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cryptotask #2 - Cryptographic tasks [entries|archive|friends|userinfo]
Cryptographic tasks

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cryptotask #2 [Oct. 1st, 2005|02:10 am]
Cryptographic tasks


Предлагаю еще одну задачку. Уровень сложности, где-то 5/10.
Почувствуйте себя криптоаналитиком :)
(кому нужен русский перевод - сообщите)


Here is some story:
There are three virtual heroes: Alice, Bob and Charley
who wants to know all interesting (especially confidential)
information regarding Alice and Bob.

You are a cryptoanalyst who helps Charley. He asked you
to decrypt the last chat of Alice and Bob. You don't know
the algorithm of crypto but Charley provided you with their
some previous chat session with both pairs of plain text / cipher text,
and moreover with the key used in the crypto algorithm!

Here is previous log:

//Secure session: Setting key to 2C5B64F0AE9738D1
//Secure session: Established
Bob: Hi!
Bob^: D5B512
Alice: Halo Bob!
Alice^: D5053697B45ACA7B78
Bob: do you have SP2 installed ?
Bob^: 547592DEA870D64B7CD4CE2B8E4FEA6FA4A5ED8E38697A9BDC0906
Alice: yes i have, but i don't recommend it :)

Bob: I am deciding now... k, I won't install it

Alice: :)
Alice^: 8CB1
Bob: :) thank for tip
Bob^: 8CB1928E1849FAABF8DD0EB63C28826A
Alice: np
Alice^: 948C
//Secure session: Closed

( Legend:
( // - just comments
( ^ - crypted message
( without ^ - plain text

But now Charley has only Bob's plain text messages (maybe keylogged?)
and wants to know Alice's! So, the main goal of this crypto task
is to decrypt Alice's messages in the next chat log
after they have established a secure tunnel.
The key is unknown too. You have to reveal it.

Here is the last log:

Alice: Hi Bob!
Bob: ohh Alice! Halo!
Alice: how are you doing Bob?
Bob: I am fine! and you?
Alice: everything is cool! I have some news;)
Bob: ohh, what news? :)
Alice: is this connection secure? did you establish a secure session?
Bob: ahh, no... just a second, I'll create it
//Secure session: Setting key to: *censored*
//Secure session: Established


Alice^: 7BB6
Bob: cool!!!
Bob^: B8394A3B899AAB
Alice^: BE0F702B59E00B
Bob: :)
Bob^: 7BB6

Bob: c u
Bob^: B82610
//Secure session: Closed

What interesting news has Alice said to Bob?


Не забывайте, что решения постить нельзя, только сам факт того, что вы решили задачу :)