt_stream(data, passphrase):
    key, iv = get_pearson_hash(passphrase)
    aes = AES.new(key, AES.MODE_CBC, iv)
    data = pad(data)
    return aes.encrypt(data)


def decrypt_stream(data, passphrase):
    key, iv = get_pearson_hash(passphrase)
    aes = AES.new(key, AES.MODE_CBC, iv)
    data = unpad(aes.decrypt(data))
    return data


def encrypt_archive(archive_filename, passphraseA, passphraseB):
    with open(archive_filename, 'rb') as (db_fd):
        with open(archive_filename.replace('.db', '.dla'), 'wb') as (dla_fd):
            enc1 = encrypt_stream(db_fd.read(), passphraseA)
            enc2 = encrypt_stream(enc1, passphraseB)
            dla_fd.write(enc2)
    os.unlink(archive_filename)


def decrypt_archive(archive_filename, passphraseA, passphraseB):
    with open(archive_filename, 'rb') as (dla_fd):
        with open(archive_filename.replace('.dla', '.db'), 'wb') as (db_fd):
            dec1 = decrypt_stream(dla_fd.read(), passphraseB)
            dec2 = decrypt_stream(dec1, passphraseA)
            db_fd.write(dec2)
    os.unlink(archive_filename)


def createArchive():
    archive_name = raw_input('Please enter your archive name: ')
    passphraseA, passphraseB = get_random_passphrase()
    print 'This is your passphrase :', passphraseA, passphraseB
    print 'Please remember it or you will lose all your passwords.'
    archive_filename = archive_name + '.db'
    with open(archive_filename, 'wb') as (db_fd):
        db_fd.write(zlib.decompress('x\x9c\x0b\x0e\xf4\xc9,IUH\xcb/\xcaM,Q0f`a`ddpPP````\x82b\x18`\x04b\x164>!\xc0\xc4\xa0\xfb\x8c\x9b\x17\xa4\x98y.\x03\x10\x8d\x82Q0\n\x88\x05\x89\x8c\xec\xe2\xf2\xf2\x8c\x8d\x82%\x89I9\xa9\x01\x89\xc5\xc5\xe5\xf9E)\xc5p\x06\x93s\x90\xabc\x88\xabB\x88\xa3\x93\x8f\xab\x02\\X\xa3<5\xa9\x18\x94\xabC\\#Bt\x14J\x8bS\x8b\xf2\x12sa\xdc\x02\xa820W\x13\x927\xcf0\x00\xd1(\x18\x05\xa3`\x08\x03#F\x16mYkh\xe6\x8fO\xadH\xcc-\xc8I\x85\xe5~O\xbf`\xc7\xea\x90\xcc\xe2\xf8\xa4\xd0\x92\xf8\xc4\xf8`\xe7"\x93\x92\xe4\x8cZ\x00\xa8&=\x8f'))
    encrypt_archive(archive_filename, passphraseA, passphraseB)
    print 'Archive created successfully.'


def updateArchive():
    archive_name = raw_input('Please enter your archive name: ')
    passphrase = raw_input('Please enter your passphrase: ')
    passphraseA, passphraseB = passphrase.split()
    website = raw_input('Website: ')
    username = raw_input('Username: ')
    password = raw_input('Password: ')
    dla_filename = archive_name + '.dla'
    db_filename = archive_name + '.db'
    decrypt_archive(dla_filename, passphraseA, passphraseB)
    conn = sqlite3.connect(db_filename)
    cur = conn.cursor()
    cur.execute('INSERT INTO Passwords VALUES(?,?,?)', (website, username, password))
    conn.commit()
    conn.close()
    encrypt_archive(db_filename, passphraseA, passphraseB)
    print 'Update done.'


def accessArchive():
    archive_name = raw_input('Please enter your archive name: ')
    passphrase = raw_input('Please enter your passphrase: ')
    passphraseA, passphraseB = passphrase.split()
    website = raw_input('Website: ')
    dla_filename = archive_name + '.dla'
    db_filename = archive_name + '.db'
    decrypt_archive(dla_filename, passphraseA, passphraseB)
    conn = sqlite3.connect(db_filename)
    cur = conn.cursor()
    cur.execute('SELECT Username, Password FROM Passwords WHERE Website=?', (website,))
    results = cur.fetchall()
    conn.close()
    encrypt_archive(db_filename, passphraseA, passphraseB)
    if len(results) == 0:
        print 'No results.'
    else:
        for result in results:
            print result[0], ':', result[1]


if __name__ == '__main__':
    print HEADER
    print '1. Create a new password archive'
    print '2. Add a password to an archive'
    print '3. Access a password from an existing archive'
    try:
        res = raw_input()
        if res == '1':
            createArchive()
        else:
            if res == '2':
                updateArchive()
            else:
                if res == '3':
                    accessArchive()
                else:
                    print 'Wrong choice'
    except:
        print 'Error.'

ぱっと見dbファイル作成してあれこれしてっるぽいですね．

パスワードアーカイブ作成

> python dashlame.py
      /.m.\
     /.mnnm.\                                              ___
    |.mmnvvnm.\.                                     .,,,/`mmm.\
    |.mmnnvvnm.\:;,.                           ..,,;;;/.mmnnnmm.\
    \ mmnnnvvnm.\::;;,                    .,;;;;;;;;/.mmmnnvvnnm.|
     \`mmnnnvvnm.\::;::.sSSs      sSSs ,;;;;;;;;;;/.mmmnnvvvnnmm'/
       \`mmnnnvnm.\:::::SSSS,,,,,,SSSS:::::::;;;/.mmmnnvvvnnmmm'/
          \`mnvvnm.\::%%%;;;;;;;;;;;%%%%:::::;/.mnnvvvvnnmmmmm'/
             \`mmmm.%%;;;;;%%%%%%%%%%%%%%%::/.mnnvvvnnmmmmm'/ '
                \`%%;;;;%%%%s&&&&&&&&&s%%%%mmmnnnmmmmmm'/ '
     |           `%;;;%%%%s&&.%%%%%%.%&&%mmmmmmmmmm'/ '
\    |    /       %;;%%%%&&.%;`    '%.&&%%%////// '
  \  |  /         %%%%%%s&.%%   x   %.&&%%%%%//%
    \  .:::::.  ,;%%%%s&&&&.%;     ;.&&%%%%%%%%/,
-!!!- ::#:::::%%%%%%s&&&&&&&&&&&&&&&&&%%%%%%%%%%%
    / :##:::::&&&&&&&&&&&&&&&&&&&&&%%%%%%%%%%%%%%,
  /  | `:#:::&&&&&&&&&&&&&&&&&&&&&&&&%%%%%%%%%%%%%
     |       `&&&&&&&&&,&&&&&&&&&&&&SS%%%%%%%%%%%%%
               `~~~~~'~~        SSSSSSS%%%%%%%%%%%%%
                               SSSSSSSS%%%%%%%%%%%%%%
                              SSSSSSSSSS%%%%%%%%%%%%%.
                            SSSSSSSSSSSS%%%%%%%%%%%%%%
                          SSSSSSSSSSSSS%%%%%%%%%%%%%%%.
                        SSSSSSSSSSSSSSS%%%%%%%%%%%%%%%%
                      SSSSSSSSSSSSSSSS%%%%%%%%%%%%%%%%%.
                    SSSSSSSSSSSSSSSSS%%%%%%%%%%%%%%%%%%%
                  SSSSSSSSSSSSSSSSSS%%%%%%%%%%%%%%%%%%%%.

                          WELCOME TO DASHLAME

1. Create a new password archive
2. Add a password to an archive
3. Access a password from an existing archive
1
Please enter your archive name: cawayui
Getting random data from atmospheric noise and mouse movements..........
This is your passphrase : sabally discombobulation
Please remember it or you will lose all your passwords.
Archive created successfully.

パスワード追加

[snip]

1. Create a new password archive
2. Add a password to an archive
3. Access a password from an existing archive
2
Please enter your archive name: cawayui
Please enter your passphrase: sabally discombobulation
Website: satto.hatenadiary.com
Username: satto1237
Password: pass
Update done.

パスワード確認

[snip]

1. Create a new password archive
2. Add a password to an archive
3. Access a password from an existing archive
3
Please enter your archive name: cawayui
Please enter your passphrase: sabally discombobulation
Website: satto.hatenadiary.com
satto1237 : pass

生成ファイル確認

> file cawayui.dla
cawayui.dla: data

> head cawayui.dla
IZ���]6���)��9-ei�l�00���ײZ��A\�L�
eKFp�1�G&z]�S�0��9��
>D�����OFK��` ��O��0{��    �{��̵�_FZ
�ןy�|g��
{>�z�A������}yX����>�%oH�"�f7�y�i�^�0"M��AF�=�ʋT�dA�&W|?�w�������R��:{Y,�H� �xM�j�
����S\�0����/(�D��'���� 9��?]#���Ṳ���1
Q��OI��ퟳ  �e���8R�A���y�*��q�-A������i�#zѕp!e��/]gv��U�t�5��7�#�RXD
                                                                         ���B�#�J�m�&�߯��30M�x���o�B+��(�"S�Ow�K��
Q"~�                                                                                                             �^1��%"1N�[�MR�+q̏Fm"��.�GbY��
NN}S������b��$|����)`�R�B��<��#���{��j�d���?>�H��)q-�x���Eԩ  !��i��s�A>i������n�l?�U�#�0�g
Tէ�v{O��y�|χ+�ƒ&[�_�;�.!җ��o'��[�%���:$
2UfjW�j�4{�qjƥB���.�{aj���]?.���;g$W�d���ūm���;wM�BY����]C��ޖ Ns�)[�I�y-r(��f�U�o
I4ٱ*ݢ(&à-N�E�^0���,���|ť������~Ae8X�:y���"沬��B{�k�Ka%�I���    �����^޽ٱux� ��?���[�љ���[�]��    ^(���UÒ�,:�����o��⪻�B�R�7�õXM]r5�P��O�Q����]��z���L2��O�����-B���
        �N��W;a�
                �P���f��L��FkYU�Xt�T���,������j��ς8G!�?�mvW��Ȩ�w���.���|����`y5�&�
                                                                                   S�{�1o����+ũ]/nڎ�    �

ソースコードを読む限り新しいアーカイブを作成するときに謎データを書き込んでいるのでAddしたユーザとパスワード以外にもユーザデータが存在すると考えられます．
また，accessArchive内でデータを読み出した後(decrypt_archiveした後)にencrypt_archiveしているためこの処理をコメントアウトすることでdecryptされたdbファイルにアクセスできるようになることが分かります．

> sqlite3
sqlite> .open cawayui.db
sqlite> .tables
Passwords
sqlite> .schema
CREATE TABLE Passwords(website TEXT, username TEXT, password TEXT);
sqlite> SELECT * FROM Passwords;
website_example|username|INSA{Tis_bUt_a_SCr4tch}
satto.hatenadiary.com|satto1237|pass

INSA{Tis_bUt_a_SCr4tch}

intergover [Pwn]

I hope you know how integers are stored.

ssh -i <your_keyfile> -p 2223 user@intergover.ctf.insecurity-insa.fr To find your keyfile, look into your profile on this website.

> ssh -i ~/.ssh/id_inshack -p 2223 user@intergover.ctf.insecurity-insa.fr
 ___           _   _            _      ____   ___  _  ___
|_ _|_ __  ___| | | | __ _  ___| | __ |___ \ / _ \/ |/ _ \
| || '_ \/ __| |_| |/ _` |/ __| |/ /   __) | | | | | (_) |
| || | | \__ \  _  | (_| | (__|   <   / __/| |_| | |\__, |
|___|_| |_|___/_| |_|\__,_|\___|_|\_\ |_____|\___/|_|  /_/

===========================================================

      You are accessing a sandbox challenge over SSH
        This sandbox will be killed soon enough.
       Please wait while we launch your sandbox...

===========================================================

Give me one param: 1127
No, I can't give you the flag: 1127

アプローチ：読む

与えられたバイナリファイルをidaで開くと242をパラメータとして与えればいいことが分かります．

f:id:satto1237:20190507221625p:plain

[snip]

Give me one param: 242
INSA{B3_v3rY_c4r3fUL_w1tH_uR_1nt3g3r_bR0}

INSA{B3_v3rY_c4r3fUL_w1tH_uR_1nt3g3r_bR0}

signed or not signed [Pwn]

Signed or not signed, this is the question :) ssh -i <your_keyfile> -p 2228 user@signed-or-not-signed.ctf.insecurity-insa.fr To find your keyfile, look into your profile on this website.

アプローチ：unsigned

> ssh -i ~/.ssh/id_inshack -p 2228 user@signed-or-not-signed.ctf.insecurity-insa.fr
- ___           _   _            _      ____   ___  _  ___
|_ _|_ __  ___| | | | __ _  ___| | __ |___ \ / _ \/ |/ _ \
| || '_ \/ __| |_| |/ _` |/ __| |/ /   __) | | | | | (_) |
| || | | \__ \  _  | (_| | (__|   <   / __/| |_| | |\__, |
|___|_| |_|___/_| |_|\__,_|\___|_|\_\ |_____|\___/|_|  /_/

===========================================================

      You are accessing a sandbox challenge over SSH
        This sandbox will be killed soon enough.
       Please wait while we launch your sandbox...

===========================================================

Please give me a number: 1127
Bro, it's really too big.

とりあえず与えられたバイナリファイルをidaで開きます．

f:id:satto1237:20190507233230p:plain

f:id:satto1237:20190507234941p:plain

10以下かつ64870である数値を入力しなければいけませんがunsignedであることを利用すればいけます．

[snip]

Please give me a number:-666
INSA{Th3_qU3sTi0n_1s_S1gN3d_0r_x90}
Connection to signed-or-not-signed.ctf.insecurity-insa.fr closed.

INSA{Th3_qU3sTi0n_1s_S1gN3d_0r_x90}

Yet Another RSA Challenge - Part 1 [Crypto]

Buy an encrypted flag, get a (almost intact) prime factor for free !

You can find a harder version of this challenge in the Programming category.

import subprocess
p = subprocess.check_output('openssl prime -generate -bits 2048 -hex')
q = subprocess.check_output('openssl prime -generate -bits 2048 -hex')
flag = int('INSA{REDACTED}'.encode('hex'), 16)

N = int(p,16) * int(q,16)
print N
print '0x'+p.replace('9F','FC')
print pow(flag,65537,N)

719579745653303119025873098043848913976880838286635817351790189702008424828505522253331968992725441130409959387942238566082746772468987336980704680915524591881919460709921709513741059003955050088052599067720107149755856317364317707629467090624585752920523062378696431510814381603360130752588995217840721808871896469275562085215852034302374902524921137398710508865248881286824902780186249148613287250056380811479959269915786545911048030947364841177976623684660771594747297272818410589981294227084173316280447729440036251406684111603371364957690353449585185893322538541593242187738587675489180722498945337715511212885934126635221601469699184812336984707723198731876940991485904637481371763302337637617744175461566445514603405016576604569057507997291470369704260553992902776099599438704680775883984720946337235834374667842758010444010254965664863296455406931885650448386682827401907759661117637294838753325610213809162253020362015045242003388829769019579522792182295457962911430276020610658073659629786668639126004851910536565721128484604554703970965744790413684836096724064390486888113608024265771815004188203124405817878645103282802994701531113849607969243815078720289912255827700390198089699808626116357304202660642601149742427766381
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
596380963583874022971492302071822444225514552231574984926542429117396590795270181084030717066220888052607057994262255729890598322976783889090993129161030148064314476199052180347747135088933481343974996843632511300255010825580875930722684714290535684951679115573751200980708359500292172387447570080875531002842462002727646367063816531958020271149645805755077133231395881833164790825731218786554806777097126212126561056170733032553159740167058242065879953688453169613384659653035659118823444582576657499974059388261153064772228570460351169216103620379299362366574826080703907036316546232196313193923841110510170689800892941998845140534954264505413254429240789223724066502818922164419890197058252325607667959185100118251170368909192832882776642565026481260424714348087206462283972676596101498123547647078981435969530082351104111747783346230914935599764345176602456069568419879060577771404946743580809330315332836749661503035076868102720709045692483171306425207758972682717326821412843569770615848397477633761506670219845039890098105484693890695897858251238713238301401843678654564558196040100908796513657968507381392735855990706254646471937809011610992016368630851454275478216664521360246605400986428230407975530880206404171034278692756

アプローチ：全探索

配布されたプログラムを確認すると素数pの9FをFCに置換していることが分かります．
置換後のpのFCの出現数は4なので元々FCだった場合も考慮し計算すると置換前のパターン数は16になることが分かります．
あとは全探索して正規のpを見つければ終わりです．

以下が頭ガバガバソルバです．

#!/usr/bin/env python3
# -*- coding: utf-8 -*-

from Crypto.Util.number import *

str_p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
n = 719579745653303119025873098043848913976880838286635817351790189702008424828505522253331968992725441130409959387942238566082746772468987336980704680915524591881919460709921709513741059003955050088052599067720107149755856317364317707629467090624585752920523062378696431510814381603360130752588995217840721808871896469275562085215852034302374902524921137398710508865248881286824902780186249148613287250056380811479959269915786545911048030947364841177976623684660771594747297272818410589981294227084173316280447729440036251406684111603371364957690353449585185893322538541593242187738587675489180722498945337715511212885934126635221601469699184812336984707723198731876940991485904637481371763302337637617744175461566445514603405016576604569057507997291470369704260553992902776099599438704680775883984720946337235834374667842758010444010254965664863296455406931885650448386682827401907759661117637294838753325610213809162253020362015045242003388829769019579522792182295457962911430276020610658073659629786668639126004851910536565721128484604554703970965744790413684836096724064390486888113608024265771815004188203124405817878645103282802994701531113849607969243815078720289912255827700390198089699808626116357304202660642601149742427766381
e = 65537
c = 596380963583874022971492302071822444225514552231574984926542429117396590795270181084030717066220888052607057994262255729890598322976783889090993129161030148064314476199052180347747135088933481343974996843632511300255010825580875930722684714290535684951679115573751200980708359500292172387447570080875531002842462002727646367063816531958020271149645805755077133231395881833164790825731218786554806777097126212126561056170733032553159740167058242065879953688453169613384659653035659118823444582576657499974059388261153064772228570460351169216103620379299362366574826080703907036316546232196313193923841110510170689800892941998845140534954264505413254429240789223724066502818922164419890197058252325607667959185100118251170368909192832882776642565026481260424714348087206462283972676596101498123547647078981435969530082351104111747783346230914935599764345176602456069568419879060577771404946743580809330315332836749661503035076868102720709045692483171306425207758972682717326821412843569770615848397477633761506670219845039890098105484693890695897858251238713238301401843678654564558196040100908796513657968507381392735855990706254646471937809011610992016368630851454275478216664521360246605400986428230407975530880206404171034278692756
index = [11, 143, 475, 499]


def searchP(s, d):
    if d == 4:
        p = int(s,16)
        if n % p == 0:
            print(p)
    else:
        searchP(s[:index[d]] + 'FC' + s[index[d]+2:], d + 1)
        searchP(s[:index[d]] + '9F' + s[index[d]+2:], d + 1)

def solve():
    p = 27869881035956015184979178092922248885674897320108269064145135676677416930908750101386898785101159450077433625380803555071301130739332256486285289470097290409044426739584302074834857801721989648648799253740641480496433764509396039330395579654527851232078667173592401475356727873045602595552393666889257027478385213547302885118341490346766830846876201911076530008127691612594913799272782226366932754058372641521481522494577124999360890113778202218378165756595787931498460866236502220175258385407478826827807650036729385244897815805427164434537088709092238894902485613707990645011133078730017425033369999448757627854563
    q = n // p
    phi = (p - 1) * (q - 1)
    d = inverse(e, phi)
    m = pow(c, d, n)
    print(long_to_bytes(m))

if __name__ == '__main__':
    searchP(str_p, 0)
    solve()

27869881035956015184979178092922248885674897320108269064145135676677416930908750101386898785101159450077433625380803555071301130739332256486285289470097290409044426739584302074834857801721989648648799253740641480496433764509396039330395579654527851232078667173592401475356727873045602595552393666889257027478385213547302885118341490346766830846876201911076530008127691612594913799272782226366932754058372641521481522494577124999360890113778202218378165756595787931498460866236502220175258385407478826827807650036729385244897815805427164434537088709092238894902485613707990645011133078730017425033369999448757627854563
b'INSA{I_w1ll_us3_OTp_n3xT_T1M3}'

INSA{I_w1ll_us3_OTp_n3xT_T1M3}

まとめ

また簡単な問題しかとけなかった
べんきょうする