PicoCTF 2014 Tyrannosaurus Hex, NoComment

Write-up cuộc thi picoCTF 2014

5 challenge đầu tiên:

1.  Tyrannosaurus Hex 
2.  No Comment
3.  Caesar
4.  The Valley of Fear

Tyrannosaurus Hex - 10
      Đây là challenge đầu tiên. Bạn phải hoàn thành thì các challenge tiếp theo mới hiện ra.

The contents of the flash drive appear to be password protected. On the back of the flash drive, you see the hexadecimal number 0xe06a9ff3 scribbled in ink. The password prompt, however, only accepts decimal numbers. What number should you enter? (Press the Hint button for advice on solving the challenge)

   Tóm tắt là đề bài đưa cho bạn một số dưới dạng hexa. Yêu cầu bạn tìm  số đó được viết dưới dạng thập phân.
   Đề bài quá đơn giản, ta có thể sử dụng các tool trên mạng để làm điều này. Ví dụ: http://www.mathsisfun.com/binary-decimal-hexadecimal-converter.html
   Và kết quả: 3765084147

No Comment - 20

The CD you find has a copy of your father's website: homepage.html. Maybe something is hidden in the site...

   Đề bài cho ta một link, và gợi ý có một vài thứ được ẩn trong đó. Tất nhiên yêu cầu là tìm được thông điệp ẩn rồi. :D
   Truy cập vào homepage.html. Sau đó xem mã nguồn của trang này.
Và đây là điều mà chúng ta cần.

The password for this site is: flag_2b2c7cae0da7a4088ca30114a4b9ed729e5490f4

Caesar

You find an encrypted message written on the documents. Can you decrypt it?
encrypted.txt

   Một file encrypted.txt Và nhiệm vụ chúng ta ở đây là giải mã nó để tìm chuỗi bí mật.
   Nội dung file:

uiftfdsfuqbttqisbtfjtpgtqyrdhekuqsxjdtvyvkghlpvkfml 

   Với tiêu đề của challenge này là Caesar. Ta nghĩ ngay đến thuật toán caesar ( tôi quen gọi là dịch vòng). Bạn có thể đọc thêm tại đây: http://vi.wikipedia.org/wiki/Mat_ma_Caesar
   Ở đây do không biết nội dung file được mã hóa dịch vòng bao nhiêu lần nên tôi sử dụng http://planetcalc.com/1434/ để decrypt nó.
  Sau khi nhân Calculate ta được kết quả như sau:

ROT0 uiftfdsfuqbttqisbtfjtpgtqyrdhekuqsxjdtvyvkghlpvkfml
ROT1 vjgugetgvrcuurjtcugkuqhurzseiflvrtykeuwzwlhimqwlgnm
ROT2 wkhvhfuhwsdvvskudvhlvrivsatfjgmwsuzlfvxaxmijnrxmhon
ROT3 xliwigvixtewwtlvewimwsjwtbugkhnxtvamgwybynjkosynipo
ROT4 ymjxjhwjyufxxumwfxjnxtkxucvhlioyuwbnhxzczoklptzojqp
ROT5 znkykixkzvgyyvnxgykoyulyvdwimjpzvxcoiyadaplmquapkrq
ROT6 aolzljylawhzzwoyhzlpzvmzwexjnkqawydpjzbebqmnrvbqlsr
ROT7 bpmamkzmbxiaaxpziamqawnaxfykolrbxzeqkacfcrnoswcrmts
ROT8 cqnbnlancyjbbyqajbnrbxobygzlpmscyafrlbdgdsoptxdsnut
ROT9 drocombodzkcczrbkcoscypczhamqntdzbgsmcehetpquyetovu
ROT10 espdpncpealddascldptdzqdaibnroueachtndfifuqrvzfupwv
ROT11 ftqeqodqfbmeebtdmequearebjcospvfbdiuoegjgvrswagvqxw
ROT12 gurfrpergcnffcuenfrvfbsfckdptqwgcejvpfhkhwstxbhwryx
ROT13 hvsgsqfshdoggdvfogswgctgdlequrxhdfkwqgilixtuycixszy
ROT14 iwthtrgtiephhewgphtxhduhemfrvsyieglxrhjmjyuvzdjytaz
ROT15 jxuiushujfqiifxhqiuyievifngswtzjfhmysiknkzvwaekzuba
ROT16 kyvjvtivkgrjjgyirjvzjfwjgohtxuakginztjlolawxbflavcb
ROT17 lzwkwujwlhskkhzjskwakgxkhpiuyvblhjoaukmpmbxycgmbwdc
ROT18 maxlxvkxmitlliaktlxblhyliqjvzwcmikpbvlnqncyzdhncxed
ROT19 nbymywlynjummjblumycmizmjrkwaxdnjlqcwmorodzaeiodyfe
ROT20 ocznzxmzokvnnkcmvnzdnjankslxbyeokmrdxnpspeabfjpezgf
ROT21 pdaoaynaplwooldnwoaeokboltmyczfplnseyoqtqfbcgkqfahg
ROT22 qebpbzobqmxppmeoxpbfplcpmunzdagqmotfzprurgcdhlrgbih
ROT23 rfcqcapcrnyqqnfpyqcgqmdqnvoaebhrnpugaqsvshdeimshcji
ROT24 sgdrdbqdsozrrogqzrdhrnerowpbfcisoqvhbrtwtiefjntidkj
ROT25 thesecretpassphraseisofspxqcgdjtprwicsuxujfgkoujelk

Vâng. Bạn có thấy cái mà tôi thấy không ạ.
Challenge này cũng khá đơn giản phải không ạ.

The Valley of Fear - 30

The hard drive may be corrupted, but you were able to recover a small chunk of text. Scribbled on the back of the hard drive is a set of mysterious numbers. Can you discover the meaning behind these numbers? (1, 9, 4) (4, 2, 8) (4, 8, 3) (7, 1, 5) (8, 10, 1)

Vâng. Một challenge về crypto. Xem nội dung file mà BTC cho nào:

It might have been expected that the attempt to trace to their origin
in the past the institutions and customs in common use upon the sea
would from an early date occupy the attention of a seafaring people,
but for some obscure reason the British nation has always been
indifferent to the history of its activities upon that element on which
its greatness was founded, and to which it has become more and more
dependent for its daily bread and its very existence. To those who
are alive to this fact it will hardly come as a surprise, therefore,
to learn that the first sustained attempt at a detailed investigation
into the history of the flag at sea was made under the patronage
of the German Admiralty by a German Admiral. Vice-Admiral Siegel's
_Die Flagge_, published in 1912, was the first book to deal with the
development of the flag at sea in a scientific spirit, and although
the earlier chapters contain some mistakes due to his employment of
translations of early works instead of original texts, and the accounts
of the British flags in the later chapters suffer because he had no
access to original records, it is a worthy piece of work.

The present book is an attempt to remove the reproach to the British
nation which this implies. Its plan is somewhat different from that
of the work referred to above. Instead of dealing with the flags of
all maritime nations of the world--a task that (if it was to be more
than a mere copying or compilation) would entail much work in foreign
archives--it seemed more profitable to concentrate upon the history
of British Naval Flags, for researches made so far back as 1908 had
taught me how much that is inaccurate about their history had received
acceptance. But first it seemed necessary to devote some time and
space to the inquiry into the origin of the flag and how it became the
honoured symbol of nationality that it now is, and for this a general
view had to be taken in order that a firm foundation might be laid for
the early history of our own flags.

In the first chapter the ground worked over by Admiral Siegel has been
solidified by examination of the original authorities, with the result
that a few errors have been detected and some new facts brought to
light, and the investigation has also been extended further; the most
important of the additions being those relating to the standards in
the Phoenician and Greek ships of war, forms of the early "standard"
and "gonfanon," and the Genoese Standard of St George and the Dragon.
For the deduction that the use of a national flag arose in the Italian
city states I take the entire responsibility, well aware that further
investigations may possibly bring to light fresh facts which will
overthrow it.

The chapter on early English, Scottish and Irish flags serves as an
introduction to the history of our national flag, which was invented
for the use of the mercantile marine, though it was very soon
appropriated by the Royal Navy for its sole use. It is very improbable
that further research will enable the gap left by the unfortunate
destruction of the early 17th century records to be filled, so that the
story of the Union Flag may be taken as being substantially complete,
but there is still room for further work upon the history of its
component crosses. It will be seen that I have been unable to find any
solid ground for the common belief that the cross of St George was
introduced as the national emblem of England by Richard I, and am of
opinion that it did not begin to attain that position until the first
years of the reign of Edward I.

The chapters on the flags used to indicate distinctions of command and
service at sea give an account of the use (now obsolete) of the Royal
Standard at sea by naval commanders-in-chief; of the history of the
Admiralty anchor-flag; and of the steps by which the present Admirals'
flags were evolved. The history of the ensigns from their first
adoption at sea about the end of Elizabeth's reign has been set out in
some detail, but further research may bring to light more details of
interest in the years between 1574 and 1653. The causes which led to
the adoption of a red ensign as the most important British ensign and
the steps which led to its appropriation to the Mercantile Marine, and
not the Royal Navy, are stated as far as the records availed, though
here again further research is needed in the late Elizabethan and
early Stuart periods among records that may still survive in private
ownership. These chapters may, perhaps, appeal rather to the seaman
and the student of naval history than to the general reader, but it is
hoped that they may also prove of service to artists who wish to avoid
the anachronisms into which some of their brethren have been betrayed.

In order that the development of flag signals may be properly
appreciated it has been necessary, when dealing with the earlier years,
to take into account what had happened outside the narrow circuit of
British waters. The earlier matter, though here examined solely from
the point of view of the flags used, offers considerable interest to
the student of naval tactics, with which indeed the art of signalling
is inseparably connected.

The last chapter, on Ceremonial and other usages, is, from the author's
point of view, the least satisfactory. From the nature of the subject,
the official records contain very little information about it. It
is only by the slow and laborious process of examining contemporary
journals, diaries, accounts of voyages, and similar material that facts
can be found for any exhaustive treatment of these matters. Something
of this has been done, but more remains to do.

In concluding the work which has occupied a large portion of the
leisure hours of many years, it is my pleasant duty to express my
gratitude to the numerous friends whose encouragement and assistance
have enabled me to persevere in what has proved a somewhat arduous
task; especially to Sir Julian Corbett, who has read the proofs and
given me the benefit of his criticisms; to the officials of the
Pepysian Library, Public Record Office, British Museum and London
Library for the facilities afforded me; and not least to my friend Mr
Vaughan who has spared no pains in the preparation of the coloured
plates.

Khá là dài và đáng sơ. Nhưng hãy chú ý vào đề bài. Các cặp 3 số (1, 9, 4) (4, 2, 8) (4, 8, 3) (7, 1, 5) (8, 10, 1) để làm gì nhỉ?? Có lẽ nào nó lần lượt chỉ (vị_trí_đoạn vị_trí_dòng vị_trí_từ) không nhỉ. Thử xem nào:
Với cặp (1, 9, 4): Đoạn thứ 1, dòng thứ 9, từ thứ 4 => the
tiếp tục (4, 2, 8): Đoạn thứ 4, dòng thứ 2, từ thứ 8 => flag
Oh! Vậy là suy luận của ta có cơ sở đây chứ " the flag" rồi cơ mà. Công việc tiếp theo đó là tìm ra các từ tiếp theo dựa trên các cặp 3 số còn lại.

Và kết quả của ta đó là:

 The flag is ceremonial plates